1What is a Bowie-Dick test?
The Bowie-Dick test, named after the two Scottish microbiologists who described it in 1963, is a Type 2 chemical indicator test defined in ISO 11140-1 and specified in EN 285 / ISO 17665. It does not test sterility. It tests whether a pre-vacuum sterilizer removes air from the chamber effectively and whether the steam that replaces it penetrates a porous load quickly and uniformly.
2Why air removal matters
Steam sterilizes by condensing on surfaces and transferring latent heat. Air trapped inside a pack forms a pocket that steam cannot enter, so the contents inside that pocket never reach sterilizing conditions. Pre-vacuum sterilizers pull a series of vacuums to remove air; a leaking door seal, a faulty vacuum pump or non-condensable gases in the steam supply all leave residual air behind. The Bowie-Dick test is designed to reveal exactly that.
3How to run the test
- Warm the sterilizer with an empty cycle at the start of the day.
- Place a standard Bowie-Dick test pack (or a disposable test pack that conforms to ISO 11140-4) horizontally on the lowest shelf, above the drain, in an otherwise empty chamber.
- Run the dedicated Bowie-Dick cycle: 134 °C for 3.5 minutes (never longer, or a weak fault may be masked).
- Remove the pack and examine the indicator sheet immediately.
4Interpreting the result
| Appearance | Interpretation | Action |
|---|---|---|
| Uniform colour change across the whole sheet | Pass — air removal and steam penetration are adequate | Record and release sterilizer for use |
| Lighter or unchanged area in the centre | Fail — residual air or non-condensable gases | Take the sterilizer out of service; call for maintenance; repeat test after repair |
| Uneven, patchy change | Suspect — possible wet steam or superheating | Investigate steam quality; repeat test |
5Documentation
File each test sheet, or a copy, with the date, sterilizer number, cycle number and operator. Most accreditation schemes require the Bowie-Dick record to be retained with the sterilizer log.
6Conclusion
The Bowie-Dick test takes ten minutes each morning and catches the single most common cause of steam sterilization failure — trapped air. Combined with a Type 1 tape on every pack, a Type 4/5 indicator inside every pack and routine biological monitoring, it forms the backbone of a compliant monitoring programme.
7Frequently asked questions
Does a gravity-displacement sterilizer need a Bowie-Dick test?
No. The test is specific to sterilizers with active air removal (pre-vacuum). Gravity sterilizers are monitored with chemical and biological indicators only.
Can I run the Bowie-Dick test with a load in the chamber?
No. The chamber must be empty apart from the test pack, so that the test reflects the sterilizer's own performance.
