Quick answer: A four-chair dental office in Hamilton ran a Bowie-Dick test on a pre-vacuum sterilizer and got a dark, uneven sheet. The office stopped the sterilizer and re-processed two loads. The cause turned out to be an air leak at a door gasket, not a pump failure. The case shows why the test must be run on a warmed, empty chamber and why an uneven sheet is treated as a fail rather than as a borderline result.
What is a Bowie-Dick test actually checking?
The Bowie-Dick test checks air removal, not sterilization. It is run only on pre-vacuum sterilizers, because those machines remove air with a vacuum pump before steam enters. If the pump, valves or door seal leak, air remains trapped and steam cannot reach the centre of dense loads reliably.
The test uses an indicator sheet inside a standard test pack. A uniform colour change across the sheet means air was removed evenly. A dark centre, a pale centre or an uneven pattern means air removal failed, and the result is a fail, not a partial pass.
When and how should the test be run?
Run it before the first load of the day, after the chamber has warmed up, in an otherwise empty chamber. A cold chamber can give a misleading result because trapped air behaves differently before the unit reaches operating temperature. The pack goes in the same position each time, generally low and toward the front of the chamber where the manufacturer specifies.
Record the sheet or its photograph with the date and sterilizer identifier. Because the result is visual, the record is the only evidence available six months later, and a written pass with no image is a weak record.
| Result pattern | Meaning | Action |
|---|---|---|
| Uniform colour change | Air removal adequate | Release the machine for the day |
| Dark or pale centre | Air trapped in the pack | Stop, quarantine loads, repeat the test |
| Uneven or patchy sheet | Inconsistent steam contact | Stop, quarantine loads, call service |
| Repeat fails the same way | Mechanical fault, e.g. door gasket | Repair, then re-test and run a biological indicator |
What did the office do when the sheet failed?
They stopped the sterilizer immediately, quarantined the loads from that morning and re-processed them in a second unit. They then repeated the test with a new pack to confirm the result was reproducible rather than a single bad sheet.
The repeat failed in the same pattern. A service call found a worn door gasket allowing a slow leak. After replacement the test passed, and the office ran a biological indicator before returning the unit to routine use. The whole event cost about half a day, which is what a correct reaction looks like.
How does this differ from biological monitoring?
Chemical and Bowie-Dick style tests check process conditions: air removal, temperature and steam contact. A biological indicator checks whether the cycle actually killed a resistant spore population, which is the only direct evidence of sterility assurance. They answer different questions, which is why a clinic cannot drop one because it runs the other.
In Ontario, the expectation is a biological indicator for each sterilizer on every day it is used. The Bowie-Dick test sits alongside that as a daily check on pre-vacuum machines, not as a replacement for it.
What should go into the clinic policy after a failure like this?
Write the reaction into the policy, not the emotion. A failed test means the sterilizer stops, affected loads are quarantined, the test is repeated to confirm, service is called, and a biological indicator must pass before routine use resumes. Put the sequence on a card at the machine so the response does not depend on who is on shift.
Also record the service visit and the gasket replacement in the same log. That record turns a stressful morning into a documented maintenance history, which is exactly what a reviewer wants to see.
Related reading
Bowie-Dick test packs; biological indicator 5-pack trial; where to buy Bowie-Dick test packs in Ontario; the annual cost of Bowie-Dick testing.
Download the printable autoclave log and spore test templates, run the sterilization self-check with your team, and ask a compliance specialist before an inspection.
Ordering for a clinic, lab or care home? Wholesale and multi-site ordering covers case pricing and account setup, and the B2B wholesale collection lists the lines stocked for institutional buyers. Reselling? become a distributor.
Frequently Asked Questions
Is a Bowie-Dick test a sterility test?
No. It checks air removal in a pre-vacuum sterilizer. Sterility assurance comes from biological monitoring, which is why the two tests sit alongside each other rather than replacing one another.
Should a Bowie-Dick test be run in a cold chamber?
No. Run it after the chamber has warmed up, in an otherwise empty chamber, in the same position each time, because a cold chamber can give a misleading result.
What does an uneven Bowie-Dick sheet mean?
It is a fail. An uneven or dark-centred pattern means air removal failed, so the sterilizer stops, affected loads are quarantined and a service call follows.
What must pass before the sterilizer returns to use?
The Bowie-Dick test must pass again and a biological indicator must pass, with the service visit recorded in the same log as the routine monitoring entries.
CliniEco Medical is a licensed medical device establishment (MDEL #35334).
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