Air removal testing answers a question a biological indicator cannot: did the air actually leave the chamber? A pre-vacuum sterilizer can pass a spore test and still be trapping air pockets inside a load, because the surviving-spore test reads the load, not the chamber's atmosphere.
The Bowie-Dick test targets the empty-chamber behaviour itself. That is why it runs on a bare chamber, at the start of the day, before any instrument load goes in.
What does a Bowie-Dick test actually verify?
It verifies steam penetration and air removal: uniform, rapid steam contact across the pack during the exposure phase. The test pack is designed so that a residual air pocket leaves a cold spot, and the indicator sheet inside shows it as an incomplete, uneven colour change.
Read the sheet as a pattern, not a colour. Uniform change across the whole sheet is a pass. A pale centre, a crescent or a blotchy edge is a fail, and the pass or fail decision belongs to the pattern on the sheet — not to how the cycle looked on the panel.
How often is air removal testing required?
For pre-vacuum (Class B and equivalent) units, the operating expectation in most North American sterile processing guidance is a Bowie-Dick test at the start of each day the sterilizer is used, on an empty chamber after warm-up. Classic gravity displacement units are handled differently and do not take a Bowie-Dick pack at all, because the mechanism being tested is not present.
Two administrative habits keep this defensible. Run the test before the first load rather than between loads, and record the result on the same daily sheet as the biological indicator, so the two monitoring lines read together.
| Test | What it verifies | Chamber state | Typical cadence |
|---|---|---|---|
| Bowie-Dick (Type 2) | Air removal and steam penetration | Empty, after warm-up | Each day the unit is used |
| Biological indicator | Sterility assurance at the load level | A real production load | Per the clinic's SOP, driven by usage |
| Class 4 / 5 / 6 indicator | Exposure conditions inside the pack | Every pack | Every load, every pack |
| Mechanical record | Time, temperature, pressure curve | Every cycle | Every cycle, printed or logged |
What is the difference between Class 4 and Class 6 steam sterilization indicators?
Both are chemical indicators, and neither replaces a spore test. Class 4 is a multi-variable indicator that responds to two or more critical variables and is intended for use inside packs. Class 6 is an emulating indicator calibrated to the sterilization cycle parameters it is designed to monitor, which is why a Class 6 strip is cycle-specific in a way a Class 4 pouch marking is not.
In practice, clinics often use both: a Class 4 dual-indicator pouch as the packaging and pack-level check, and a Class 6 strip in high-risk or implant-related loads where a cycle-specific emulating indicator is required by the facility's policy.
What do you do when a Bowie-Dick test fails?
Stop. Do not run patient loads until the test passes. Repeat the test once on a properly warmed chamber with a new pack — a single failure after an overnight shutdown is sometimes a warm-up problem rather than a mechanical one.
A repeat failure means the air-removal system needs service: typically a vacuum pump, valve, door gasket or drain issue. Document the failure, the repeat, the service call and the first passing test after service, and record which loads were reprocessed.
Dental steri pouch for sterilizer — plastic up or paper up?
For self-sealing sterilization pouches, load them with the transparent film facing the same direction across the tray where the manufacturer's instructions allow, and keep the paper side free of direct contact with the chamber shelf. Orientation matters less than three other things: no overloading, packs standing on edge rather than stacked flat, and pouches sized so the seal is not under tension.
Not sure which monitoring consumable fits your cycles? Start with the BI 5-pack trial (CA $12.99, shipping included), or request a quote for volume pricing.
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.
Related reading
Why autoclave cycles fail the Bowie-Dick test; Bowie-Dick test packs compared; Class 4 vs Class 6 chemical indicators; sterilization compliance hub.
Frequently Asked Questions
Can a Bowie-Dick test replace a biological indicator?
No. The Bowie-Dick test checks air removal and steam penetration in an empty chamber; a biological indicator checks whether spores survived in a real load. A complete monitoring program records chemical, biological, mechanical and air-removal evidence separately.
Does a gravity displacement autoclave need a Bowie-Dick test?
Generally no, because there is no pre-vacuum air removal stage for the test to measure. Gravity units are monitored with chemical indicators, a biological indicator cadence set by the facility, and the mechanical record of each cycle.
What should a Bowie-Dick test pack contain?
A disposable pack holds a porous stack and an indicator sheet positioned in the centre of the pack, so a residual air pocket shows up at the point least likely to be reached by steam. Reusable packs must be reassembled exactly as the manufacturer specifies or the reading is invalid.
Last updated: September 2025. CliniEco Medical is a licensed medical device establishment (MDEL #35334).
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