A Bowie-Dick test fails when a vacuum sterilizer cannot remove air from the chamber quickly and completely enough. In plain terms, the pack is telling you that steam did not reach the centre of the load the way it should have. The usual suspects are an air leak, a vacuum pump that has lost its edge, or a test pack that arrived cold or damp.
For offices that run pre-vacuum or Class B sterilizers, the pack is a daily early-warning system. When it fails, pause, find the cause, and fix it before any instruments are processed.
Quick Facts
- The Bowie-Dick test is a Type 2 test device described in ISO 11140-4 and ISO 11140-5, used only on vacuum-assisted sterilizers.
- It detects air leaks and poor air removal, not the killing power of the cycle itself.
- Running it on the first vacuum cycle of the day is standard practice, consistent with CSA Z314.8 guidance for health care settings.
- A failed pack means the sterilizer should leave service until a qualified technician finds the fault.
What the Bowie-Dick test actually detects
Pre-vacuum sterilizers pull air out of the chamber before admitting steam, and the design works only if that vacuum phase is sound. A slow air leak, a tired pump, or a clogged drain can leave pockets of air that steam cannot penetrate. Instruments inside those pockets stay unsterile even when the chamber gauge reads normally.
A Bowie-Dick pack is a dense stack of paper sheets with a chemical indicator at its core. During a correct cycle the colour change is uniform; an uneven result, such as a lighter centre or streaking, means air stayed trapped.
Common causes of a failed test
Failures usually fall into a few patterns, listed below with where to look first.
| Symptom | Likely cause | First check |
|---|---|---|
| Patchy or streaked indicator | Air leak around the door seal or vacuum line | Door gasket and chamber seal |
| Centre of the sheet stays lighter | Air trapped in the pack core | Vacuum depth, pump performance |
| Sheet comes out damp or wrinkled | Wet steam or a cold chamber | Warm-up routine, steam trap, drain |
| Failures repeat on the same unit | Worn vacuum pump or sensor drift | Service inspection by a technician |
One failed test deserves attention; repeated failures demand a service visit, not another pack.
Why air, cold chambers, and mismatched packs fool the test
Air leaks
Door gaskets dry out and fittings loosen over time. A leak that barely moves the pressure gauge can still slow air removal enough to fail the pack, and many offices find the gasket is the culprit only during a technician leak test.
Cold chambers and wet steam
A chamber that has not finished warming up, or steam carrying too much moisture, can produce a damp pack with an uneven indicator. That is why manuals ask you to complete warm-up cycles before testing.
Pack size and chamber mismatch
Bowie-Dick packs are sized for specific chamber volumes, so a pack meant for a larger unit may not challenge a benchtop sterilizer properly. Use the size your sterilizer manufacturer lists for your model.
What to do after a failed Bowie-Dick test
Treat the result as real until proven otherwise. The sequence below keeps the practice safe and the records clean.
- Do not use any load processed since the last passing test; set it aside for reprocessing.
- Remove the sterilizer from service and contact a qualified technician.
- Log the failure with the date, cycle number, and pack lot.
- After repair, verify the unit, then rerun the test before processing instruments.
- Once the test passes, resume routine chemical and biological monitoring.
Building a routine that catches failures early
The Bowie-Dick test is one layer of a monitoring system. Autoclave indicator tape shows which packs were exposed, and Class 5 chemical integrators respond only when time, temperature, and saturated steam all come together. Biological indicators ask the direct question: were spores killed? In Ontario, the RCDSO requires a biological indicator for each sterilizer on every day that it is used — daily monitoring, not weekly. The weekly baseline is the CDC / AAMI ST79 standard in most US states. Our 24-hour rapid-readout biological indicators keep that answer within a day.
Keeping Bowie-Dick test packs on the shelf means the first cycle of the day never gets skipped.
Frequently Asked Questions
How often should we run the Bowie-Dick test?
For pre-vacuum and Class B sterilizers, standard practice is once a day on the first vacuum cycle before instruments are processed, in line with ISO 11140-4 and CSA Z314.8. Gravity-displacement sterilizers do not use a vacuum phase, so the test does not apply.
Can the test pack itself cause a failure?
Yes. A cold, damp, expired, or wrong-sized pack can mislead. Store packs flat at room temperature, check expiry dates, and use the size your sterilizer manufacturer specifies. If a fresh, properly handled pack fails, call for service.
What should we do with loads already processed?
Treat them as unsterile and reprocess them after the sterilizer passes a fresh Bowie-Dick test. Document the decision in the quality log so the event stays traceable.
A failed Bowie-Dick test is inconvenient, but it is the test doing its job: it caught a real problem before instruments reached a patient. A spare pack on hand and a clear response plan keep the disruption small.
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