AUTOCLAVE VALIDATION – WHAT IS REALLY REQUIRED?
Guy Snelling
PO Box 10907 Vorna Valley 1686
[email protected]
Abstract
Steam autoclaves have been with us for many
years and are used in many different industries.
Their primary task is to sterilize items so that
these same items can be used in situations
where the introduction of micro-organisms
would pose a health-risk. But how can we be
sure that the autoclave is doing its job?
Biological indicators form part of this validation,
but there are many tests that should be
performed regularly. This paper describes
these tests, and how often they should be
performed in order for the user to be confident
that their autoclave is functioning properly and
within the requirements of the regulatory
bodies.
Introduction
There are four general types of sterilizers
namely, Gamma Irradiation, Gas Sterilization,
Dry Heat and Moist Heat. Whilst validation of
all types of sterilizers follows the same basic
principles, by far the most prevalent type in
South Africa are steam or moist heat
autoclaves and this paper therefore deals
specifically with this type.
Method of Operation
Steam autoclaves generally follow the
principles shown in Figure 1. Water is heated
and the steam pressure is built up in the jacket.
Once sufficient pressure is obtained, the steam
is allowed to enter the chamber, thereby driving
the air out of the drain port. Once all the air
has been replaced by steam, the drain valve
closes and steam pressure builds up in the
chamber. The resultant pressure causes the
temperature in the chamber to rise to the
required point, usually 121 or 135 °C.
Some type of autoclaves have a vacuum
function that pumps out the air before the
steam is allow to enter. This method is much
faster and more efficient.
Figure 1
Diagram of a horizontal steam autoclave
An alternative method is used in vertical
autoclaves. See figure 2. Water is placed in
the bottom of the chamber and heated by an
electrical element. The resulting steam drives
the air out of an evacuation port near the top of
the chamber. Again the evacuation port is
closed once all the air has been removed and
the steam pressure is allowed to build.
Evacuation
valve
Steam
Element
Figure 2 Diagram of vertical autoclave
Cycles Stages
Generally an autoclave cycle consists of 3
stages viz. heating, sterilizing, de-pressure.
Vertical autoclaves may have a “water fill”
stage before the heating stage. Autoclaves
fitted with vacuum facility may have vacuum
stages before the heating stage and also as
part of the depressurizing stage.
Load Types
Autoclaves are used
different types of loads:
to
sterilize
several
Solid – metal, glass, plastic
Porous – linen, gowns, paper, gauze,
complex instruments, hollow tubes
Liquid – water, saline, media
Laboratory waste – Petri dishes,
sample bottles, syringes
[1]
Heating Sterilizing Depressure Complete
There are various methods of validation,
depending on the usage of the autoclave.
Instrumentation
Figure 3 Typical autoclave cycle
Why Validate?
The instrumentation fitted to an autoclave will
vary depending on the complexity and price of
the autoclave. A vertical autoclave may only
be fitted with a pressure gauge (also marked
in °C) and a pressure regulator. A more
complex, fully automated large autoclave may
have a computer controlled display showing
various temperature and pressures throughout
the workings of the autoclave. Typically though,
jacket pressure and chamber pressure would
be indicated, along with chamber temperature.
Validation requires that these instruments be
checked for accuracy.
System supplies
Most autoclaves are electrically powered and
all steam autoclaves require some form of a
water supply to produce steam. The electrical
supply must be able to handle the maximum
peak power of the autoclave. The quality of the
water supply will affect the quality of the steam
Figure 4 Temperature and Physical Control of
Microorganisms
As can be seen from Figure 4, if the
temperature in an autoclave does not reach
121 °C, not all spores will be destroyed in the
typical cycle time of 20 minutes. Validation is
therefore required to ensure that the autoclave
is operating correctly and that complete
sterilization is being achieved.
The drainage system must be able to handle
the maximum flow of water and condensate
and should be able to tolerate 100 °C. [1]
Validation
Validation is described as a documented
procedure for obtaining, recording and
interpreting data required to show that a
process
will
consistently
comply with
predetermined specifications. [3]
In the case of autoclaves the validation process
may be broken down into the following tests:
Commissioning
Installation Checks
Installation Tests
Commissioning Tests
Performance Qualification
Thermometric Tests
Microbiological Tests
[1]
According to EN554:1994 “Sterilization of
medical devices – Validation and routine
control of sterilization by moist heat” [3], the
Commissioning tests need only be performed
at initial installation and after certain repairs
while the Performance Qualification tests
should be performed regularly and routinely.
