Steam penetration test
A steam penetration test is used to control the sterilization process of a class B steam sterilizer (fractionated pre-vacuum process). The official designation of the steam penetration test is: steam penetration test for hollow bodies ; engl. hollow load process challenge device or hollow load challenge test . The test body simulates loads of the classification hollow body A for small steam sterilizers of type B according to the standard DIN EN 13060 and is also a type test for large sterilizers according to DIN EN 285.
The test body (helix test body) used for the steam penetration test is the series connection of cavities of different lengths and volumes. This simulates the venting properties of typical medical instruments. There are different test bodies for the different specialist areas (surgery, ophthalmology, dentistry) in order to do justice to the different hollow instruments. According to DIN / EO / ISO 11140-1 (see below), the test body is a class 2 chemical indicator, which consists of a test body (PCD = Process Challenge Device ) and an indicator system (indicator strips).
The steam penetration test is used to check whether there is sufficient steam penetration at the end of a test body. The test specimens for the steam penetration test are called Process Challenge Device (PCD). Because of the currently widespread shape of the test body - a coiled hose - the steam penetration test is often referred to as the helix test. But there are also other types of test specimens that have the same properties. The tests available on the market differ considerably in their sensitivity.
Details are described in the following standards:
- Standard DIN 58921 (German version from January 2011) "Test method to demonstrate the suitability of a medical device simulator during steam sterilization - Medical device simulator." testing. ")
- Standard DIN EN ISO 11140-1 (German version EN ISO 11140-1: 2009 of September 2009): “Sterilization of health care products - Chemical indicators - General requirements.” (English: “Sterilization of health care products - Chemical indicators - Part 1: General requirements. ")
- DIN EN ISO 11140-3 (German version EN ISO 11140-3: 2009): "Sterilization of health care products - Chemical indicators - Class 2 indicator systems for use in the Bowie-Dick steam penetration test."
- DIN EN ISO 11140-4 (German version EN ISO 11140-4: 2007): "Sterilization of products for health care - Chemical indicators - Class 2 indicators, which are used as an alternative to the Bowie-Dick test for the detection of steam penetration. "
- DIN EN 867-5 (Helix "Hollow A") - was adopted as
- DIN EN ISO 11140-6: this is where the actual description of the specification for the helix test takes place.
Further standards for these test bodies are:
- DIN EN 867-5 (from November 2011), in which test specimens with 1.5 m PTFE hose length and PTFE capsule are described: “Non-biological systems for use in sterilizers - Specification of indicator systems and test specimens for testing the performance of small sterilizers of type B and type S. ”as well as the ISO standard with the same title
- ISO 11140-5 (of March 2007): "Non-biological systems for use in sterilizers - Specification of indicator systems for testing the performance of small sterilizers of type B and type S."
A Process Challenge Device (PCD) consists of a test body and detector, which usually consists of a chemical indicator and is a test device with which the penetration capacity of the sterilizing gas (e.g. steam) ( sterilization ) is assessed.
A PCD can be used to verify steam, ethylene oxide, formaldehyde, and hydrogen peroxide sterilization processes. The PCD was formerly known as a challenge (English challenge for to question, to doubt), test pack or challenge test pack .
There are, among others, the following process challenge devices for sterilizers:
- Bioindicator PCD (spore test)
- Helix test PCD (a steam penetration test for hollow bodies; English: hollow PCD or tubular test device ) - test bodies for testing the performance of small and large steam sterilizers
- Bowie-Dick-PCD ( Bowie-Dick-Test ) - for use in the daily Bowie-Dick-Steam Penetration Test which consists of a porous PCD
The result of a sterilization cannot be checked on the end product, since a "non-destructive" direct check of the sterility is not possible. Since direct testing of the sterile items is impossible without loss of sterility, a number of indirect controls are used. Just measuring pressure and temperature in the sterilizer is not enough. A hard-to-reach point is constructed in the PCD at which non-condensable gases can accumulate in sufficient quantities to be able to make a reliable statement about the penetration of the sterilizing gas (steam, ethylene, formaldehyde, hydrogen peroxide).
