What is the Helix test and how is it performed in an autoclave?
— Equipo JP Selecta
The Helix test is a physico-chemical process indicator designed to verify an autoclave's ability to drive saturated steam right into the interior of long, narrow cavities with blind ends. In the day-to-day running of a laboratory or clinic, it is a critical test when working with tubular instruments, cannulas, contra-angle handpieces or dental instruments, as well as glass or plastic pipettes and test tubes with complex geometry.
Unlike the Bowie-Dick test (which examines air removal and steam penetration in porous loads such as textiles or wrapped packs), the Helix test simulates the physically most demanding scenario in terms of geometry. To do so, it uses a test device consisting of a 1.5-metre-long helical PTFE tube with an internal diameter of barely 2 millimetres, connected at one end to a capsule housing an indicator strip. For the steam to reach that reactive strip, the autoclave must be capable of removing with total efficiency the air trapped inside that narrow duct.
This test is governed by EN ISO 11140-4 (which specifies the characteristics of indicators for Helix-type tests) and by the EN 13060 standard (for small steam sterilisers, where the Helix test is established as the approval test for type A hollow loads).
In which autoclaves is the Helix test mandatory?
The Helix test applies exclusively to autoclaves with a fractionated vacuum system (Class B), both in small sterilisers (EN 13060) and in large autoclaves (EN 285).
There is no point in carrying it out in gravity displacement autoclaves (conventional Class N or S), since these units do not generate the vacuum pulses needed to extract the air retained inside cannulated materials.
| Autoclave class | Helix test applicable? | Standard |
|---|---|---|
| Class B (fractionated vacuum) | Yes | EN 13060, EN 285 |
| Class S (specified by the manufacturer) | In some cases | EN 13060 |
| Class N (gravity displacement) | No | EN 13060 |
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How do you carry out the Helix test?
Remember that in the laboratory safety is essential. Carrying out a Helix test is no exception.
To ensure the reproducibility of the test and its full validity in quality audits or GMP certifications, it must be carried out following these steps, with safety and prevention in mind:
- Make sure the chamber is empty: the autoclave must be completely free of loads, additional baskets or working instruments.
- Position the test device: insert a reactive strip into the capsule of the Helix device and place it on its own on the lower tray of the chamber, oriented according to the manufacturer's specifications (usually near the condensate drain point).
- Select the test programme: choose the specific Helix cycle in the unit's menu (usually programmed at 134 ºC, 2.1 bar and a short pre-vacuum cycle).
- Run the cycle: Start the process and keep the door locked until it has fully finished.
- Cooling and opening: remove the device using protective gloves and wait for the capsule to cool.
- Reading and filing: open the capsule, take out the reactive strip and compare the colour change with the reference chart from the commercial kit. File the strip together with the date and the cycle number.
Interpreting the Helix test results
Visual assessment of the indicator strip determines whether the unit is fit to operate with hollow loads:
Correct result: complete colour change of the indicator
The ink of the reagent changes colour uniformly across the whole length of the strip. This confirms that the air was successfully removed from the 1.5-metre tube and that saturated steam reached the capsule at the far end. The autoclave is safe for processing cannulated or tubular instruments.
Incorrect result: indicator with no colour change or only a partial one
The strip does not change colour or shows discontinuous areas. This indicates that air remained trapped inside the tube and prevented the steam from entering. The unit must not be used to sterilise hollow loads until the problem has been resolved.
The possible causes of a Helix test failure include leaks in the door seal, loss of performance in the vacuum pump or the presence of non-condensable gases in the steam supply. If the failure persists after a second test, the unit must be taken out of service for technical inspection.
When is the Helix test carried out?
It is advisable to carry out this check in the following circumstances:
- At the start of the working day, after the vacuum test (leak test) and before the first sterilisation cycle.
- After maintenance work, the replacement of seals or repairs to the vacuum system.
- After prolonged periods of inactivity of the installation.
- If anomalies are detected during the pre-vacuum phase in the readings on the pressure gauge or display.
A correct Helix test result depends as much on the procedure as on the autoclave itself: only correctly calibrated fractionated vacuum units guarantee the air removal needed in complex cavities.
J.P. Selecta autoclaves incorporate fractionated pre-vacuum systems and automatic cycle logging that make it easier to carry out and document the Helix test in accordance with the EN 13060 standard and GMP requirements. For more information about maintaining your equipment, you can consult our technical services.