EquipmentPacket:AutoclaveUMDNS#:13746DateofCreation:September16,2015Creator:EngineeringWorldHealthEWHEquipmentPacketContents:Thispacketcontainsinformationabouttheoperation,maintenance,andrepairofautoclaves.PartI:ExternalfromthePacket:1. IntroductiontoAutoclaves(PowerPoint)PartII:IncludedinthisPacket:1. OperationandUse:a. BriefIntroductiontoAutoclaves(p.3)b. IntroductiontoSterilization(p.4-15)c. OperationandUseofAutoclaves(p.16-19)2. DiagramsandSchematics:a. Figure1:PhysicalMeansofMicrobialControl(p.21)3. PreventativeMaintenanceandSafety:a. DescalingtoRemoveMineralBuildup(p.23-26)b. AutoclavePreventativeMaintenance(p.27)c. AutoclavePreventativeMaintenanceTable(p.28)d. QualityControlforAutoclaves(p.29-34)4. TroubleshootingandRepair:a. AutoclaveTroubleshootingFlowchart(p.36-40)b. AutoclaveTroubleshootingTable(p.41)5. ResourcesforMoreInformation:a. ResourcesforMoreInformation(p.43)b. Bibliography(p.44-45)

*1.*Introduction*to*Autoclaves*****Featured*in*this*Section:***** Malkin,*Robert.*Medical*Instrumentation*in*the*Developing*World.*Engineering*World*Health,*2006.***Strengthening*Specialised*Clinical*Services*in*the*Pacific.*User*Care*of*Medical*Equipment:*A*first*line*maintenance*guide*for*end*users.*(2015).***Wikipedia.*“Sterilization*(Microbiology).”*Wikipedia,*p.*1d12.*Retrieved*from:***

User Care of Medical Equipment – First line maintenance for end users


Chapter 4.2 Autoclaves and Sterilizers

Sterilization is the killing of microorganisms that could harm patients. It can be done by heat (steam,

air, flame or boiling) or by chemical means. Autoclaves use high pressure steam and sterilizers use boiling water
mixed with chemicals to achieve this. Materials are placed inside the unit for a carefully specified length of
time. Autoclaves achieve better sterilization than boiling water sterilizers. Autoclaves can be small table top
designs (e.g. dental departments), portable upright units (e.g. small clinics) or large fixed systems.

How it works
Heat is delivered to water either by electricity or flame. This generates high temperature within the

chamber. The autoclave also contains high pressure when in use, hence the need for pressure control valves and
safety valves. Users must be careful to check how long items need to be kept at the temperature reached.

Sterilization (microbiology) 1

Sterilization (microbiology)
Sterilization (or sterilisation, see spelling differences) refers to any process that effectively kills or eliminates
transmissible agents (such as fungi, bacteria, viruses, spore forms, etc.) from a surface, equipment, article of food or

medication, or biological culture medium.[1] [2] Sterilization does not, however, remove prions. Sterilization can be

achieved through application of heat, chemicals, irradiation, high pressure or filtration.


The first application of sterilization by Nicolas Appert was thorough cooking to affect the partial heat sterilization of

foods and water. Cultures that practice heat sterilization of food and water have longer life expectancy and lower

rates of disability. Canning of foods by heat sterilization was an extension of the same principle. Ingestion of

contaminated food and water remains a leading cause of illness and death in the developing world, particularly for


Medicine and surgery
In general, surgical instruments and medications that enter an already sterile part of the body (such as the blood, or

beneath the skin) must have a high sterility assurance level. Examples of such instruments include scalpels,

hypodermic needles and artificial pacemakers. This is also essential in the manufacture of parenteral


Heat sterilization of medical instruments is known to have been used in Ancient Rome, but it mostly disappeared

throughout the Middle Ages resulting in significant increases in disability and death following surgical procedures.

Preparation of injectable medications and intravenous solutions for fluid replacement therapy requires not only a

high sterility assurance level, but well-designed containers to prevent entry of adventitious agents after initial


Compare sterilisation to sanitization which reduces the number of viable organisms to an acceptable level. An

example of the latter is Pasteurization.

Heat sterilization

Steam sterilization utensils

Front-loading autoclaves

A widely-used method for heat

sterilization is the autoclave,

sometimes called a converter.

Autoclaves commonly use steam

heated to 121–134 °C (250–273 °F).
To achieve sterility, a holding time of

at least 15 minutes at 121 °C (250 °F)

or 3 minutes at 134 °C (273 °F) is

required. Additional sterilizing time is

usually required for liquids and

instruments packed in layers of cloth, as they may take longer to reach the required temperature (unnecessary in


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Sterilization (microbiology) 2

machines that grind the contents prior to sterilization). Following sterilization, liquids in a pressurized autoclave
must be cooled slowly to avoid boiling over when the pressure is released. Modern converters operate around this
problem by gradually depressing the sterilization chamber and allowing liquids to evaporate under a negative
pressure, while cooling the contents.

Proper autoclave treatment will inactivate all fungi, bacteria, viruses and also bacterial spores, which can be quite
resistant. It will not necessarily eliminate all prions.

For prion elimination, various recommendations state 121–132 °C (250–270 °F) for 60 minutes or 134 °C (273 °F)
for at least 18 minutes. The prion that causes the disease scrapie (strain 263K) is inactivated relatively quickly by
such sterilization procedures; however, other strains of scrapie, as well as strains of CJD and BSE are more resistant.
Using mice as test animals, one experiment showed that heating BSE positive brain tissue at 134–138 °C
(273–280 °F) for 18 minutes resulted in only a 2.5 log decrease in prion infectivity. (The initial BSE concentration in
the tissue was relatively low). For a significant margin of safety, cleaning should reduce infectivity by 4 logs, and the
sterilization method should reduce it a further 5 logs.

To ensure the autoclaving process was able to cause sterilization, most autoclaves have meters and charts that record
or display pertinent information such as temperature and pressure as a function of time. Indicator tape is often placed
on packages of products prior to autoclaving. A chemical in the tape will change color when the appropriate
conditions have been met. Some types of packaging have built-in indicators on them.

Biological indicators ("bioindicators") can also be used to independently confirm autoclave performance. Simple
bioindicator devices are commercially available based on microbial spores. Most contain spores of the heat resistant
microbe Geobacillus stearothermophilus (formerly Bacillus stearothermophilus), among the toughest organisms for
an autoclave to destroy. Typically these devices have a self-contained liquid growth medium and a growth indicator.
After autoclaving an internal glass ampule is shattered, releasing the spores into the growth medium. The vial is then
incubated (typically at 56 °C (133 °F)) for 24 hours. If the autoclave destroyed the spores, the medium will remain
its original color. If autoclaving was unsuccessful the B. sterothermophilus will metabolize during incubation,
causing a color change during the incubation.

For effective sterilization, steam needs to penetrate the autoclave load uniformly, so an autoclave must not be
overcrowded, and the lids of bottles and containers must be left ajar. Alternatively steam penetration can be achieved
by shredding the waste in some Autoclave models that also render the end product
unrecognizable( During the initial heating of the chamber, residual air must be removed.
Indicators should be placed in the most difficult places for the steam to reach to ensure that steam actually penetrates

For autoclaving, as for all disinfection or sterilization methods, cleaning is critical. Extraneous biological matter or
grime may shield organisms from the property intended to kill them, whether it physical or chemical. Cleaning can
also remove a large number of organisms. Proper cleaning can be achieved by physical scrubbing. This should be
done with detergent and warm water to get the best results. Cleaning instruments or utensils with organic matter,
cool water must be used because warm or hot water may cause organic debris to coagulate. Treatment with
ultrasound or pulsed air can also be used to remove debris.

Although imperfect, cooking and canning are the most common applications of heat sterilization. Boiling water kills
the vegetative stage of all common microbes. Roasting meat until it is well done typically completely sterilizes the
surface. Since the surface is also the part of food most likely to be contaminated by microbes, roasting usually
prevents food poisoning. Note that the common methods of cooking food do not sterilize food - they simply reduce
the number of disease-causing micro-organisms to a level that is not dangerous for people with normal digestive and
immune systems.


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Sterilization (microbiology) 3

Pressure cooking is analogous to autoclaving and when performed correctly renders food sterile. However, some

foods are notoriously difficult to sterilize with home canning equipment, so expert recommendations should be

followed for home processing to avoid food poisoning.

Food utensils
Dishwashers often only use hot tap water or heat the water to between 49 and 60 °C (120 and 140 °F), and thus

provide temperatures that could promote bacterial growth. That is to say, they do not effectively sterilize utensils.

Some dishwashers do actually heat water up to 74 °C (165 °F) or higher; those often are specifically described as

having sterilization modes of some sort, but this is not a substitute for autoclaving.

Note that dishwashers remove food traces from the utensils by a combination of mechanical action (the action of

water hitting the plates and cutlery) and the action of detergents and enzymes on fats and proteins. This removal of

food particles thus removes one of the factors required for bacterial growth (food), it clearly explains why items with

cracks and crevices should either be washed by hand or disposed of: if the water cannot get to the area needing

cleaning, the warm, moist, dark conditions in the dishwasher can actually promote bacterial growth.

Bathing and washing are not hot enough to sterilize bacteria without scalding the skin. Most hot tap water is between

43 and 49 °C (109 and 120 °F), though some people set theirs as high as 55 °C (131 °F). Humans begin to find water

painful at 41 to 42 °C (106 to 108 °F), which to many bacteria is just starting to get warm enough for them to grow
quickly; they will grow faster, rather than be killed at temperatures up to 55 °C (131 °F) or more.

Other methods
Other heat methods include flaming, incineration, boiling, tindalization, and using dry heat.

Flaming is done to loops and straight-wires in microbiology labs. Leaving the loop in the flame of a Bunsen burner
or alcohol lamp until it glows red ensures that any infectious agent gets inactivated. This is commonly used for small

metal or glass objects, but not for large objects (see Incineration below). However, during the initial heating

infectious material may be "sprayed" from the wire surface before it is killed, contaminating nearby surfaces and

objects. Therefore, special heaters have been developed that surround the inoculating loop with a heated cage,

ensuring that such sprayed material does not further contaminate the area. Another problem is that gas flames may

leave residues on the object, e.g. carbon, if the object is not heated enough.

A variation on flaming is to dip the object in 70% ethanol (or a higher concentration) and merely touch the object

briefly to the Bunsen burner flame, but not hold it in the gas flame. The ethanol will ignite and burn off in a few

seconds. 70% ethanol kills many, but not all, bacteria and viruses, and has the advantage that it leaves less residue

than a gas flame. This method works well for the glass "hockey stick"-shaped bacteria spreaders.

Incineration will also burn any organism to ash. It is used to sanitize medical and other biohazardous waste before it
is discarded with non-hazardous waste.

Boiling in water for fifteen minutes will kill most vegetative bacteria and inactivate viruses, but boiling is
ineffective against prions and many bacterial and fungal spores; therefore boiling is unsuitable for sterilization.

However, since boiling does kill most vegetative microbes and viruses, it is useful for reducing viable levels if no

better method is available. Boiling is a simple process, and is an option available to most people, requiring only

water, enough heat, and a container that can withstand the heat; however, boiling can be hazardous and cumbersome.