A problem with sterilization has proven that the sterilizing gas does not always reach all outer and especially inner surfaces of the items to be sterilized ("item to be sterilized" is the unsterile and unfinished "product"; "item to sterile" is the fully sterilized "product") ). If the air is not removed from the hollow bodies of the items to be sterilized, then no sterilizing gas can penetrate and sterilize them. Therefore, for example, hollow body tests can be carried out for the removal of the air and the penetration of the steam (steam penetration). In order to reach all inner surfaces, the air must be removed from the steam sterilizer - and thus from the items to be sterilized - by means of a vacuum before the actual sterilization process. During the sterilization, no non-condensable gases (NCGs) may be present or accumulate in the hollow-bodied instruments to be sterilized. Residual air that has not been removed from the sterilizer chamber accumulates here. In practice, it is precisely these complex hollow instruments that are difficult to vent and sterilize. The helix test is used in steam sterilization processes to check a specific steam penetration performance.
The requirements for the test body for the helix test or, more generally, for a test system for a B-class autoclave are described in EN 867/5 Steam . The helix test is the standard test for B-class small sterilizers according to EN 13060. The helix test is a specific indicator and can be a batch monitoring system (BMS). A batch monitoring system for steam sterilization processes based on DIN 58921 is used to validate a sterilization process for a specific sterilization batch and it is achieved using test specimens and inserted indicator strips (helix test).
An autoclave of the B-class must be checked for functionality every working day, meaningfully during the first sterilization in the morning, using a helix test. Furthermore, all sterilization batches with instruments of hazard class critical B must be checked with a batch control (e.g. a helix test).
In contrast to the older autoclaves of classes N and S, an autoclave (steam sterilizer) of class B works with a pre-vacuum that is built up several times (usually 3–4 times) before the actual sterilization process ("fractional pre-vacuum"). The fractional pre-vacuum ensures that hollow bodies with complex geometry can also be safely sterilized, as well as instruments packed in sterile barrier systems (medical packaging).
The helix test is used to monitor this fore-vacuum.
The hot steam can only reach the detector (chemical indicator) when the test system has been successfully evacuated by the fore-vacuum. The helix test is used to check the functionality of the vacuum system of the B-class autoclave, leaks and NKG in the steam. The helix test does not replace the spore test (bio-indicator) if no chemical indicator at least equivalent to class 5 or 6 according to DIN EN ISO 11140-1 is used as the detector. Commercially available bioindicators can also be used as a detector in a helix test. If sterilization processes with hollow-body instruments have to be validated, the helix test is a simple and inexpensive method to prove sufficient penetration of the steam into the hollow body, provided that the PCD is more difficult to ventilate than the hollow body to be sterilized. However, the helix test only covers this part of the validation. The coiled hose (from helix "snail") gave this test its name.
The helix test is more relevant in practice for small sterilizers than the Bowie-Dick test . The helix test checks the steam penetration of hollow bodies ( e.g. contra-angle handpieces ; packaged instruments), which is relevant for the dental sector .
The Bowie-Dick test, originally a steam penetration test for a 7 kg textile package, is unsuitable for small sterilizers because it exceeds the maximum permissible load for a small steam sterilizer, which is usually 5 kg. There are, however, much smaller and lighter alternatives that serve the same purpose. However, porous goods have other, usually simpler, steam penetration properties than hollow bodies.
The results of the helix test must be documented. However, the indicator strips with the color change do not have to be kept. Helix tests are offered under different names with different tube lengths and diameters.
The detector of the Helixtest usually consists of a chemical indicator that changes color to indicate when it has come into contact with hot water vapor. The indicator strip is located in a screwed test body into which the steam cannot enter directly, but only via a 1.5 m long and 2 mm internal diameter thin Teflon hose. Hollow bodies closed on one side are comparable to hollow bodies of double length, which are open on both sides and otherwise identical in terms of geometry and material. Since the hose of the helix test could become porous and leaky after repeated use, the maximum number of permissible test cycles per test body is specified by the manufacturer. Instead, PCD devices made of stainless steel are also offered, which have a very long shelf life.
literature
- J. Gömann, U. Kaiser: Investigations into the ventilation of hollow bodies in steam sterilization processes. Zentr Steril (6) 1998: 401-403