You’ve probably been doing this test for years. If you’re not sure exactly what it proves, when it can give you a false answer, or what to do when the indicator looks “a bit off”, this is the article for you. Written for dental nurses and decontamination leads who run the test every morning and want to feel confident about it.
There are two tests that do essentially the same job, prove that your vacuum-cycle autoclave can remove air from a worst-case load. Which one your machine uses depends on the model. The principles are the same either way.
This is the bit that tells you whether you need to run the test at all. HTM 01-05 paragraph 4.16 is unambiguous:
“The daily tests should be performed by the operator or user and will normally consist of: a steam penetration test, Helix or Bowie-Dick tests (vacuum sterilizers only); an automatic control test (all benchtop sterilizers) in line with manufacturers’ instructions; a record of the temperature and pressure achieved at the daily test, to ensure this is satisfactory before the autoclave is used for sterilizing instruments.”
Three things to take from that.
Daily. Not weekly. The steam-penetration test runs every morning before clinical use. The weekly test you’re thinking of is the air-leakage test, which is a different test, same machine, different cycle, different purpose.
Vacuum sterilizers only. Type B and Type S machines. If you’ve got a Type N (non-vacuum, gravity-displacement) autoclave, it doesn’t have a steam-penetration test because it can’t process the load types that would need one. Type N machines have a residual-air test instead.
You’re the right person to do it. The “operator or user” wording means the dental nurse or another member of the practice team, not a service engineer. This is part of your morning routine, not a paid call-out.
A vacuum autoclave’s job is to use a series of pre-vacuum pulses to strip air out of the chamber and the load before the sterilising phase. If air gets left behind: in a pouch, in the hinge of a forceps, in the lumen of a handpiece, that air stops steam reaching the surface, and the surface doesn’t get sterilised even though the chamber thinks it has.
The Bowie-Dick and Helix tests are steam-penetration tests. They prove the vacuum stage is working properly by putting a worst-case challenge inside the chamber and checking whether steam gets all the way to the indicator.
Critically, they do not prove that today’s clinical loads are sterile. They prove the machine is capable. A passing test in the morning gives you confidence that the cycles run during the day stand a chance of being effective, provided the loads are cleaned, packaged, and loaded properly. The test itself is run on an empty chamber.
Both tests live under the same EN ISO 11140 standard family (Bowie-Dick simulators specifically under part 4, Helix devices under part 6), and both achieve the same thing. The difference is which worst-case load they simulate.
The Bowie-Dick test uses a porous-load challenge, a stack of cotton or a single-use simulator pack designed to mimic the air-removal challenge of wrapped, porous items. A chemical-indicator sheet sits in the middle of the pack. After the cycle, the sheet should show a uniform colour change right across, including the centre. Bowie-Dick is the traditional test, originally specified for the 7-kg cotton pack under EN 285.
The Helix test uses a hollow-load challenge. It’s a 1.5-metre PTFE tube, 2mm internal diameter, closed at one end with a small capsule that holds an indicator strip. Steam has to travel the full length of the tube, displacing the air ahead of it, before the indicator changes colour. The Helix is the newer test (BS EN 867-5, now EN ISO 11140-6) and is increasingly the standard choice for dental because it simulates the lumen of a handpiece or suction tubing better than a porous pack does.
Which one you run depends on your machine and what your supplier provided. Both are HTM 01-05 acceptable. Don’t switch between them without checking the manufacturer’s instructions, your autoclave will have a specific cycle for whichever test type it’s designed for.
The mistakes that lead to false failures almost all happen in the first three minutes of the routine. Worth doing this carefully.
Step 1: Pre-checks (HTM 01-05 paragraph 4.20). Wipe the door seal with a clean, damp non-linting cloth. Check the chamber and shelves are clean, no debris, no residue. Top the reservoir up with distilled or RO water (never tap water, minerals foul the chamber). Switch the machine on.
Step 2: Warm-up cycle. This is the single most common cause of a false failure. Most B-type autoclaves need a warm-up cycle before the steam-penetration test will run reliably. Running a Bowie-Dick into a cold chamber gives patchy, often-failing results even when the machine is healthy. Check your specific model’s manual: if it says warm up first, warm up first.