Tindalization[3] /Tyndallization[4] named after John Tyndall is a lengthy process designed to reduce the level of
activity of sporulating bacteria that are left by a simple boiling water method. The process involves boiling for a

period (typically 20 minutes) at atmospheric pressure, cooling, incubating for a day, boiling, cooling, incubating for

a day, boiling, cooling, incubating for a day, and finally boiling again. The three incubation periods are to allow


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Sterilization (microbiology) 4

heat-resistant spores surviving the previous boiling period to germinate to form the heat-sensitive vegetative
(growing) stage, which can be killed by the next boiling step. This is effective because many spores are stimulated to
grow by the heat shock. The procedure only works for media that can support bacterial growth - it will not sterilize
plain water. Tindalization/tyndallization is ineffective against prions.

Dry heat sterilisator

Dry heat can be used to sterilize items, but as the heat takes much
longer to be transferred to the organism, both the time and the
temperature must usually be increased, unless forced ventilation of the
hot air is used. The standard setting for a hot air oven is at least two
hours at 160 °C (320 °F). A rapid method heats air to 190 °C (374 °F)
for 6 minutes for unwrapped objects and 12 minutes for wrapped
objects.[5] [6] Dry heat has the advantage that it can be used on powders
and other heat-stable items that are adversely affected by steam (for
instance, it does not cause rusting of steel objects).

Prions can be inactivated by immersion in sodium hydroxide (NaOH
0.09N) for two hours plus one hour autoclaving (121 °C/250 °F). Several investigators have shown complete (>7.4
logs) inactivation with this combined treatment. However, sodium hydroxide may corrode surgical instruments,
especially at the elevated temperatures of the autoclave.

Glass bead sterilizer, once a common sterilization method employed in dental offices as well as biologic
laboratories,[7] is not approved by the U.S. Food and Drug Administration (FDA) and Centers for Disease Control
and Prevention (CDC) to be used as inter-patients sterilizer since 1997.[8] Still it is popular in European as well as
Israeli dental practice although there are no current evidence-based guidelines for using this sterilizer.[7]

Chemical sterilization


Chemicals are also used for sterilization. Although heating provides
the most reliable way to rid objects of all transmissible agents, it is not
always appropriate, because it will damage heat-sensitive materials
such as biological materials, fiber optics, electronics, and many
plastics. Low temperature gas sterilizers function by exposing the
articles to be sterilized to high concentrations (typically 5 - 10% v/v) of
very reactive gases (alkylating agents such as ethylene oxide, and
oxidizing agents such as hydrogen peroxide and ozone). Liquid
sterilants and high disinfectants typically include oxidizing agents such
as hydrogen peroxide and peracetic acid and aldehydes such as
glutaraldehyde and more recently o-phthalaldehyde. While the use of
gas and liquid chemical sterilants/high level disinfectants avoids the
problem of heat damage, users must ensure that article to be sterilized
is chemically compatible with the sterilant being used. The
manufacturer of the article can provide specific information regarding compatible sterilants. In addition, the use of
chemical sterilants poses new challenges for workplace safety. The chemicals used as sterilants are designed to
destroy a wide range of pathogens and typically the same properties that make them good sterilants makes them
harmful to humans. Employers have a duty to ensure a safe work environment (Occupational Safety and Health Act
of 1970, section 5 for United States) and work practices, engineering controls and monitoring should be employed


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Sterilization (microbiology) 5

Ethylene Oxide
Ethylene oxide (EO or EtO) gas is commonly used to sterilize objects sensitive to temperatures greater than 60 °C
such as plastics, optics and electrics. Ethylene oxide treatment is generally carried out between 30 °C and 60 °C with
relative humidity above 30% and a gas concentration between 200 and 800 mg/L for at least three hours. Ethylene
oxide penetrates well, moving through paper, cloth, and some plastic films and is highly effective. Ethylene oxide
sterilizers are used to process sensitive instruments which cannot be adequately sterilized by other methods. EtO can
kill all known viruses, bacteria and fungi, including bacterial spores and is satisfactory for most medical materials,
even with repeated use. However, it is highly flammable, and requires a longer time to sterilize than any heat
treatment. The process also requires a period of post-sterilization aeration to remove toxic residues. Ethylene oxide is
the most common sterilization method, used for over 70% of total sterilizations, and for 50% of all disposable
medical devices.

The two most important ethylene oxide sterilization methods are: (1) the gas chamber method and (2) the micro-dose
method. To benefit from economies of scale, EtO has traditionally been delivered by flooding a large chamber with a
combination of EtO and other gases used as dilutants (usually CFCs or carbon dioxide). This method has drawbacks
inherent to the use of large amounts of sterilant being released into a large space, including air contamination
produced by CFCs and/or large amounts of EtO residuals, flammability and storage issues calling for special
handling and storage, operator exposure risk and training costs

Ethylene oxide is still widely used by medical device manufacturers for larger scale sterilization (e.g. by the pallet),
but while still used, EtO is becoming less popular in hospitals. Since Eto is explosive from its lower explosive limit
of 3% all the way to 100%, EtO was traditionally supplied with an inert carrier gas such as a CFC or halogenated
hydrocarbon. The use of CFCs as the carrier gas was banned because of concerns of ozone depletion [9] and
halogenated hydrocarbons are being replaced by so-called 100% EtO systems because of the much greater cost of the
blends. In hospitals, most EtO sterilizers use single use cartridges (e.g. 3M's Steri-Vac line[10], or Steris
Corporation's Stericert sterilizers[11]) because of the convenience and ease of use compared to the former plumbed
gas cylinders of EtO blends. Another 100% method is the so-called micro-dose sterilization method, developed in
the late 1950s, using a specially designed bag to eliminate the need to flood a larger chamber with EtO. This method
is also known as gas diffusion sterilization, or bag sterilization. This method minimizes the use of gas.[12]

Another reason for the decrease in use of EtO are the well known health effects. In addition to being a primary
irritant, EtO is now classified by the IARC as a known human carcinogen.[13] The US OSHA has set the permissible
exposure limit (PEL) at 1 ppm calculated as an eight hour time weighted average (TWA) [29 CFR 1910.1047] and 5
ppm as a 15 minute TWA. The NIOSH Immediately dangerous to life and health limit for EtO is 800 ppm.[14] The
odor threshold is around 500 ppm[15] and so EtO is imperceptible until concentrations well above the OSHA PEL.
Therefore, OSHA recommends that some kind of continuous gas monitoring system be used to protect workers using
EtO for sterilization.[16] While the hazards of EtO are generally well known, it should be noted that all chemical
sterilants are designed to kill a broad spectrum of organisms, by exposing them to high concentrations of reactive
chemicals. Therefore, it is no surprise that all the common chemical gas sterilants are toxic and adequate protective
measures must be taken to protect workers using these materials.

Spore testing
Bacillus subtilis, a very resistant organism, is used as a rapid biological indicator for EO sterilizers. If sterilization
fails, incubation at 37 °C causes a fluorescent change within four hours, which is read by an auto-reader. After 96
hours, a visible color change occurs. Fluorescence is emitted if a particular (EO resistant) enzyme is present, which
means that spores are still active. The color change indicates a pH shift due to bacterial metabolism. The rapid results
mean that the objects treated can be quarantined until the test results are available.


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Sterilization (microbiology) 6

Ozone is used in industrial settings to sterilize water and air, as well as a disinfectant for surfaces. It has the benefit
of being able to oxidize most organic matter. On the other hand, it is a toxic and unstable gas that must be produced
on-site, so it is not practical to use in many settings.

Ozone offers many advantages as a sterilant gas; ozone is a very efficient sterilant because of its strong oxidizing
properties (E = 2.076 vs SHE, CRC Handbook of Chemistry and Physics, 76th Ed, 1995-1996) capable of destroying
a wide range of pathogens, including prions[17] without the need for handling hazardous chemicals since the ozone is
generated within the sterilizer from medical grade oxygen. In 2005 a Canadian company called TSO3 Inc[18]

received FDA clearance to sell an ozone sterilizer for use in healthcare. The high reactivity of ozone means that
waste ozone can be destroyed by passing over a simple catalyst that reverts it back to oxygen and also means that the
cycle time is relatively short (about 4.5 hours for TSO3's model 125L). The downside of using ozone is that the gas
is very reactive and very hazardous. The NIOSH immediately dangerous to life and health limit for ozone is 5 ppm,
much 160 times smaller than the 800 ppm IDLH for ethylene oxide.Documentation for Immediately Dangerous to
Life or Health Concentrations (IDLH): NIOSH Chemical Listing and Documentation of Revised IDLH Values (as of
3/1/95) [19] and OSHA has set the PEL for ozone at 0.1 ppm calculated as an eight hour time weighted average (29
CFR 1910.1000, Table Z-1). The Canadian Center for Occupation Health and Safety provides an excellent summary
of the health effects of exposure to ozone.[20] The sterilant gas manufacturers include many safety features in their
products but prudent practice is to provide continuous monitoring to below the OSHA PEL to provide a rapid
warning in the even of a leak and monitors for determining workplace exposure to ozone are commercially available.

Chlorine bleach is another accepted liquid sterilizing agent. Household bleach consists of 5.25% sodium
hypochlorite. It is usually diluted to 1/10 immediately before use; however to kill Mycobacterium tuberculosis it
should be diluted only 1/5, and 1/2.5 (1 part bleach and 1.5 parts water) to inactivate prions. The dilution factor must
take into account the volume of any liquid waste that it is being used to sterilize.[21] Bleach will kill many organisms
immediately, but for full sterilization it should be allowed to react for 20 minutes. Bleach will kill many, but not all
spores. It is also highly corrosive.

Bleach decomposes over time when exposed to air, so fresh solutions should be made daily.[22]

Glutaraldehyde and Formaldehyde
Glutaraldehyde and formaldehyde solutions (also used as fixatives) are accepted liquid sterilizing agents, provided
that the immersion time is sufficiently long. To kill all spores in a clear liquid can take up to 12 hours with
glutaraldehyde and even longer with formaldehyde. The presence of solid particles may lengthen the required period
or render the treatment ineffective. Sterilization of blocks of tissue can take much longer, due to the time required for
the fixative to penetrate. Glutaraldehyde and formaldehyde are volatile, and toxic by both skin contact and
inhalation. Glutaraldehyde has a short shelf life (<2 weeks), and is expensive. Formaldehyde is less expensive and
has a much longer shelf life if some methanol is added to inhibit polymerization to paraformaldehyde, but is much
more volatile. Formaldehyde is also used as a gaseous sterilizing agent; in this case, it is prepared on-site by
depolymerization of solid paraformaldehyde. Many vaccines, such as the original Salk polio vaccine, are sterilized
with formaldehyde.


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Sterilization (microbiology) 7

Ortho-phthalaldehyde (OPA) is a chemical sterilizing agent that received Food and Drug Administration (FDA)
clearance in late 1999. Typically used in a 0.55% solution, OPA shows better myco-bactericidal activity than

glutaraldehyde. It also is effective against glutaraldehyde-resistant spores. OPA has superior stability, is less volatile,

and does not irritate skin or eyes, and it acts more quickly than glutaraldehyde. On the other hand, it is more

expensive, and will stain proteins (including skin) gray in color.

Hydrogen Peroxide
Hydrogen peroxide is another chemical sterilizing agent. It is relatively non-toxic when diluted to low
concentrations, such as the familiar 3% retail solutions although hydrogen peroxide is a dangerous oxidizer at high

concentrations (> 10% w/w). Hydrogen peroxide is strong oxidant and these oxidizing properties allow it to destroy

a wide range of pathogens and it is used to sterilize heat or temperature sensitive articles such as rigid endoscopes. In

medical sterilization hydrogen peroxide is used at higher concentrations, ranging from around 35% up to 90%. The

biggest advantage of hydrogen peroxide as a sterilant is the short cycle time. Whereas the cycle time for ethylene

oxide (discussed above) may be 10 to 15 hours, the use of very high concentrations of hydrogen peroxide allows

much shorter cycle times. Some hydrogen peroxide modern sterilizers, such as the Sterrad NX have a cycle time as

short as 28 minutes.

