Bowie-Dick test: how to run it, read it and record it
Step-by-step guide to the daily Bowie-Dick air-removal test for pre-vacuum sterilizers: cycle, placement, pass and fail patterns, and what to do on a fail.
In short: run a Bowie-Dick test every day the sterilizer is used, in an empty chamber, after a warm-up cycle and before the first load. A uniform colour change across the whole indicator sheet is a pass. Any lighter area — usually in the centre — is a fail, and the sterilizer should not process loads until the cause is fixed and the test passes.
What the test proves
A pre-vacuum steam sterilizer removes air from the chamber and the load before steam is admitted. If air stays trapped, it shields surfaces from steam and the load may not be sterilized. The Bowie-Dick test, described by J. H. Bowie and J. Dick in 1963, checks exactly this: whether air was removed and steam penetrated rapidly and evenly into a dense porous pack. It is a Class 2 “specific test” indicator under ISO 11140-1.
It does not check sterilization of a load. It checks that the machine is capable of removing air on that day.
How to run it
- Warm the sterilizer. Run one empty cycle first; a cold chamber can give a false fail.
- Place the pack alone. Put one test pack on its own in the chamber, normally on the bottom shelf near the drain, unless the sterilizer manufacturer specifies otherwise.
- Select the Bowie-Dick cycle. The usual test cycle is 134 °C with a holding time of 3.5 minutes. Do not use a longer cycle — extra time can mask a marginal failure.
- Remove and read immediately. Open the pack and read the indicator sheet as soon as it has cooled enough to handle.
- Record the result. Write the date, sterilizer number, cycle number, operator and result on the sheet or in the log, and keep the sheet with the sterilizer records.
Reading the indicator sheet
| What you see | Result | Likely meaning |
|---|---|---|
| Even, complete colour change from edge to centre | Pass | Air removal and steam penetration were adequate. |
| Lighter patch or ring in the centre | Fail | Air was trapped: inadequate vacuum, a chamber leak or non-condensable gases in the steam supply. |
| Patchy or uneven change across the sheet | Fail | Wet or superheated steam, or an incorrectly placed pack. |
| No change at all | Fail | The cycle did not reach temperature, or the wrong cycle was selected. |
When the test fails
Take the sterilizer out of use for loads, repeat the test once to rule out a handling error, and if it fails again call the engineer. Common causes are a leaking door seal, a failing vacuum pump, a faulty air-detection system, or steam quality problems. After repair, the machine should pass a Bowie-Dick test before it returns to service.
Ready-made packs versus towel packs
The original test used a stack of folded cotton towels with an indicator sheet in the middle (the standard test pack in ISO 11140-3 and EN 285). Most CSSDs now use single-use packs made to ISO 11140-4: they are lighter, consistent from pack to pack and do not depend on how towels have been laundered. The SteriCraft® Bowie-Dick test pack is one of these, with a blue-to-black change across the sheet.
Benchtop sterilizers
Small Class B sterilizers under EN 13060 also remove air by vacuum and should be tested daily. Use the air-removal test the sterilizer manufacturer specifies — a Bowie-Dick pack or a helix test for hollow instruments.