Commissioning
“Commissioning: Obtaining and documenting
evidence that equipment has been provided
and installed in accordance with its
specification and that it functions within predetermined limits when operated in accordance
with operational instructions” [3]
Commissioning tests should include checking:
that the electrical supply is suitable for
the autoclave
that the temperature and humidity are
sufficiently well controlled
that there is no interference to or from
other equipment
the accuracy of indicators has been
certified to national standards
the temperature and pressure of the
chamber during a sterilization cycle are
within specifications
the leakage into the chamber during a
vacuum cycle does not exceed the
specified maximum
that there is no leakage of steam, water
or effluent at any point during the
sterilization cycle
that both water quality and steam
quality comply with the sterilizer
specification
the chamber is capable of withstanding
its specified maximum pressure. This
test may be a legal requirement and
should be performed by a suitably
certified organisation.
Performance Qualification
The performance qualification (PQ) tests
actually check that the autoclave is not only
functioning correctly, but also that sterilization
is taking place. Analysis of documented PQ
results can also assist with pro-active
maintenance schedules.
A thermometric test to determine the
temperature profile inside the chamber
throughout the holding time, using a data
logging system and multiple probes placed
throughout
the
chamber
volume.
Simultaneous monitoring of the chamber
pressure is also useful in checking the
efficiency of the air removal/replacement
system.
Once qualification of the empty chamber has
been accepted, load testing should be
performed. Here, similar probes as used in
monitoring the temperature profile, are placed
inside typical loads and the heat transfer time is
determined during the sterilization cycle.
These tests should be repeated for each type
of load and/or preprogrammed cycle that for
which it is intended to use the autoclave.
During the load testing, biological indicators
may also be placed in the load to determine if
sterilization is in fact taking place.
If the autoclave is to be used to sterilize folded
cloth, such as garments, a Bowie Dick test
should be performed to ensure complete
penetration of the steam into the cloth.
Maintenance intervals
The
intervals
between
Performance
Qualification tests should be determined based
on documented experience and the need, type
and previous performance of the autoclave.
EA-4/10 “Accreditation in Microbiological
Laboratories”
suggests
that
the
load
characteristic for each cycle be determined
every two years, while the chamber
temperature and time must be monitored during
each use. [2]
Regular maintenance such as gasket
inspection, and cleaning of the chamber should
be
performed
at
the
manufacturers
recommended intervals. A full service should
be performed at least annually as should the
safety check of the pressure vessel.
Any repairs or modifications of the unit may
require complete, or at least partial, recommissioning of the autoclave, including full
Performance Qualification tests.
performance qualification tests should be fully
recorded, reviewed, accepted and archived by
the relevant personnel in the organisation that
uses the autoclave.
These results may be recorded on suitable
worksheets and certificates may be issued by
third-party organisations that perform such
tests.
Routine Checking
Conclusion
Routine checking may be broken down into
daily, weekly, quarterly and annual checks.
The
commissioning
and
performance
qualification of an autoclave and subsequent
validation of the sterilizing protocols is a costly
and time consuming process, both in the actual
procedures involved and also in the analysis
and review of the resulting documentation.
Daily checks should be performed by the
operator and should include the observation of
all indicators for “normal” values.
On a weekly basis safety checks should be
performed such as inspection for leaks and
electrical wiring faults, inspection of door seals,
correct of operation of door interlocks and high
temperature and low water alarms. In the case
of vacuum autoclaves, a vacuum leak test
should also be performed.
Quarterly checks may include verification of the
calibration of the instrumentation, a check of
the automatic control functions, a check of the
vacuum leak sensor and a thermometric test on
a small load.
Annually, a full re-commissioning may be
warranted. Thermometric testing should be
performed. Load testing should be performed
as well, but different loads may be scheduled
into bi- or tri-annual cycles. [1]
Ensuring that sterilization is occurring in the
autoclave is however of prime importance
(otherwise why bother to autoclave in the first
place) thus such costs should be viewed in the
light of human safety rather than that of
economics.
At the same time, however, to ensure that
qualification and validation are performed
correctly, the tests should only be carried out
by suitably qualified and experienced personnel
and organisations.
References
[1]
A. Chandler, Introduction to Sterilization
[2]
European co-operation for Accreditation
EA-04/10 Accreditation for Microbiological
Laboratories, July 2002 rev02
European Committee for Standardization
EN 554:1994 Sterilization of medical
devices – Validation and routine control of
sterilization by moist heat, June 1994
[3]
Documentation
The results of all commissioning tests and