Hydrogen peroxide sterilizers have their drawbacks. Since hydrogen peroxide is a strong oxidant, there are material

compatibility issues and users should consult the manufacturer of the article to be sterilized to ensure that it is

compatible with this method of sterilization. Paper products cannot be sterilized in the Sterrad system because of a

process called cellulostics, in which the hydrogen peroxide would be completely absorbed by the paper product. The

penetrating ability of hydrogen peroxide is not as good as ethylene oxide and so there are limitations on the length

and diameter of lumens that can be effectively sterilized and guidance is available from the sterilizer manufacturers.

While hydrogen peroxide offers significant advantages in terms of throughput, as with all sterilant gases, sterility is

achieved through the use of high concentrations of reactive gases. Hydrogen peroxide is primary irritant and the

contact of the liquid solution with skin will cause bleaching or ulceration depending on the concentration and contact

time. The vapor is also hazardous with the target organs being the eyes and respiratory system. Even short term

exposures can be hazardous and NIOSH has set the Immediately Dangerous to Life and Health Level (IDLH) at 75

ppm.[14] less than one tenth the IDLH for ethylene oxide (800 ppm). Prolonged exposure to even low ppm

concentrations can cause permanent lung damage and consequently OSHA has set the permissible exposure limit to

1.0 ppm, calculated as an 8 hour time weighted average (29 CFR 1910.1000 Table Z-1). Employers thus have a legal

duty to ensure that their personnel are not exposed to concentrations exceeding this PEL. Even though the sterilizer

manufacturers go to great lengths to make their products safe through careful design and incorporation of many

safety features, workplace exposures of hydrogen peroxide from gas sterilizers are documented in the FDA MAUDE

database.[23] When using any type of gas sterilizer, prudent work practices will include good ventilation (10 air

exchanges per hour), a continuous gas monitor for hydrogen peroxide as well as good work practices and training.

Further information about the health effects of hydrogen peroxide and good work practices is available from

OSHA[24] and the ATSDR.[25]

Hydrogen peroxide can also be mixed with formic acid as needed in the Endoclens device for sterilization of

endoscopes. This device has two independent asynchronous bays, and cleans (in warm detergent with pulsed air),

sterilizes and dries endoscopes automatically in 30 minutes. Studies with synthetic soil with bacterial spores showed

the effectiveness of this device.


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Sterilization (microbiology) 8

Dry sterilization process
Dry sterilization process (DSP) uses hydrogen peroxide at a concentration of 30-35% under low pressure
conditions. This process achieves bacterial reduction of 10-6...10-8. The complete process cycle time is just 6
seconds, and the surface temperature is increased only 10-15 °C (18 to 27 °F). Originally designed for the
sterilization of plastic bottles in the beverage industry, because of the high germ reduction and the slight temperature
increase the dry sterilization process is also useful for medical and pharmaceutical applications.

Peracetic acid
Peracetic acid (0.2%) is used to sterilize instruments in the Steris system.

Prions are highly resistant to chemical sterilization. Treatment with aldehydes (e.g., formaldehyde) have actually
been shown to increase prion resistance. Hydrogen peroxide (3%) for one hour was shown to be ineffective,
providing less than 3 logs (10−3) reduction in contamination. Iodine, formaldehyde, glutaraldehyde and peracetic
acid also fail this test (one hour treatment). Only chlorine, a phenolic compound, guanidinium thiocyanate, and
sodium hydroxide (NaOH) reduce prion levels by more than 4 logs. Chlorine and NaOH are the most consistent
agents for prions. Chlorine is too corrosive to use on certain objects. Sodium hydroxide has had many studies
showing its effectiveness.

Silver ions and silver compounds show a toxic effect on some bacteria, viruses, algae and fungi, typical for heavy
metals like lead or mercury, but without the high toxicity to humans that is normally associated with these other
metals. Its germicidal effects kill many microbial organisms in vitro, but testing and standardization of silver
products is yet difficult.[26]

Hippocrates, the father of modern medicine, wrote that silver had beneficial healing and anti-disease properties, and
the Phoenicians used to store water, wine, and vinegar in silver bottles to prevent spoiling. In the early 1900s people
would put silver dollars in milk bottles to prolong the milk's freshness.[27] The exact process of silver's germicidal
effect is still not well understood. One of the explanations is the oligodynamic effect, which accounts for the effect
on microorganisms but not on viruses.
Silver compounds were used to prevent infection in World War I before the advent of antibiotics. Silver nitrate
solution was a standard of care but was largely replaced by silver sulfadiazine cream (SSD Cream),[28] which was
generally the "standard of care" for the antibacterial and antibiotic treatment of serious burns until the late 1990s.[29]

Now, other options, such as silver-coated dressings (activated silver dressings), are used in addition to SSD cream.
However, the evidence for the use of such silver-treated dressings is mixed and although the evidence on if they are
effective is promising, it is marred by the poor quality of the trials used to assess these products.[30] Consequently a
major systematic review by the Cochrane Collaboration found insufficient evidence to recommend the use of
silver-treated dressings to treat infected wounds.[30]

The widespread use of silver went out of fashion with the development of antibiotics. However, recently there has
been renewed interest in silver as a broad-spectrum antimicrobial. In particular, silver is being used with alginate, a
naturally occurring biopolymer derived from seaweed, in a range of products designed to prevent infections as part
of wound management procedures, particularly applicable to burn victims.[31] In 2007, AGC Flat Glass Europe
introduced the first antibacterial glass to fight hospital-caught infection: it is covered with a thin layer of silver.[32] In
addition, Samsung has introduced washing machines with a final rinse containing silver ions to provide several days
of antibacterial protection in the clothes.[33] Kohler has introduced a line of toilet seats that have silver ions
embedded to kill germs. A company called Thomson Research Associates has begun treating products with Ultra
Fresh, an anti-microbial technology involving "proprietary nano-technology to produce the ultra-fine silver particles


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Sterilization (microbiology) 9

essential to ease of application and long-term protection."[34] The U.S. Food and Drug Administration (FDA) has
recently approved an endotracheal breathing tube with a fine coat of silver for use in mechanical ventilation, after
studies found it reduced the risk of ventilator-associated pneumonia.[35]

It has long been known that antibacterial action of silver is enhanced by the presence of an electric field. Applying a
few volts of electricity across silver electrodes drastically enhances the rate that bacteria in solution are killed. It was
found recently that the antibacterial action of silver electrodes is greatly improved if the electrodes are covered with
silver nanorods.[36] Note that enhanced antibacterial properties of nanoparticles compared to bulk material is not
limited to silver, but has also been demonstrated on other materials such as ZnO[37]

Radiation Sterilization
Methods of sterilization exist using radiation such as electron beams, X-rays, gamma rays, or subatomic particles.[38]

• Gamma rays are very penetrating and are commonly used for sterilization of disposable medical equipment, such
as syringes, needles, cannulas and IV sets. Gamma radiation requires bulky shielding for the safety of the
operators; they also require storage of a radioisotope (usually Cobalt-60), which continuously emits gamma rays
(it cannot be turned off, and therefore always presents a hazard in the area of the facility).

• Electron beam processing is also commonly used for medical device sterilization. Electron beams use an on-off
technology and provide a much higher dosing rate than gamma or x-rays. Due to the higher dose rate, less
exposure time is needed and thereby any potential degradation to polymers is reduced. A limitation is that
electron beams are less penetrating than either gamma or x-rays.

• X-rays, High-energy X-rays (bremsstrahlung) are a form of ionizing energy allowing to irradiate large packages
and pallet loads of medical devices. Their penetration is sufficient to treat multiple pallet loads of low-density
packages with very good dose uniformity ratios. X-ray sterilization is an electricity based process not requiring
chemical nor radio-active material. High energy and high power X-rays are generated by an X-ray machine that
can be turned off for servicing and when not in use.

• Ultraviolet light irradiation (UV, from a germicidal lamp) is useful only for sterilization of surfaces and some
transparent objects. Many objects that are transparent to visible light absorb UV. UV irradiation is routinely used
to sterilize the interiors of biological safety cabinets between uses, but is ineffective in shaded areas, including
areas under dirt (which may become polymerized after prolonged irradiation, so that it is very difficult to
remove). It also damages many plastics, such as polystyrene foam.

• Subatomic particles may be more or less penetrating, and may be generated by a radioisotope or a device,
depending upon the type of particle.

Irradiation with X-rays or gamma rays does not make materials radioactive. Irradiation with particles may make
materials radioactive, depending upon the type of particles and their energy, and the type of target material: neutrons
and very high-energy particles can make materials radioactive, but have good penetration, whereas lower energy
particles (other than neutrons) cannot make materials radioactive, but have poorer penetration.

Irradiation is used by the United States Postal Service to sterilize mail in the Washington, DC area. Some foods (e.g.
spices, ground meats) are irradiated for sterilization (see food irradiation).

Sterile filtration
Clear liquids that would be damaged by heat, irradiation or chemical sterilization can be sterilized by mechanical
filtration. This method is commonly used for sensitive pharmaceuticals and protein solutions in biological research.
A filter with pore size 0.2 µm will effectively remove bacteria. If viruses must also be removed, a much smaller pore
size around 20 nm is needed. Solutions filter slowly through membranes with smaller pore diameters. Prions are not
removed by filtration. The filtration equipment and the filters themselves may be purchased as pre-sterilized
disposable units in sealed packaging, or must be sterilized by the user, generally by autoclaving at a temperature that


Wikipedia. “Sterilization (Microbiology).” Wikipedia, p. 1-12. Retrieved from:


Sterilization (microbiology) 10

does not damage the fragile filter membranes. To ensure sterility, the filtration system must be tested to ensure that
the membranes have not been punctured prior to or during use.

To ensure the best results, pharmaceutical sterile filtration is performed in a room with highly filtered air (HEPA
filtration) or in a laminar flow cabinet or "flowbox", a device which produces a laminar stream of HEPA filtered air.

See also
• Asepsis
• Antibacterial soap
• Contamination control
• Electron irradiation
• Pasteurization


General references
• Ninemeier J. Central Service Technical Manual [39] (6th ed.). International Association of Healthcare Central

Service Materiel Management.
• Control of microbes [40]

• Raju GK, Cooney CL (1993). "Media and air sterilization". in Stephanopoulos G. Biotechnology, 2E, Vol. 3,
Bioprocessing. Weinheim: Wiley-VCH. pp. 157–84. ISBN 3-527-28313-7.

