Dear Sir,
Can Bowie and Dick Test use for Gravity Displacement Sterilizer? In my opinion, I think that Bowie and Dick Test can use or apply to Gravity Displacement Sterilizer.
Your Faithfully
Charay Patthanathongdee

Hi Charay,
the Bowie-Dick Test is not a sterilization test, it is a test of the effectivness of the vacuum system of the sterilizer. It is not performed on gravity-displacement sterilizers (because these sterilizers do not have a vacuum system, and it is not a substitute for biological monitoring or for routine chemical monitoring of packaged items.
Greetings Josy

Dear Charay,
I want to give a complementary remark.
EN285: "Sterilization - Steam sterilizers - Large sterilizers" says in clause 19:
The Bowie and Dick test was conceived as a test for successful air removal for sterilizers so called high vacuum porous load sterilizers. A successful Bowie and Dick test indicates rapid and even penetration of steam into the test pack.
etc....
Kind regards
Wim Renders

Hi everybody,

Let me share some idea on this issue. In Thailand now most of hospitals are using the gravity displacement steam sterilizers. As we know that the gravity displacement is using steam itself to remove air out of the chamber via steam trap actually. But in reality not so many people take good care and keep well maintain of this steam trap. As a result steam trap is not working properly then cause air remained in the chamber and poor the sterilization process occured eventaully. I have tested by putting Bowie and Dick test into the sterilizers which have steam trap problem and found that the test was fail but after cleaning the steam trap and it became working well, the Bowie&Dick test shown uniform black. I am awared that the Bowie&Dick has been designed to check a steam penetration in prevacuum sterilizer but it seems working in the same principle in gravity displacement. If it can not be used, what should be a reason and what test should be done in testing a successful air removal from the porous load in gravity displacement???

Chaisynn Sirisongtham

hi all

the real way to monitor air removal from a gravity machine is to compare the temperature measured in the drain with the corresponding steam-table temperature from the chamber pressure. This is not always accurate but the machine should control the chamber conditions by pressure and monitor the achievement of sterilizing conditions by temperature. The control steeings should be set to accurately reflect the air-removal. A Bowie and Dick test pack is not designed for this process in a garavity machine.

best wishes, peter hooper, UK

You surely think why then does my BD-Sheet change the color to uniform black!
Because in downward displacement sterilizers the indicator is likely to change color completely while air is still present in the pack. The same goes for use in the steam-flush pressure-pulse sterilizers.
The only standard for Downward displacement Sterilizers for In-Hospital use I know of, are the Australian Standards:
AS 2192 1991 Sterilizer-Steam-Downward displacement.
published by the Standards Association of Australia, 1 The Crescent, Homebush, NSW 2140
or get in Contact with Philip Robins, Sterile Supply Service Advisor, Technical Service, Health Dep. of Western Australia, 189 Royal Street, East Perth W.A. 6004, FAX: 09 2224077
or visit the Australian Websites for Sterilization; see links on our EFHSS-Site.
Greetings from Josy Holdener

Dear Peter Hooper,

Thank you for your valuable comment. You talked about steam-table between temperature and pressure. It will be a very good reference document to us but where I should find it. If you have had on hand, please e-mail to my e-mail address:

Many thanks

Chaisynn

Dear Chary,

Can the Bowie & Dick test be used in gravity displacement sterilisers? Yes, it can.
Why? Because there are no reasons why it shouldn't!
The Bowie & Dick test is a steam penetration test for porous loads (textile packs). Although it was originally designed to be used in high vac sterilisers, it is used now in fractional vacuum sterilisers, which are quit different from high vac sterilisers. If you do the Bowie & Dick test in your steriliser and it passes the test it gives you an indication that the steriliser is suitable for the sterilisation of textile packs. One thing is very important with every test you do with chemical indicators; you must ensure that the indicator is not exposed to the sterilisation conditions for too long or that the sterilisation temperature is too high. For example, if the indicator is designed to change colour in saturated steam of 134°C in 3 minutes, you make sure that the exposure of the indicator to steam of at least 134°C is not longer than 3 minutes and that the temperature is not much higher than 134°C (see EN867-3 for the allowed tolerances). Very often the indicator of the Bowie & Dick test is over exposed and small penetration faults are disguised. This is unfortunately also very true for vacuum sterilisers. The sterilisation conditions (time and temperature) in the test pack must be verified by measurement.
We, at the National Institute for Public Health in the Netherlands, did some research on gravity displacement sterilisers as they are in use in the third world countries; basically large pressure cookers. We found that these sterilisers with the correct procedure are well capable of sterilising textile packs and give a good performance of the Bowie & Dick test and fulfil the requirements for load dryness in EN285. Without the use of a vacuum pump. The report can be downloaded from the RIVM website:
http://www.rivm.nl/bibliotheek/rapporten/318902011.html

