A steam sterilizer fails the Bowie-Dick test when air is not removed from the chamber before steam enters, when the steam itself is wet, or when the test pack is used incorrectly. The test is a deliberate check of air removal and steam penetration on a pre-vacuum sterilizer, run on an empty chamber at the start of the day. A failed sheet is not a failed sterilizer by default: placement, pack condition and indicator storage account for a large share of failures.
The test uses a Class 2 chemical indicator sheet inside a standardized test pack. It is not the same as the indicator tape on a pouch, and it is not a biological indicator. A Class 1 autoclave indicator tape tells you a pack was exposed to a process; it cannot tell you whether air was removed.
What does the Bowie-Dick test actually measure?
It measures whether the vacuum stage removed air from the chamber and whether steam then penetrated the test pack evenly. The indicator sheet changes colour uniformly when steam reaches every part of the pack; a patchy or central-only change means air remained trapped. Because air removal is the variable, the test must run on an empty chamber with a warm unit, using the cycle the manufacturer specifies.
On small Class B dental sterilizers, a related check is the helix test, which uses a process challenge device representing a hollow instrument. It answers a similar question for hollow loads: can steam reach the inside of a narrow lumen? Both tests belong to the same family of daily checks, and both are separate from the biological indicator.
What causes a patchy or failed Bowie-Dick result?
| Cause | What the sheet shows | First check |
|---|---|---|
| Insufficient vacuum depth | Central area unchanged, edges change | Vacuum pump performance and door seal |
| Air leak into the chamber | Repeatable patchy pattern in the same place | Door gasket, drain valve, fittings |
| Wet steam | Blotchy change with damp pack | Steam quality, water source, line insulation |
| Test pack used cold or incorrectly assembled | Uneven change that resolves on a second run | Pack assembly and warm-up cycle |
| Expired or badly stored indicator sheet | Little or no change across the sheet | Lot date and storage conditions |
| Overloaded chamber | Variable results between runs | Remove all items; the test is for an empty chamber |
How should the test be run?
Warm the unit with a cycle first, then run the Bowie-Dick cycle with the chamber empty and the test pack placed on the lower shelf, flat, away from the walls and door. Read the sheet after the cycle against the manufacturer's reference, and record the result with the date, cycle number and operator. Do not stack the pack against other items, and do not run the test in a load.
A failure is a stop signal for the day's wrapped loads on a pre-vacuum unit. Repeat once with a fresh pack to rule out a handling error. If it fails again, take the unit out of service for wrapped loads and call service; a unit that cannot remove air cannot sterilize a wrapped pack, even if the temperature and pressure readings look normal.
How does the Bowie-Dick test relate to the biological indicator?
They answer different questions and you need both. The Bowie-Dick test answers “did air removal work?” and runs daily on pre-vacuum units. The biological indicator answers “was the load actually sterilized?” and, in Ontario dental practice, is expected for each sterilizer on every day it is used. A unit can pass one and fail the other: a sterilizer with poor air removal will usually fail both, but a unit with a load-specific problem can pass the Bowie-Dick and fail the biological indicator from that load.
Keep the two records together. When a biological indicator turns positive, the Bowie-Dick result from the same morning tells you whether to look at air removal first or at the load and the indicator. That is the practical value of running both.
What should be recorded?
Record the date, time, sterilizer identifier, cycle type, test pack lot and result. Add the corrective action if the sheet failed, and the result of the repeat test. A binder that shows a consistent daily record with one documented failure and its repair is a stronger audit file than a perfect record with no deviations, because it shows the process can detect a problem.
Related reading
- ISO 11140-3 Class 2 chemical indicators for Bowie-Dick tests
- Small steam sterilizer classes N, S and B for dental clinics
- Why does autoclave tape stay pale tan after a cycle?
Download the printable sterilization log, or build one with the log generator. Ask a Compliance Specialist at our consultation desk. Ordering for a clinic, lab or care home? Wholesale and multi-site ordering covers account setup for institutional buyers. Start with a five-strip biological indicator sample request to pair the daily checks in one record. Reselling? become a distributor.
Frequently Asked Questions
Why did my Bowie-Dick test fail this morning?
Check air removal first: vacuum depth, door seal and drain valve. Then rule out a cold pack, an expired sheet or an overloaded chamber. A repeat failure means the unit should be taken out of service for wrapped loads.
Can I run a Bowie-Dick test with instruments in the chamber?
No. The test is designed for an empty, warm chamber. Items in the chamber change steam distribution and make the result uninterpretable.
Is autoclave tape a Bowie-Dick test?
No. Tape is a Class 1 process indicator. It shows exposure to a cycle, not that air was removed from the chamber.
Do Class B dental sterilizers need a Bowie-Dick test?
Follow the manufacturer's instructions and your provincial framework. Many Class B units use a helix test for hollow loads instead of, or alongside, a Bowie-Dick test, and the biological indicator requirement still applies.
CliniEco Medical is a licensed medical device establishment (MDEL #35334).
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