External links
• Chemical Disinfection [41]

• Sterilizer Cleaning and Maintenance [42]

• Materials Management Microsystems, the leader in sterile processing management software [43]


[1] WHO Glossary (http:/ / www. who. int/ reproductive-health/ publications/ MSM_98_4/ MSM_98_4_glossary. en. html)
[2] UCLA Dept. Epidemiology: Definitions (http:/ / www. ph. ucla. edu/ epi/ bioter/ anthapha_def_a. html)
[3] Mesquita, J. A. M.; Teixeira, M.A. and Brandao, S. C. C. (1998). "Tindalization of goats' milk in glass bottles" (http:/ / www. asas. org/ jas/

98meet/ 98df. pdf). J. Anim. Sci. /J. Dairy Sci. Vol. 76, Suppl. 1 / Vol. 81, Suppl. 1/: 21. . Retrieved 2007-03-06.
[4] Thiel, Theresa (1999). "" (http:/ / www. umsl. edu/ ~microbes/ pdf/ tyndallization. pdf) (pdf). Science in the Real World. . Retrieved

[5] (http:/ / www. health. gov. ab. ca/ resources/ publications/ PersonalServicesPt1. pdf)
[6] Dental Volume 1 - Dentist training manual for military dentists (http:/ / www. tpub. com/ content/ medical/ 14274/ css/ 14274_146. htm)
[7] Zadik Y, Peretz A (Apr 2008). "The effectiveness of glass bead sterilizer in the dental practice". J Isr Dent Assoc 25 (2): 36–9.

PMID 18780544.
[8] http:/ / www. CDC. gov/ OralHealth/ InfectionControl/ faq/ bead. htm 2008-09-11
[9] http:/ / www. epa. gov/ Ozone/ snap/ sterilants/ sterilants. pdf
[10] http:/ / solutions. 3m. com/ wps/ portal/ 3M/ en_US/ MedicalSpecialties/ devices/ products/ medical-sterilization/ equipment/
[11] http:/ / www. stericert. com/ eo/ index. html
[12] Micro-dose sterilization method (http:/ / anpro. com/ articles/ eto benefits. htm)
[13] http:/ / monographs. iarc. fr/ ENG/ Monographs/ vol60/ volume60. pdf
[14] http:/ / www. cdc. gov/ niosh/ idlh/ intridl4. html
[15] http:/ / www. atsdr. cdc. gov/ MHMI/ mmg137. html
[16] http:/ / www. osha. gov/ SLTC/ etools/ hospital/ central/ central. html
[17] http:/ / www. tso3. com/ en/ news-events/ news-tso3-gets-promising-223. php
[18] http:/ / www. tso3. com


Wikipedia. “Sterilization (Microbiology).” Wikipedia, p. 1-12. Retrieved from:


Sterilization (microbiology) 11

[19] http:/ / www. cdc. gov/ niosh/ idlh/ intridl4. html
[20] http:/ / www. ccohs. ca/ oshanswers/ chemicals/ chem_profiles/ ozone/ basic_ozo. html
[21] Beth Israel Deaconess Medical Center Biosafety Manual (2004 edition)
[22] Office of Health and Safety (2007). Biosafety in Microbiological and Biomedical Laboratories (BMBL) (http:/ / www. cdc. gov/ OD/ ohs/

biosfty/ bmbl5/ bmbl5toc. htm) (5th ed.). Centers for Disease Control and Prevention. .
[23] http:/ / www. accessdata. fda. gov/ scripts/ cdrh/ cfdocs/ cfMAUDE/ search. CFM
[24] http:/ / www. osha. gov/ SLTC/ healthguidelines/ hydrogenperoxide/ recognition. html
[25] http:/ / www. atsdr. cdc. gov/ MHMI/ mmg174. html
[26] Chopra I (April 2007). "The increasing use of silver-based products as antimicrobial agents: a useful development or a cause for concern?".

The Journal of antimicrobial chemotherapy 59 (4): 587–90. doi:10.1093/jac/dkm006. PMID 17307768.
[27] "Antibacterial effects of silver" (http:/ / www. saltlakemetals. com/ Silver_Antibacterial. htm). .
[28] Chang TW, Weinstein L (December 1975). "Prevention of herpes keratoconjunctivitis in rabbits by silver sulfadiazine" (http:/ / aac. asm.

org/ cgi/ pmidlookup?view=long& pmid=1211919). Antimicrob. Agents Chemother. 8 (6): 677–8. PMID 1211919. PMC 429446. .
[29] Atiyeh BS, Costagliola M, Hayek SN, Dibo SA (March 2007). "Effect of silver on burn wound infection control and healing: review of the

literature". Burns : journal of the International Society for Burn Injuries 33 (2): 139–48. doi:10.1016/j.burns.2006.06.010. PMID 17137719.
[30] Lo SF, Hayter M, Chang CJ, Hu WY, Lee LL (August 2008). "A systematic review of silver-releasing dressings in the management of

infected chronic wounds". Journal of clinical nursing 17 (15): 1973–85. doi:10.1111/j.1365-2702.2007.02264.x. PMID 18705778.
[31] Hermans MH (December 2006). "Silver-containing dressings and the need for evidence". The American journal of nursing 106 (12): 60–8;

quiz 68–9. PMID 17133010.
[32] "AGC Flat Glass Europe launches world’s first antibacterial glass" (http:/ / www. agc-flatglass. eu/ AGC+ Flat+ Glass+ Europe/ English/

Homepage/ News/ Press+ room/ Press-Detail-Page/ page. aspx/ 979?pressitemid=1031). 2007-09-04. .
[33] "Samsung laundry featuring SilverCare Technology" (http:/ / web. archive. org/ web/ 20060531115914/ http:/ / www. samsung. com/

PressCenter/ PressRelease/ PressRelease. asp?seq=20060213_0000233684). Samsung. . Retrieved 2007-08-06.
[34] ""Ultra-Fresh technology is based on the power of silver to fight bacteria"" (http:/ / www. expresstextile. com/ 20050731/ perspectives01.

shtml). Express Textile. .
[35] "FDA Clears Silver-Coated Breathing Tube For Marketing" (http:/ / www. fda. gov/ bbs/ topics/ NEWS/ 2007/ NEW01741. html).

2007-11-08. . Retrieved 2007-11-11.
[36] O. Akhavan and E. Ghaderi "Enhancement of antibacterial properties of Ag nanorods by electric field" Sci. Technol. Adv. Mater. 10 (2009)

015003 free download (http:/ / www. iop. org/ EJ/ abstract/ 1468-6996/ 10/ 1/ 015003)
[37] N. Padmavathy et al. "Enhanced bioactivity of ZnO nanoparticles—an antimicrobial study" Sci. Technol. Adv. Mater. 9 (2007) 035004 free

download (http:/ / dx. doi. org/ 10. 1088/ 1468-6996/ 9/ 3/ 035004)
[38] Trends in Radiation Sterilization of Health Care Products (http:/ / www-naweb. iaea. org/ napc/ iachem/ publications. html), IAEA,

Vienna,24 September 2008
[39] http:/ / cbspd. net/ cstechpub. htm
[40] http:/ / www. bact. wisc. edu/ Microtextbook/ modules. php?op=modload& name=Sections& file=index& req=viewarticle& artid=13&

[41] http:/ / www. instrumentcleaning. com/ chemical_disinfection. html
[42] http:/ / www. mohawkmedicalmall. com/ manufacturer-related/ tuttnauer-sterilizer-autoclave-cleaning. php
[43] http:/ / www. mmmicrosystems. com/


Wikipedia. “Sterilization (Microbiology).” Wikipedia, p. 1-12. Retrieved from:


Article Sources and Contributors 12

Article Sources and Contributors
Sterilization (microbiology)  Source:  Contributors: 1guzik1, AGToth, Aboalbiss, Alansohn,, Anaxial, Arrataz,
Bender235, Berbania, Beteigeuze, Big Bob the Finder, Bobo192, Bodenlarson, Bongwarrior, Brian0918, COMPFUNK2, CanisRufus, Capricorn42, Captain panda, CaseInPoint, Chatzi,
Christopherlin, Clairestreb, ClamsonJ, Cp.7777, Crystallina, DA3N, Darth Panda, DataMatrix, Dethierp, Drsib, E0steven, ESkog, Emperorbma, Epolk, Evahala, Everyking, Excirial, Fadesga,
Femto, Fusionmix, Gaius Cornelius, Gene Nygaard, Gioto, Glane23, Glen, HGYAIT, Hairy Dude, Halien0101, Harvestman, HexaChord, Infofarmer, J.delanoy, Jcasarini, Jeff G.,
Jeffrey.Rodriguez, JeffreyN, Jibbajabba, Jpbarbier, Jqcalhoun, Jsmith86, Juan de Vojníkov, Juliancolton, Jutta, Jyril, Kazvorpal, Kelly Martin, Killfoot, Krystianh, Light current, Luckylouis, Luna
Santin, M1ss1ontomars2k4, MBisanz, MKFM, Mark Foskey, Materialscientist, Medic, Melchoir, Mglg, Miaow Miaow, Microbiojen, Mnd, Mraynerb, Mysid, Neelix, Nehrams2020, Ninly,
One-dimensional Tangent, Oneirist, P.B. Pilhet, Piano non troppo, Pixie, Playtime, Quincy8Boy, R. Engelhardt, RDBrown, Rafti Institute, Renato Caniatti, Reo On, Rholton, Rich Farmbrough,
Rsteif, Rwarburton, SQGibbon, Salvadorjo, Sam907, Sangriademuertos, Sarindam7, Scaraway, Scharks, Serephine, Shbrown, SirGrant, Snigbrook, SpeedyGonsales, Spellman999, Steveprutz,
Suffusion of Yellow, Swpb, Teflex77, TenOfAllTrades, Thatotter, TimVickers, Tins128, Tobias Bergemann, Tom David, Tomas e, Topbanana, Tristanb, Triwbe, Tyler Berry, Udaza, Varikse,
Veganguy, Vigorous action, Vitaleyes, WAS 4.250, Wedian, West London Dweller, Wordsweek11, WriterHound, Xbgs351, Xephael, ZacBowling, Zeamays, Zhang He, , 194 anonymous edits

Image Sources, Licenses and Contributors
Image:Autoclave Front Loading composition.jpg  Source:  License: Attribution  Contributors:
File:2003-12-03-Heissluft-Sterilisator.JPG  Source:  License: Creative Commons Attribution-Sharealike
3.0  Contributors: R. Engelhardt
File:2003-12-03-Chemiclav.JPG  Source:  License: Creative Commons Attribution-Sharealike 3.0  Contributors: R.

Creative Commons Attribution-Share Alike 3.0 Unported
http:/ / creativecommons. org/ licenses/ by-sa/ 3. 0/


Frank’s Hospital Workshop. “Sterilization (Microbiology).” Frank’s Hospital Workshop, p. 1-12.

Retrieved from:


Wikipedia. “Sterilization (Microbiology).” Wikipedia, p. 1-12. Retrieved from:


Equipment Found in the Clinical Laboratory

3.7 Autoclaves

3.7.1 Use and Principles of Operation
An autoclave is a device used to sterilize medical instruments and equipment. It uses steam and
pressure in the absence of air to assure sterile conditions. The small, table-top autoclave uses
heat to boil water into steam. The steam continues heating and the pressure continues to
increase. Bacteria cannot survive in these conditions. However, not all viruses and spores are
killed. Exposing materials to a single heat cycle is somewhat effective, but sterilizing them 3
times over a period of 3 days will kill most vegetative spores.

Inside and outside of a small, electric autoclave.

Most hospitals have electric, steam autoclaves, but you will also find an autoclave like the “All
American” distributed by UNICEF. It uses an open fire as its source of heat.

The small open fire autoclave is still common in the developing world.

An autoclave is a fairly simple instrument to operate but could be dangerous if operated
improperly. It is important to wait until the chamber is completely depressurized before opening!
If it is opened under pressure, large quantities of steam could escape causing severe burns!
Most modern hospitals have automated autoclaves. These devices go through the steps of
operation without intervention. If the machine is not going through its steps correctly, there is
little that can be done to change the sequence of steps.