From the reactions on your question I am confirmed in my earlier impressions that there is a lot of confusion about the Bowie & Dick test. For the revision of EN285 I wrote a proposal for an informative annex to EN285, explaining the position of the Bowie & Dick test in the totality of performance tests for steam sterilisers. Please accept it as my personal view on the matter.

"Informative annex on the tests using the standard test pack. The small load thermometric is used as the basic test for large steam sterilisers. It is typically performed during process development and subsequent type testing as well as during the operational qualification. The materials and dimensions of the test pack are chosen to be identical to the 'standard' Bowie and Dick test (see clause 19), which has been in use for decades as a routine sterilizer test in many countries throughout Europe. The factors influencing the penetration of steam into this test pack have been the subject of many investigations over the years. Literature on the subject is abundantly available.

Readers of this standard are however warned against overrating of the value of any tests in which the standard test pack is used.
* The standard test pack bears no intentional relationship to the loads that are routinely sterilised in the particular steriliser. Nevertheless it is obvious that, because the test pack is composed of steam permeable, water absorbent porous material, it is closer related to porous loads (linen, drapes, gauze, bandages etc.) than to solid or hollow stainless steel surgical instruments. The value of the tests in which the standard test pack is used for steam sterilisers that are not intended to be used with porous loads (typical instrument steriliser) is therefore limited.
* The standard test pack does not present a particular great challenge to the air removal system. Against common believe vacuum assisted air removal is not necessary to obtain satisfactory steam penetration in the standard test pack (and full porous loads for that matter) [B. Muis et al, RIVM 318902011].
* The standard test pack is not necessarily the worst case load. The materials and dimension of the test pack are not chosen on the basis that this will present the worst case load for any particular steam steriliser. The materials and dimensions of the testpack are not chosen on scientific grounds, but merely on the historical availability of these materials in hospitals. Data are available to show that in small steriliser chambers (1 to 4 stu) a smaller test pack may actual present a greater challenge to the process than the standard test pack [Meurer et al, Central Service Vol. 8, 2000].
In small chambers (from 1 stu to 4 stu) the steam penetration is influenced by the position of the steam inlet and drain relative to the test pack. Depending on the actual configuration steam might be partially injected into the test pack. Other influences that are of relative great importance in smaller steriliser chambers are the velocity of steam entering the steriliser chamber, the velocity and quantity of fluids being drained from the steriliser chamber and rate of pressure change [reference Hurrell, Kingston?]. Whereas these factors may give a positive contribution to the steam penetration in the test pack, this is not necessarily the case with routine steriliser loads.
Studies have been performed in which the steam penetration into the standard test pack and steam penetration into hollow devices is compared, to show that hollow devices may present a far greater challenge than the standard test pack [Gömann et al. Central Service Vol 3, 2001].

A steam steriliser capable of a successful thermometric small load test is not a 'good for all steriliser'. Such a steriliser is not necessarily capable of sterilising porous materials of different composition (mixed cotton-polyester/ micro-fibres/ laminated fibres), larger or smaller pack sizes, packs wrapped in materials conforming to EN868-2/sub., stainless steel surgical instruments, hollow devices or lumen. The capability of the particular steam steriliser to sterilise the actual loads (specific medical devices, packaging, loading configurations, amounts, etc) when connected to the facilities that are available in the given situation shall be established by performance qualification to international standard (ISO 17665)."

Adrie de Bruijn
National Institute of Public Health and the Environment (RIVM)
PO Box 1
3720 BA Bilthoven
The Netherlands

The B-D test was originally designed to document air removal for preconditioning phases consisting of vacuum only (could have series of negative/positive pulses while still under vacuum). In the US, healthcare sterilizers have vacuum cycle with preconditioning phase consisting of a steam purge for a timed period, followed by a series of positive and negative pulses prior to the exposure phase. Since the preconditioning phase mixes steam and air and is efficient in air removal, does anyone know if the traditional B-D test is appropriate? I read some time ago in an old HTM-10 document that it wasn't.
Chip Moore
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Sterilization Products
Getinge/Castle
Rochester, NY
716 272 5123
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