Step 3: Test pack placement. Empty chamber. No clinical instruments going through alongside the test. For a Bowie-Dick pack, position it on the lowest shelf near the chamber drain, that’s the most challenging position for air removal, which is the point. For a Helix device, sit it on the front of the bottom tray with the open end of the tube unobstructed.
Step 4: Cycle selection. Use the dedicated Bowie-Dick / Helix / Steam Penetration cycle on the machine’s menu. Not the routine 134°C instrument cycle. The test cycle has specific parameters (typically 134°C, 3.5-minute hold, multiple pre-vacuum pulses) and any other cycle will give a meaningless result.
Step 5: Read the indicator. Wait for the cycle to complete and the chamber to depressurise. Remove the pack or device with heat-resistant gloves. Compare the indicator against the colour reference printed on the pack, different manufacturers use different colour systems, so always compare against the right chart.
Step 6: Log the result. HTM 01-05 paragraph 4.17:
“These outcomes should be recorded in the logbook together with the date and signature of the operator.”
Date, cycle number, pass/fail, the temperature and pressure shown on the autoclave’s printout, your signature. Where the indicator strip can be peeled off and stuck into the logbook, do so. Records must be kept for at least two years (paragraph 4.12).
Bowie-Dick pass. A single uniform colour right across the indicator sheet, edge to edge, including the geometric centre. No streaks, no pale patches, no halo of paler colour around a darker centre or vice versa.
Helix pass. Complete uniform colour change from the start colour to the end colour across the whole indicator strip, including the end of the strip that sits inside the capsule at the closed end of the tube. If steam got to the deepest point of a 1.5-metre lumen, you’re fine.
Four patterns to recognise on a Bowie-Dick fail:
On a Helix fail, the indicator strip remains at the start colour at the capsule end, meaning steam didn’t traverse the full tube. The strip can look completely fine for the first half and fade at the end.
HTM 01-05 paragraph 4.21 is the load-bearing instruction:
“If the sterilizer fails to meet any of the test requirements, it should be withdrawn from service and advice should be sought from the manufacturer and/or maintenance contractor. Any instruments processed in an unsuccessful cycle should not be used.”
Practical sequence, in order:
Don’t panic, repeat the test once. Most false failures come from a cold chamber, a damaged indicator strip, or the wrong cycle being selected. Run a warm-up cycle, fit a fresh test pack, and try again.
Still failing? Stop using it for clinical loads. No instruments go through the machine until it passes. Any instruments processed since the last passing test should be considered non-sterile and re-processed.
Diagnose the easy stuff. Check the door seal hasn’t got a hair, a glove tip or a piece of pouch material caught in it. Confirm the test pack isn’t expired or damaged. Confirm the right cycle’s selected. Confirm there was nothing else in the chamber.
Still failing? Call your service engineer. Most pump or valve issues are external-engineer territory.
Record everything in the logbook: the failure, what you tried, what fixed it, when the engineer came, when the machine returned to service, the date of the first passing test after the failure.
Worth knowing because the alternative is paying for a call-out that turns out to be operator error.
STERIS’s troubleshooting guide flags the warm-up explicitly: it’s the most commonly missed step, and the false failures it produces are entirely preventable with a five-second fix.
A passing Bowie-Dick or Helix test doesn’t mean every cycle that day will be sterile. It means the machine’s air-removal stage is working at the moment of the test, on an empty chamber, with a worst-case challenge pack. Subsequent cycles depend on the instruments being cleaned properly first, packaged correctly, loaded so steam can circulate, and the cycle running to completion. The morning test gets you the green light to start using the machine. The rest is on you and your team.
If you’ve worked through the steps above and the test still won’t pass, give us a ring on 01274 265566. We diagnose the difference between “operator-fixable in five minutes” and “needs a real engineer visit” on the phone before sending someone out, most calls resolve in the conversation.
For the longer picture on what HTM 01-05 actually requires from a dental practice, our HTM 01-05 validation explainer walks through the whole compliance regime. If a CQC inspection is on the horizon, the practical CQC inspection guide is the sibling article.