Manual machines, such as the All American, must be operated correctly to insure sterilization.
The automated machines follow the same steps, though automatically.

Start by making sure that the water reservoir is filled to proper level with distilled water or
filtered rain water. Well water will, in time, leave a scaly deposit on the instruments and
autoclave. An indicator strip should be used with each pack being sterilized. However, in the
developing world, this practice is not followed. Place the instruments into the chamber and close
lid securely. Open the air outlet valve. Automated machines may use several cycles of vacuum
to remove the air. The manual machines depend on the steam to push the air out of the

Now, the machine is ready to begin its cycle. Turn on or light the heating element. During this
part of the cycle, the manual machine is evacuating the air. Therefore, it is important to wait
until there is a steady stream of steam exiting from the autoclave. If the air release valve is


Principles of Use and Operation: From Medical Instrumentation in the Developing World

Malkin, Robert. Medical Instrumentation in the Developing World. Engineering World Health, 2006.

Medical Instruments in the Developing World Malkin

spitting and sputtering, it should remain open. Air left in the chamber will lead to cold spots, and
poor sterilization.

When the air is completely evacuated from the machine, either by vacuum in the automated
machines or by steam in the manual machines, the air outlet valve must be closed. The steam
pressure will begin to rise. At this point, it is sufficient to monitor the temperature and time to
insure sterilization. Do not open the chamber or valves, as the pressure of the escaping steam
can be dangerous.

The sterilization cycle and sometimes the cool-down cycle can be timed. The proper time and
temperature is shown below for unwrapped surgical instruments. Allow 30 minutes more at the
holding temperature and pressure if the instruments are wrapped.
Temperature ( C )

pressure (kPa)

pressure (psi)

Minimum holding
time (min)

Overall time

115 75 11 30 50
122 115 17 15 40
128 150 22 10 30
136 225 33 3 20

After the specified holding time, the sterilization cycle is complete. Turn the heating element off
completely. Now the cool-down cycle begins. The progress of cool-down can be followed by
time, temperature, or simply by dropping water on the outside of the vessel. If it boils off, the
vessel is still too hot. When cool down is complete, the chamber can be opened. If a
sterilization tape was used, check to see that it is completely black.

3.7.2 Common Problems
There are a number of different types of problems you may encounter. However, the manual
autoclave is a very reliable instrument. It rarely fails when properly operated and maintained.

The most common problem in the developing world is a buildup of a scale due to the use of
non-distilled water in the sterilization cycle. The scale can usually be scraped off the machine
and simply thrown away. On manual machines, the scale may cause the air release valve and
the over-pressure relief valve to be clogged. Both of these systems are difficult to scrape clean.
If they can be removed from the machine and forced or left open, then simply soaking them for
several days in pure distilled water should dissolve any deposits. It may be best to run a few
dozen cycles with distilled water, where the air release valve is intentionally left open (steam will
escape through the valve the entire cycle). This will help to dissolve any remaining the scale. If
the relief valve cannot be opened and cleaned, it is best to replace this component.

Automated machines with scale build up may also see clogs in the vacuum lines and associated
valves. If the machine is still operable, the best procedure may be to remove any visible build
up, then run many cycles with pure distilled water until the remaining scale dissolves. If the
valves have become blocked, remove them all and clean them all (not just the clogged one). If
only one is clogged, it is certain that the others are close.

The second most common problem for autoclaves in the developing world is clogging of filters
due to the use of dirty water, such as non-filtered rain water. This primarily plagues the
automated autoclaves which often have inlet filters between the water storage and the main
vessel. Some of these filters can be removed and back-flushed (run water backwards through
the filter) to clean and restore them. Be sure to clean the tank of any particles that have settled
to the bottom. In other cases, the filter must be replaced.


Malkin, Robert. Medical Instrumentation in the Developing World. Engineering World Health, 2006.

Equipment Found in the Clinical Laboratory

If you hear a hissing noise, then there is a leak in the pressure vessel or valve. Try to isolate the
problem by looking for steam escaping and by using your ear. If the problem is a valve, it will
probably be necessary to replace the valve. If the problem is the vessel, it is impossible to fix
and the autoclave should be discarded. The seal on the vessel is also a common source of leaks.
Check to see that there are no obstructions (dirt, or scale build up) along the seal. In some
cases, the seal can be reground, but often, replacing the seal is required.

Some machines use a plastic or rubber seal. For these machines, run your fingernail into the
seal. It should be pliable. If the seal is hard, or worse cracked, then it must be replaced. In
larger cities, you may be able to find an automobile repair shop that can cut you a replacement
gasket. Silicone sealant can be used to seal cracks in door gaskets until a replacement gasket
can be located and installed.

If the seals are working and there are no leaks or clogs, the manual autoclave should work. The
automatic autoclave may still not reach the proper temperature. The cause may be the
thermostat or the heating element. In the most sophisticated autoclaves, the controller can be

If there is no heat generated, it could be the heating element or the thermostats. The typical
heating element consists of two coils of nickel-chrome resistance wire, each of which has
approximately 14 ohms of resistance. If the resistance across a coil is significantly higher, it is
probably broken. These heaters are paralleled and the combination is placed in series with the
on/off switch and one or both of the thermostats. Nicrome wire is common and can usually be
found in the developing world. Match the resistance and length as closely as possible.

Circuit of a simple, electric autoclave.

There are often two thermostats. One is a boil-dry safety thermostat connected in series with
one of the elements and set to open at 212 degrees F. This will reduce the violence of boiling
once 212 is reached. The second thermostat, often called the overheat relay, is set to turn off
the electricity going to the nicrome elements when the temperature is excessive, usually
meaning that the water has boiled away. Both thermostats for this instrument are usually of
the bimetallic-switch type. They rarely degrade themselves, but the device which holds them in
place often deteriorates.

3.7.3 Suggested Testing
Autoclaves are like centrifuges in that there is a safety issue associated with their use. The
device can injure the operator or leave the equipment undetectably contaminated. Therefore,
some testing should be performed before releasing the device for use.

Before releasing an autoclave back to the floor, check the gaskets and check for scaling. You can
prevent future clogging by removing any scale or dirt now. If the gasket for the vessel breaks, it


Malkin, Robert. Medical Instrumentation in the Developing World. Engineering World Health, 2006.

Medical Instruments in the Developing World Malkin

may leak steam, which can be dangerous. If the autoclave has an interlock that prevents
opening during a cycle, check this again for safety.

If possible, check the temperature inside the vessel during sterilization. Most US hospital users put
test strips with each sterilization pack. These strips verify that the temperature reached the required
level for the required time and that humidity was present. However, in the developing world, these
test strips are rarely used. It is nevertheless, possible to test the autoclave.

A complete test of an autoclave includes a Bowie-Dick test (to see that all the air was being removed)
and either a temperature or a pressure test to see if the temperature and pressure reached the
needed levels (since PV=nRT, and the chamber is only filled with steam, it is not necessary to
measure both temperature and pressure). The time of the sterilization cycle can be measured with a
watch. The Bowie-Dick test for air removal can be approximated by placing a standard Time-
Temperature test strip on a sheet of paper in the center of a stack of 100% cotton towels and placed
in a metal dressing can. The dressing can is placed in a warmed pre vac sterilizer and a short cycle is
run using the tape on the cotton towels as a check. If there is any air left in the sterilizer chamber,
then it would be trapped in the towels. Because the air would not allow the steam to touch the tape,
the color change would not be uniform around the strip. In order to pass the test, the entire tape
must change colors, not just the edges. This procedure will test both the temperature and the air
removal process.

If test strips are not available, then it is not possible to reliably test the autoclave for both air removal
and temperature/pressure. You will have to settle for a pressure measurement. At the present time,
there is no reusable alternative to the test strips readily available in the developing world.

Check the safety valve on the vessel. If it is dirty or corroded, attempt to replace it. If you cannot
replace it, it is possible to test the safety valve by bypassing the overheat limit switch. This should
only be attempted by experienced technicians wearing proper safety gear. Furthermore, you can
only test the safety valve on autoclaves with working pressure gages. The safety valve is factory
set to open at 30 psi. To test this valve, short out the thermostat with a clip lead, operate the
autoclave as in starting a normal cycle. Be ready to pull the plug from the wall very quickly,
should the safety valve fail and the pressure rise above 31 psi. If the safety valve fails to operate
at this upper limit, it must be replaced. If you cannot find a replacement, discuss the danger with
the administration. Although not having a safety valve is a severe danger to the operator, not
having an autoclave is a severe danger to the patients.


2.*Autoclave*Schematics*and*Diagrams** ****Featured*in*this*Section:*****Discover*Biotech.*“Physical*Means*of*Microbial*Control.”*Retrieved*from:**

Figure 1: Physical Means of Microbial Control


3.*Preventative*Maintenance******Featured*in*this*Section:****Cooper,*Justin*and*Alex*Dahinten*for*EWH.*“Autoclave*Preventative*Maintenance.”*From*the*publication:*Medical*Equipment*Troubleshooting*Flowchart*Handbook.*Durham,*NC:*Engineering*World*Health,*2013.** *EWH.*“Descaling*to*Remove*Mineral*Buildup.”*Engineering*World*Health.*** *Strengthening*Specialised*Clinical*Services*in*the*Pacific.*User*Care*of*Medical*Equipment:*A*first*line*maintenance*guide*for*end*users.*(2015).****WHO.*“Quality*Control*For*Autoclaves.”*From*the*publication:*Laboratory*Equipment*Maintenance*Manual,*WHO:*2008.* *** *

Knowledge Domain: Plumbing
Unit: Blockages
Skill: Descaling

Tools and Parts Required:

1) Vinegar
2) Autoclave, sterilizer, or hot water pot with mineral buildup
3) Nylon scouring pad (optional)
4) Mineral free (distilled) water


Equipment that uses water may accumulate mineral buildup. Minerals are corrosive to
stainless steel. Mineral buildup will reduce the efficiency and lifespan of the equipment.
Regular removal of mineral buildup will extend the life of the equipment. Mineral
buildup can also prevent adequate sterilization.


Below is a picture of an autoclave with mineral buildup (sometimes called scale).

Descaling to Remove Mineral Buildup


EWH. “Descaling to Remove Mineral Buildup.”

Identification and Diagnosis

Scale is an accumulation of minerals such as calcium on the surface of a device. Scale
is different from rust (see BTA skill on “cleaning rust”). Thick scale can sometimes be
scraped off. Scale can be white or gray. Contaminants determine the color of the
scale. Scale may appear as flakes as shown below. Some scale may look like a thin
film covering surfaces that have been exposed to water.


Before working on any medical equipment, ensure that the device has been
disconnected from electricity.

Autoclaves become very hot during use. Avoid burns by ensuring the machine is not
hot before touching any surfaces.

Begin by scraping any excess scale or contaminants. Use a cloth to wipe off loose
contaminants and dirt. A plastic scouring pad can be used for more vigorous scrubbing.

Usually, you will need a solvent to remove scale. Some manufacturers suggest specific
products for cleaning sterilizers and autoclaves. A mild acid such as vinegar or lemon
juice is a good substitute.

Below is a picture of glass bottle with mineral buildup. Vinegar was used to remove the



EWH. “Descaling to Remove Mineral Buildup.”

For optimal performance, sterilizers and autoclaves should be cleaned once a week.

Mix the descaling solvent according to the manufacturer’s directions. When using
lemon juice or vinegar, use 1 part vinegar and 1 part mineral free (distilled) water.

