The TST Helix is a Hollow Load Process Challenge Device (PCD) as defined in EN 867-5 and has been developed and validated for testing the air removal (steam penetration) capability of small Type B steam sterilizers only.

Use in any other sterilizer or with any other type of indicator, may give dangerously misleading results. A successful test confirms steam penetration through the helix and confirms by implication that air and other non-condensable gases have been removed.

The chemical indicator located in the capsule will show a defined colour change from yellow to dark blue / purple when exposed to a specific combination of time, temperature and steam. When all air has been removed from the sterilizer chamber, steam will penetrate through the helix and the indicator will show a uniform colour change. If air or noncondensable gases are present they will impair contact between the steam and the indicator resulting in a non-uniform colour change; distinct yellow markings will be evident on the indicator.

The TST Helix has a limited life, so after 250 indicators have been used, the device must be replaced. Failure to do so could result in failure of the device and dangerously misleading results.