Drain water from the reservoir of the autoclave. Fill with descaling solvent. Run a
complete sterilization cycle. When descaling a single container, let the solvent sit for at
least 30 minutes. Do not attempt to sterilize any equipment while descaling.

After the descaling is complete, drain the solvent. Rinse the system with mineral free
water for at least 15 minutes. Do not sterilize any equipment until all solvent has been

Sometimes a mild solvent is not strong enough to remove scale. In some cases you
must use muriatic acid (also known as hydrochloric acid), a very strong acid. Always
wear gloves and eye protection when using muriatic acid. Dilute muriatic acid with 1 part
acid to 20 parts water. Pour the acid carefully into water to avoid splashes. Apply the
solution to the scale. Bubbles indicate that the solution is strong enough. Run water
over the area to rinse thoroughly after cleaning. Do not allow acid to come into contact
with skin or eyes.

Detergents containing chlorine are corrosive to steel. Do not use detergents containing
chlorine to remove scale.


Removing scale requires the presence of scale. During your hospital visits, your
instructor may point out an autoclave or sterilizer with mineral buildup. You may have
the chance to remove the scale.

Check hot water pots and kettles for mineral buildup. Use the described procedure to
remove the scale.

Removing Scale

Soaking with

After Cleaning


Your instructor must verify your work before you continue.

Preventative Maintenance and Calibration

Use mineral free water to prevent build up of scale.

Acids can be dangerous to the skin. Always use protective gloves and work in a well
ventilated area.

Always calibrate every medical device before returning it to use.


EWH. “Descaling to Remove Mineral Buildup.”


• After each use: Clean the inside of the autoclave and around valve and vents o Empty all water from chamber and thoroughly dry o Wipe off metal-to-metal seal with clean towel to remove build-up • Make sure valves are not clogged o Periodically clean control valve with hot, soapy water • Check air exhaust tube by flushing water through it to make sure it is not blocked. • Descale'the'chamber:'most'effective'to'use'detergent'meant'for'lime'scale'removal.'Vinegar'diluted'with'distilled'water'can'also'be'used.'• Check for signs of wear and damage. Ensure sufficient seal around lid: o For a metal-to-metal seal, lubrication of the seal must be maintained o For a gasket seal, the seal must be pliable. If it is cracked or dry, then it should be replaced • Valve safety check: Test the safety pop-off any time there is pressure built up in the sterilizer. Test the valve below the operating pressure with the use of a screwdriver to pop the pressure relief valve. Make sure your hand is away; otherwise the steam can cause burns.


Cooper, Justin and Alex Dahinten for EWH. “Autoclave Preventative Maintenance.”

From the publication: Medical Equipment Troubleshooting Flowchart Handbook.

Durham, NC: Engineering World Health, 2013.

User Care of Medical Equipment – First line maintenance for end users


User Care Checklist – Autoclaves / Sterilizers



9 Remove any dust / dirt with damp cloth and dry off

9 Remove water and waste matter from inside

Visual checks

9 Check all screws, connectors and parts are tightly fitted

9 Check all moving parts move freely, all holes are unblocked


9 Use troubleshooting guide if problems occur



9 Unplug, clean inside and outside with damp cloth and dry off

9 Remove gasket, clean with a damp cloth and replace

Visual checks

9 Scrape off any small deposits of limescale

9 Send for repair if heating element covered with limescale

9 If plug, cable or socket are damaged, replace


9 When next used, check pressure / temperature gauges rise

9 When next used, check there are no leaks

Every six months
Biomedical Technician check required



c) Once these conditions are attained, the countdown
for completing the sterilization (depending on the
type of objects or materials being processed) is
initiated. The higher the temperature and pressure,
the lesser the time required for sterilizing.

d) Once the programmed sterilization time has
ended, post treatment process is initiated. This
includes depressurization of the chamber normally
done with the help of the exhaust and drying
system using the supply of heat transferred from
the jacket to the sterilization chamber. Upon
decreasing the pressure, the required temperature
for evaporating any liquid residue that may have
formed on objects during depressurization is
attained. A vacuum of 10 % of the atmospheric
pressure is created and maintained steady for
a period of time. When liquids are sterilized, no
vacuum is created; rather, vapour extraction is
controlled through a restrictive mechanism to
prevent boiling inside the containers autoclaved.

e) Finally, controlled entry of air through valves with
high efficiency filters will be allowed until the
pressure in the sterilization chamber is equal to
the atmospheric pressure. The sterilization cycle
has ended.

7. Open the door of the autoclave.
8. Unload the sterilized material.
9. Close the door once the sterilized material is unloaded

to conserve the heat in the sterilization chamber and
facilitate the next sterilization cycle.

10. Store the sterilized material appropriately.

Note: The sterilization cycles must be supervised and
submitted to quality control procedures through the use
of physical, chemical and biological type indicators for
ensuring their eff ectiveness.

Warning: Not all objects can be sterilized with moist heat.
Some require sterilization procedures at low temperature.
Verify which procedure must be used according to the type
of material to be sterilized.

Sterilization cycles
The sterilization processes follow predefined cycles
according to the type of load to be sterilized. There are
diff erent sterilization cycles for porous materials, surgical
instruments, liquids or heat sensitive material. The main
ones known as clinical sterilization cycles are carried out
under the following conditions: 121 °C / 1.1 kg /cm2 or
134 °C / 2.2 kg /cm2. Their main characteristics are featured
in the table on the next page.

Note: The sterilization cycle times are adjusted to the
altitude where the autoclave is located. Manufacturers
supply compensation tables to be taken into account. In

general, the higher the altitude of the equipment’s location,
the longer the sterilization time will be.

Quality Control
In order for a product to be considered sterilized, it is
necessary to verify that all the stages of the sterilization
process have been carried out correctly. To verify that these
have been fulfi lled, a series of tests have been developed
to evaluate the characteristics of the process and its
infl uence on the activity of microorganisms. Evaluations
of the temperature, pressure, time, humidity and general
equipment behaviour are carried out to certify that it
complies with, and functions according to procedures that
demonstrated its validity and reliability. There are also tests
or indicators that allow the death of the microorganisms
to be certifi ed in order to guarantee the quality of the
sterilization processes. Diff erent categories of tests have
been developed. Some are featured next:
1. Sterilization process indicators. These are designed

for supervising the functioning of the autoclaves.
They include instruments that control parameters
like temperature, time and pressure (thermometers,
manometers and chronometers) and register the
development of the process. The registering systems
of modern autoclaves (microprocessor) register all
the parameters of the sterilization cycle and also halt
the cycle in case some anomaly occurs. There is also
the Bowie-Dick test in this category: it evaluates the
effi ciency of the exhaust pump using a test sheet which
changes in colour uniformly if the process has been
completed satisfactorily. If it is not the case, the colour
of the sheet is uneven.

2. Chemical indicators. These are typical chemical
tests changing colour or state when exposed to the
diff erent phases of the sterilization process. Chemical
indicators allow the diff erentiation of articles submitted
or exposed to a successful sterilization process from
those that have not. Among the best known are the
adhesive tapes or strips that go inside a component or
on packages. The ISO Nº 11140-1 standard describes
categories of chemical indicators. One has to keep in
mind that chemical indicators by themselves do not
guarantee that the sterilization process complied with
all the requirements: personnel who use these must
receive precise training to allow them to determine if
the result obtained is coherent with the evolution of the
whole sterilization process.

3. Biological indicators. These are considered the best
methods for controlling the quality of a sterilization
process. They are made of live microorganisms which
have a greater resistance to a determined sterilization
process, or of chemical reagents which react in the
presence of the specifi c proteins of this type of organism.
In order to control the sterilization process by saturated
vapour, (hydrogen peroxide) or formaldehyde, spores

Quality Control for Autoclaves


WHO. “Quality Control For Autoclaves.” From the publication: Laboratory Equipment Maintenance Manual, WHO: 2008.

C H A P T E R 1 2 A U TO C L AV E S


Cycle no. M aterials Temp. ˚C Pressure kg/cm 2 Typic al graph

1 • Porous loads
• Tex tiles
• Wrapped

• Tubes

135 2.2

2 • Open

• Utensils
• Glasswa re
• Open containers

135 2.2

3 • Heat sensitive

• Rubber
• Plastic

121 1.1

4 • Liquids in open
or semi- closed

121 1.1

Convention A: Pre -treatment. Alternate c ycles of injec tion / vacuum of vapour.
Pre -treatment. (Processes 1, 2, 3).
Process 4: Sterilization.
C: Post-treatment (Process 5: vacuum and dr ying).
D: Internal and ex ternal pressures completely mixed.
Note: The liquid process does not have vacuum after sterilization. The cooling is natural.

1 The graphs included correspond to an autoclave with an emptying pump, Getinge brand GE-660 autoclave.
(*) Times depend on the volume of the load. There is no vacuum during cooling.






(-) A

1 2 3 5

135o C, 7 min

< 50 mb, 5 min










1 2 3 5

135o C, 4 min

< 50 mb, 2 min




< 50 mb, 5 min








521 3

121o C, 20 min


121o C, 20 minTime










WHO. “Quality Control For Autoclaves.” From the publication: Laboratory Equipment Maintenance Manual, WHO: 2008.




of Bacillus stearothermophilus are generally used. To
control sterilization by dry heat (a process that drying
ovens perform) and by ethylene oxide, spores of the
Niger variety of Bacillus subtilis are used. The spore
indicator is placed in the sterilizing load. After the
process, it is incubated, analyzed and it is determined
if the cycle meets with the sterilization requirements.
Generally a change of colour is observed. These tests
are standardized and manufacturers indicate how to
use them and interpret the results. Biological indicators
by themselves do not guarantee that the sterilization
cycle complies with all the requirements. The only way
to do this is by controlling all the sterilization cycle’s

Frequency of the quality control processes
A table summarizing the suggested frequency with regard
to the use of quality control indicators in the sterilization
processes is shown next.

To be able to function, autoclaves require the following

A well ventilated area for removing heat and humidity
generated while in operation. It also requires free space
around the back and sides, to accommodate technical

servicing. This space should be at least 0.8 m. Depending
on the design of the autoclave, complementary
infrastructure must be anticipated so that it can operate
satisfactorily. The diagram in Figure 33 explains the
space required around the autoclave. The temperature
in the immediate vicinity of the equipment may increase
to more than 70 °C when it is in operation. The fl oor
should be well levelled and constructed with materials
resistant to humidity and heat.

2. An electrical outlet in proportion to the equipment’s
consumption. If the autoclave is autonomous, meaning
that it has its own vapour generator, the electrical
connection must be studied in detail as the required
power could be significantly higher. Typical power
demands are 21, 38, 48 kW and higher, for the vapour
generator to function. The connection must be equipped
with required safety and protection elements. The
typical voltages required for autoclaves are 220 V, 60
Hz, or 380 V, 60 Hz triphase.

3. Water connection proportional to the equipment’s
consumption in volume and pressure: the larger the
equipment, the greater the consumption. The water
which the autoclave consumes must have received
required treatments for eliminating solids in suspension
as these may negatively aff ect the functioning of the
electrovalves as well as that of the electro hydraulic

4. Some sterilizers require compressed air, as their controls
are managed by pneumatic pressure. In general, the
required pressure varies from 5x10 5 to 9.9x105 Pa. The
following diagram shows the minimum installation
requirements (cut-off valve, fi lter and manometer).

5. A drainage system designed for collecting hot water.
6. A vapour connection. If the autoclave does not have

its own vapour generator, it must be fed from the
institution’s vapour generating system (machine room,
boiler). The supply installation must meet the necessary

Type of indic ator Frequenc y of use
Process In each sterilization c ycle.
Chemical In each packag e.
Biological Weekly, in all the sterilization equipment; in the

packets that contain implants.


Figure 33. Space required for autoclave


Figure 34. Compressed air connection


WHO. “Quality Control For Autoclaves.” From the publication: Laboratory Equipment Maintenance Manual, WHO: 2008.

WHO. “Quality Control For Autoclaves.” From the publication: Laboratory Equipment Maintenance Manual, WHO: 2008.

C H A P T E R 1 2 A U TO C L AV E S


requirements: a cut-off valve, fi lter, manometer as well as
an appropriate installation for collecting the condensed
liquid with a fi lter and vapour trap, as indicated in the

Figure 35.

6. The autoclave must be operated exclusively by
personnel specially trained and qualifi ed in these types
of processes.

The autoclave is equipment which demands supervision
and continuous preventive maintenance due to its multiple
components and systems. Maintenance is focused on the basic
routines that can be performed by the operators. In order to
carry out detailed maintenance, the instructions described in
the manufacturer’s service manuals must be followed.

Daily verifi cations
Before initiating the sterilization processes, the following

verifi cations will have to be carried out:
1. Place a new form on the registration device in order to

document the development of the sterilization cycle.
2. Ensure that the cycle-recording pen or that the printing

module of the autoclave has ink and recording paper.
3. Ensure that the cold water, compressed air and vapour

supply valves are open.
4. Activate the switch that triggers the autoclave’s jacket

heating. Upon activating this control, vapour is allowed
to enter the sterilization chamber’s jacket. When vapour
enters the sterilization chamber, the heating process
begins. To avoid heat loss, keep the autoclave’s door
closed until it is time to add the load for sterilization.

5. Verify that the pressure from the vapour supply line is
at least 2.5 bar.

6. Test the condition of manometers and thermometers.
7. Ensure that there are no vapour leaks in any of the

systems functioning in the autoclave.
8. Clean the front of the autoclave, controls, indicators and

handles with a damp cloth.
Weekly maintenance
Responsible: The equipment operator
1. Clean the sterilization chamber drainage fi lter. Remove

any residue retained inside.
2. Clean the inside of the sterilization chamber using

cleaning products that do not contain chlorine. Clean
the guides used for placing the baskets as well.

3. Clean with an acetifi ed solution, if solutions with chlorine
are being sterilized. The chlorine causes corrosion even
on stainless steel implants. Next, wash with plenty of

4. Clean the external rust-proof surfaces with a mild
detergent. A solvent like ethylene chloride can be used,
avoiding touching any surface with painted coverings,
markings or plastic coverings.

5. In autoclaves with manually activated doors, verify
that these mechanisms are well adjusted and that their
operation is smooth.

6. Drain the vapour generator (if the equipment has one).
To do this, open a valve located on the lower part of
the generator which allows its contents to be drained.
Generally this is done at the end of weekly activities.
Follow the manufacturer’s recommendations.

7. Never use steel wool for cleaning the inside of the
sterilization chamber.

8. Check adequate functioning using a biological or
chemical indicator. To check the temperature, use
chemical test strips checking time and temperature of
exposure sold for this purpose.

Quarterly maintenance
Responsible: The autoclave technician
1. Check that the manometers function as expected.
2. Activate the safety valves manually to verify that they

are operating well. Use a large screwdriver to move
the activation lever normally located in the upper part
of the valve. Make sure that the face and body of the
operator are not in the vapour’s path. Once the valve is
activated, ensure that there are no vapour leaks. If there
are any leaks, the valve must be activated again until it
is well sealed.

Warning: If vapour leaks are not eliminated, this will
deteriorate the seal rapidly and the whole safety valve
system will have to be replaced.

3. Lubricate the door’s gasket. Use the lubricant and
the procedure recommended by the equipment’s
manufacturer. Some manufacturers recommend the
following procedure:
a) Remove the gasket. To do this, it is necessary to

dismount from the groove, loosening the retention
mechanisms (screws and plates).

Cut-0ff Valve


To the Autoclave

Vapour Connection


Vapour Trap
Alternative Floor Level Vapour Connection

Figure 35. Vapour connection


WHO. “Quality Control For Autoclaves.” From the publication: Laboratory Equipment Maintenance Manual, WHO: 2008.



b) Clean the gasket and the groove with alcohol so that
there is no foreign material to aff ect the seal. The
surface of the gasket must stay smooth and clean.

c) Apply the lubricant recommended by the
manufacturer to the body of the gasket until
it is completely protected. Many autoclave
manufacturers use graphite lubricant resistant to
high temperatures.

d) Reinstall the gasket. In rectangular chamber
autoclaves, this is normally installed placing
the gasket in the middle of one of the assembly
groove’s sides and adjusting the remaining portion
towards the sides, until it is well adjusted inside the
groove. The same procedure is repeated for each
remaining side. In round chamber autoclaves, the
gasket assembly begins on the upper part and is
adjusted progressively into the groove without
pulling it, until the whole gasket is installed. Next,
assembly elements are adjusted.

4. Verify that the seals of the safety valves are in good

5. Clean the points of the registration pen system with
water or alcohol and restore the ink levels. Generally, the
pressure is registered with red ink and the temperature
with green.

6. Clean the inside of the vapour generator (for equipment
with this accessory). For the vapour generator, the
cleaning procedure involves carrying out the following
a) Disconnect the electrical supply to the

b) Discharge the vapour pressure and wait for the

equipment to reach room temperature.

c) Remove the front cover of the generator.
d) Disconnect the electrical terminals of the heating

resistors (immersion).
e) Remove the screws that secure the front plate

where the heating resistances are installed and
dismount the front plate.

f ) Check the gasket and substitute it if necessary.
g) Remove dirt accumulated on the surface of the

heating resistors. Use products recommended1.
h) Re-assemble in the reverse order.

Figure 36 shows the vapour generator and its components.

Annual maintenance
Responsible: The autoclave technician
1. Clean all the fi lters.
2. Test and adjust the water level of feed tank so that it is

within 20 mm of the maximum level.
3. Verify and adjust the tension of diaphragm valves’

4. Dismount, clean and adjust the safety valves.
5. Change the air fi lter.
6. Conduct a general sterilization process testing in

detail the pressure, temperature, required times for
completing each phase of the cycle, state of the process’
signal lamps and functioning of the registration system.
Verify that it is functioning within tolerances defi ned by
the manufacturer.

7. Perform the quarterly routines.

1 Incrustations are seen when the water used by the vapour generator has
not received adequate treatment.

Water Level Control

Resistor Terminals

Flange Mounted Resistors

Vapour Exit Line


Immersion Resistances

Vapour Generator Cover

Water Feed Line

Vapour Generator Drainage Line

Figure 36. Vapour generator


WHO. “Quality Control For Autoclaves.” From the publication: Laboratory Equipment Maintenance Manual,

WHO: 2008.

C H A P T E R 1 2 A U TO C L AV E S


Included next are some specialized routines requiring
a service technician and applicable to equipment
components. Given that autoclaves have multiple designs,
routines stipulated here are only applicable to certain
equipment models.

Maintenance of solenoid valves
1. Verify the sound made by the bobbins or solenoids

(humming ). Excessive noise is a warning of overheating
due to abnormally high electric currents through the
solenoid. Current alternates rise when the impedance [Z]
of the circuit decreases. This occurs when the solenoid
is not adequately surrounded by a closed iron cover.
An air gap in the magnetic circuit can be caused by dirt
which prevents the protective cover from reaching its
fi nal position when the solenoid is energized. Carefully
clean the housing of the bobbin and its nucleus so that
the piston’s movement is not impeded by fi lth.

2. Replace the O-rings between the solenoid and the body
of the valve once these have been disassembled.

3. Before any disassembly, verify how the solenoid valve
is installed. Some possess clear installation indications
but others lack such information.

4. When dismounting a servo-assisted solenoid valve,
control the position of the orifi ces that put it in contact
with the work environment, so as to be able to re-
assemble the valve.

Cleaning of the vapour fi lter

Warning: Before disassembling the vapour fi lter, dissipate
the vapour pressure in the system.

1. Lift the cover.
2. Remove the mesh.
3. Clean carefully.
4. Reinstall the mesh.
5. Replace the cover.

Here are some of the most common problems. Given the
diversity of brands, models and available technology, it
is advisable that users follow instructions from the user
manual for the autoclave used.


WHO. “Quality Control For Autoclaves.” From the publication: Laboratory Equipment Maintenance Manual,

WHO: 2008.



! !

Cooper, Justin and Alex Dahinten for EWH. “Autoclave Troubleshooting Flowchart.” From the

publication: Medical Equipment Troubleshooting Flowchart Handbook. Durham, NC: Engineering World

Health, (2013).

Description*#* Text*Box* Comments*
1! Begin:!Autoclave! Start!the!diagnostic!process!for!a!work!order!on!an!autoclave!
2! Does!the!indicator!lamp!illuminate?! Provide!appropriate!power!supply!to!the!autoclave!and!observe!indication!that!the!device!turns!on!
3! Troubleshoot!power!supply! If!the!device!is!connected!to!power!but!does!not!turn!on,!there!is!a!problem!with!the!power!supply.!This!could!be!a!problem!with!the!wiring!or!connections!within!the!device.!See!BTA!skills!on!Power!Supply!
4! Is!voltage!across!heating!element!equal!to!the!expected!value?! Use!a!multimeter!to!test!the!wires!leading!to!the!heating!element!to!determine!if!it!is!receiving!the!expected!voltage!(wall!voltage)!
5! Troubleshoot!control!circuitry! If!the!device!is!receiving!power!but!improper!voltage!is!reaching!the!heating!element,!there!is!likely!a!problem!with!the!control!circuit.!Ensure!that!all!settings!are!what!they!should!be!for!normal!autoclave!function!
6! Does!the!heating!element!warm!up?! Attach!autoclave!to!power!with!lid!open!and!observe!whether!the!heating!element!begins!to!get!hotter!
7! Look!for!rusted!or!cracked!connections! Examine!connections!involved!with!the!heating!element!to!determine!whether!they!are!adequate!for!proper!functionality!
8! Clean/Mend!poor!connections! See!BTA!skills!on!Connections!
9! Is!the!resistance!across!the!heating!element!less!than!20!Ohms?! Use!a!multimeter!across!the!heating!element!to!determine!its!total!resistance!
10! Replace!heating!element!if!necessary! If!the!resistance!across!the!heating!element!is!greater!than!20!Ohms,!it!needs!to!be!replaced.!To!replace!the!wire!within!the!element,!nichrome!wire!must!be!used.!See!BTA!skills!on!Heating!Element!
11! Do!temp!and!pressure!gauge!needle(s)!move?! While!autoclave!runs!cycle,!observe!motion!of!temperature!and!pressure!gauge(s).!There!must!be!displayed!values!for!BOTH!parameters!to!advance!from!this!step!
12! Does!temperature!gauge!remain!at!zero?! Determine!if!value!of!zero!is!given!for!temperature!despite!temperature!increase!
13! Does!pressure!gauge!remain!at!zero?! Determine!if!value!of!zero!is!given!for!pressure!when!pressure!is!expected!to!have!increased!


Cooper, Justin and Alex Dahinten for EWH. “Autoclave Troubleshooting Flowchart.” From the

publication: Medical Equipment Troubleshooting Flowchart Handbook. Durham, NC: Engineering World

Health, (2013).

14! Clean!gauge!vent! If!the!gauge!works!but!does!not!move!during!autoclave!cycle,!then!the!vent!leading!to!the!gauge!input!may!be!blocked.!Flush!vent!with!distilled!water!to!remove!blockage.!CAUTION:!do!not!submerge!gauge!in!water.!See!BTA!skills!on!Blockage!
15! Inspect!gauge!components!

16! Clean!gauge!vent! If!the!gauge!works!but!does!not!move!during!autoclave!cycle,!then!the!vent!leading!to!the!gauge!input!may!be!blocked.!Flush!vent!with!distilled!water!to!remove!blockage.!CAUTION:!do!not!submerge!gauge!in!water.!See!BTA!skills!on!Blockage!
17! Inspect!gauge!components!

18! Inspect!autoclave!for!leaks! Examine!all!parts!of!autoclave!to!find!any!leaks.!Visually!inspect!for!steam!escaping!from!autoclave.!See!BTA!skills!on!Leaking!
19! Replace!gauge(s)!is!necessary! If!the!gauge!needle!cannot!be!made!to!move!as!described!in!#15!and!#17,!then!the!gauge!is!likely!broken!and!may!need!to!be!replaced!
20! Do!temperature!and!pressure!reach!required!values?!

21! Are!measured!values!too!low?! Determine!if!the!autoclave!reaches!temperature!and!pressure!values!below!those!required!for!sterilization!by!reading!the!gauge!values.!
22! Are!measured!values!too!high?! Determine!if!the!autoclave!reaches!temperature!and!pressure!values!above!those!required!for!sterilization!by!reading!the!gauge!values.!
23! Check!valves!for!leaks! Visually!inspect!closed!valves!throughout!cycle.!If!air!escapes!closed!valve,!then!there!is!a!leak!in!the!valve!that!must!be!mended.!See!BTA!skills!on!Leaking!
24! Check!valve!mechanisms! Check!functionality!of!valve!components!by!ensuring!that!they!are!able!to!open!and!close!smoothly!
25! Check!valve!connections!and!lid/door!seal!for!leaks! Examine!points!at!which!valves!connect!to!autoclave!to!ensure!that!they!are!adequately!sealed!If!autoclave!door/lid!has!a!metalctocmetal!seal,!lubricate!seal!


Cooper, Justin and Alex Dahinten for EWH. “Autoclave Troubleshooting Flowchart.” From the

publication: Medical Equipment Troubleshooting Flowchart Handbook. Durham, NC: Engineering World

Health, (2013).

26! Check!inlet/outlet!tubing!for!leaks! Visually!examine!autoclave!tubing!for!leaks.!See!BTA!skills!on!Leaking!
27! Check!valves!and!exhaust!tubing!for!blockages! Open!valves!and!ensure!that!air!can!pass!through!them.!Also!verify!that!exhaust!tubing!is!unobstructed.!See!BTA!skills!on!Blockages!
28! Clear!blockages!by!flushing!with!water! If!any!blockages!are!found,!flush!the!blocked!components!with!distilled!water!to!remove!blockages.!See!BTA!skills!on!Blockage!
29! Check!inlet/outlet!filters!for!clogs! Examine!autoclave!filters!for!clogs.!If!clogs!are!found,!clean!or!replace!filter(s).!See!BTA!skills!on!Filters!
30! Are!temperature!and!pressure!values!maintained!for!required!amount!of!time?!

31! Adjust!time!controls! Ensure!that!time!is!on!correct!setting!Common!times:!121˚C!for!15!minutes,!134˚C!for!3!minutes!
32! Troubleshoot!timing!circuit!

33! Do!temperature!and!pressure!decrease!after!cycle?!

34! Check!valves!and!exhaust!tubing!for!blockages!

35! Troubleshoot!timing!circuit!

36! If!autoclave!tape!is!available,!do!strips!confirm! Run!test!cycle!with!autoclave!test!tape!to!verify!that!sterilization!is!achieved.!If!tape!is!not!available,!biological!indicators!can!also!be!used!for!


Cooper, Justin and Alex Dahinten for EWH. “Autoclave Troubleshooting Flowchart.” From the

publication: Medical Equipment Troubleshooting Flowchart Handbook. Durham, NC: Engineering World

Health, (2013).

sterilization?! sterilization.!
37! Consider!replacing!autoclave! Autoclave!may!be!beyond!repair.!Discontinue!autoclave!use!or!refer!to!specialist!!Note!about!autoclave!tape:!

• Autoclave! tape! is! an! adhesive! used! to! indicate!whether! a! specific! temperature! and! pressure! have!been!reached!
• Strips!of!this!tape!are!applied!to!items!before!they!are!placed!into!the!autoclave!
• The!tape!has!diagonal!markings!that!will!change!color!when!the!target!temperature!and!pressure!are!achieved!
• If! the! tape!markings! are! still! their! original! color! after! going! through! the! autoclave! cycle,! then! the!autoclave!did!not!reach!the!temperature!and!pressure!required!for!sterilization!
• Biological!indicators!can!be!used!to!monitor!the!sterilization!of!an!autoclave,!by!testing!its!capability!to! kill! microorganisms.! Only! Bacillus( stearothermophilus! spores! can! be! used! to! monitor! the!effectiveness!of!steam!autoclaves.
• A! biological! indicator! system! consists! of! the! growth!medium!with! spores! and! indicator! dye.! After!autoclaving!the!indicator,! it!has!to!be!incubated!at!56°C!for!up!to!three!days.!Any!signs!of!turbidity!(indicating!growth)!indicate!the!autoclave!did!not!function!properly.!!


Cooper, Justin and Alex Dahinten for EWH. “Autoclave Troubleshooting Flowchart.” From the

publication: Medical Equipment Troubleshooting Flowchart Handbook. Durham, NC: Engineering World

Health, (2013).

User Care of Medical Equipment – First line maintenance for end users


Troubleshooting – Autoclaves and Sterilizers

Fault Possible Cause Solution


Equipment is not heating

No power at mains socket

Electrical cable fault

Damaged heating element

Check power switch is on.
Replace fuse with correct voltage and current
rating if blown.
Check mains power is present at socket using
equipment known to be working. Contact
electrician for rewiring if power not present.

Try cable on another piece of equipment.
Contact electrician for repair if required.

Send to electrician if broken or covered in
limescale (see picture below). Remove small
amounts of limescale by light scraping and
long soaking in distilled water.


Pressure rises above the
marked level

Blocked valve

Clean the pressure regulating valve, safety

Pressure vessel may be over filled.

Retest autoclave under pressure with water


Steam is constantly escaping

Poor seal

Clean leaky valve and hole, replace if

Clean leaking seal or gasket, replace if broken.


Electrical shocks

Wiring fault

Refer to electrician

Limescale on heating element

5.*Resources*for*More*Information******Featured*in*this*Section:*****DHT*Laboratory,*“Sealing*Autoclave*Doors.”*From*the*publication:*Biomedical*Technician*Assistant*(BTA)*Skills.*Developing*World*Healthcare*Technology*Laboratory:*Duke*University,*2011.****Fear,*D.*and*Skeet,*M.*“Autoclaves.”*From*the*publication:*Care*and*Safe*Use*of*Medical*Equipment.*VSO*Books,*1995.* **National*Biosafety*and*Biocontainment*Training*Program,*National*Institute*of*Health,*and*Dartmouth*College.*“Autoclave*Safety:*The*Proper*Use*of*an*Autoclave*to*Decontaminate*Biohazardous*Waste.”*May*11,*2011.*Retrieved*from:*****

Resources*for*More*Information: ***Internal*Resources*at**For*more*information*about*autoclaves,*please*see*this*resource*in*the*BMET*Library!***1.*DHT*Laboratory,*“Sealing*Autoclave*Doors.”*From*the*publication:*Biomedical*Technician*Assistant*(BTA)*Skills.*Developing*World*Healthcare*Technology*Laboratory:*Duke*University,*2011.**2.*Fear,*D.*and*Skeet,*M.*“Autoclaves.”*From*the*publication:*Care*and*Safe*Use*of*edical*Equipment.*VSO*Books,*1995.**External*Resources:**2.*Autoclave*Safety*Videos:**These*videos*created*by*the*National*Biosafety*and*Biocontainment*Training*program*and*Dartmouth*University*explain*how*to*safely*operate*an*autoclave.*This*video*demonstrates*the*path*of*energy*through*an*autoclave,*labels*autoclave*parts,*and*provides*safety*tips.*This*video*is*available*in*eight*languages.**"Autoclave+Safety:+The+Proper+Use+of+an+Autoclave+to+Decontaminate+Biohazardous+Waste.”*National*Biosafety*and*Biocontainment*Training*Program,*National*Institute*of*Health,*and*Dartmouth*College.*Posted*May*11,*2011.*** 1. Autoclave*Safety*(English):**2. Autoclave*Safety*(Chinese):**3. Autoclave*Safety*(Arabic):**4. Autoclave*Safety*(French):**5. Autoclave*Safety*(Russian):**6. Autoclave*Safety*(Spanish):*********

Autoclave*Bibliography:*****Cooper,*Justin*and*Alex*Dahinten*for*EWH.*“Autoclave*Preventative*Maintenance.”*From*the*publication:**Medical*Equipment*Troubleshooting*Flowchart*Handbook.*Durham,*NC:*Engineering*World*Health,*2013.***Cooper,*Justin*and*Alex*Dahinten*for*EWH.*“Autoclave*Troubleshooting*Flowchart.”*From*the*publication:*e*Medical*Equipment*Troubleshooting*Flowchart*Handbook.*Durham,*NC:*Engineering*World*Health,*(2013).***DHT*Laboratory,*“Sealing*Autoclave*Doors.”*From*the*publication:*Biomedical*Technician*Assistant*(BTA)*Skills.*Developing*World*Healthcare*Technology*Laboratory:*Duke*University,*2011.***Discover*Biotech.*“Physical*Means*of*Microbial*Control.”*Retrieved*from:**** EWH.*“Descaling*to*Remove*Mineral*Buildup.”*Engineering*World*Health.***Malkin,*Robert.*Medical*Instrumentation*in*the*Developing*World.*Engineering*World*Health,*2006.****Fear,*D.*and*Skeet,*M.*“Autoclaves.”*From*the*publication:*Care*and*Safe*Use*of*Medical*Equipment.*VSO*Books,*1995.***National*Biosafety*and*Biocontainment*Training*Program,*National*Institute*of*Health,*and*Dartmouth*College.*“Autoclave*Safety:*The*Proper*Use*of*an*Autoclave*to*Decontaminate*Biohazardous*Waste.”*May*11,*2011.*Retrieved*from:**********

**Autoclave*Bibliography:***Strengthening*Specialised*Clinical*Services*in*the*Pacific.*User*Care*of*Medical*Equipment:*A*first*line*maintenance*guide*for*end*users.*(2015).***WHO.*“Troubleshooting*Table.”*From*the*publication:*Laboratory*Equipment*Maintenance*Manual,*WHO:*2008.***WHO.*“Quality*Control*For*Autoclaves.”*From*the*publication:*Laboratory*Equipment*Maintenance*Manual,*WHO:*2008.***Wikipedia.*“Sterilization*(Microbiology).”*Wikipedia,*p.*1d12.*Retrieved*from:*** *

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