A process challenge device, a helix test and a DART test are three different objects, and clinic procedures routinely blur them. A process challenge device (PCD) is a holder that creates a defined challenge and carries the indicator into it; the helix test is the hollow-load PCD specified for small steam sterilizers of Type B and Type S under EN 867-5; and DART stands for Daily Air Removal Test, a Type 2 air removal indicator system specified under ANSI/AAMI/ISO 11140-4 that is used on pre-vacuum sterilizers at the start of the working day. None of the three is a biological indicator, and none of them replaces the daily spore test. This article separates the three, sets out what each one proves, and maps the tests by sterilizer type.
Quick facts
- A PCD is a device, not a test result. It creates a defined penetration challenge - a lumen, a coil, a cavity - and holds the chemical or biological indicator in the location judged least accessible to the sterilizing agent.
- The helix test is the hollow-load test for Type B and Type S small steam sterilizers, specified in EN 867-5 as an indicator system and process challenge device for performance testing. Small steam sterilizers themselves are covered by EN 13060, whose current edition is BS EN 13060:2025.
- DART means Daily Air Removal Test. It is a Type 2 air removal indicator system meeting ANSI/AAMI/ISO 11140-4, used on pre-vacuum (dynamic air removal) sterilizers at the beginning of each day the sterilizer is used.
- A Class 2 air removal test is a daily requirement, not a periodic one. Saskatchewan's CDSS standards require the air removal test at the beginning of each day that a dynamic air removal sterilizer is used, placed in an empty chamber per the manufacturer's instructions, typically on the bottom shelf above the drain.
- Hollow instruments are the reason all of this exists. A hollow lumen can hold an air pocket that the chamber sensor never sees, so the load's least accessible location has to be challenged deliberately rather than assumed to have been reached.
What is a process challenge device
A process challenge device is a test device that provides a defined challenge to the sterilizing agent, into which a chemical indicator or a biological indicator is placed. The point of a PCD is that it stops the indicator from being tested in easy conditions. An indicator sitting loose on a shelf sees whatever the chamber sees; an indicator inside a PCD sees what an instrument lumen, a wrapped tray or a dense textile pack sees.
In Ontario practice the PCD appears in two requirements at once: the biological indicator requirement is expressed as a test placed in a challenge device, and the internal chemical indicator requirement as placement in the area judged least accessible to steam penetration - which, the guidance notes, is not necessarily the centre of the package. A dental office running a bare indicator loose in the chamber is not running either test as written.
PCD designs are not interchangeable. A helix coil, a porous test pack and a lumen tray create different challenges, each matched to a purpose:
| PCD form | Challenge | Typical indicator | What it targets |
|---|---|---|---|
| Helix or hollow-load device | Long narrow lumen | Chemical indicator or biological indicator | Steam penetration into tubular and hollow instruments; Type B and Type S small sterilizers |
| Porous test pack | Porous load with air removal demand | Type 2 air removal indicator | Air removal on pre-vacuum cycles |
| Process challenge tray or container | Structured cavity and load geometry | Chemical indicator or biological indicator | Routine load monitoring for trays, cassettes and containers |
| Indicator with integrated challenge | Manufacturer-defined lumen or cavity | Biological indicator | Daily spore testing where the indicator itself carries the challenge |
What is a helix test and which sterilizers need one
The helix test is a hollow-load test: a coiled tube of defined length and internal diameter that steam has to penetrate to reach the indicator at its far end. EN 867-5 specifies indicator systems and process challenge devices for use in performance testing for small sterilizers of Type B and Type S, and the hollow-load test for small steam sterilizers corresponding to Type B is the test defined in that standard. Manufacturer descriptions of helix devices agree on the function: a helix test is classified as a process challenge device for evaluating the air removal and steam penetration capability of a Type B sterilizer.
The sterilizer side sits in EN 13060, which defines small steam sterilizer classes and their requirements and testing; the current edition is BS EN 13060:2025. This is why the helix test is associated with dental benchtop sterilizers rather than large hospital units: it is the equipment performance test for the class that dental offices use. Large sterilizers under EN 285 use the same hollow-load principle within a different test framework.
An important distinction for a clinic running both a helix test and a daily spore test: they answer different questions. The helix test asks whether the sterilizer can drive steam into a long narrow lumen - an equipment capability. The spore test asks whether the cycle killed resistant spores in the place the indicator was put. A sterilizer can pass one and fail the other, and neither result is a statement about the other.
What is a DART test
DART is the Daily Air Removal Test, a Type 2 air removal indicator system. Published product specifications describe these test packs as meeting the requirements of ANSI/AAMI/ISO 11140-4 for Type 2 air removal indicator systems and operating at 132 to 134 C with an exposure time of 3.5 to 4.0 minutes. The international standard behind the class is ISO 11140-4, which specifies performance for a Class 2 indicator used as an alternative to the Bowie and Dick-type test for steam sterilizers.
Three things follow from that description.
First, a DART test is an air removal test, not a sterility test. It detects poor air removal and therefore poor steam penetration on a pre-vacuum cycle. It does not contain spores and cannot report on spore lethality.
Second, it is a pre-vacuum test. Air removal tests exist because dynamic air removal cycles depend on removing air before steam is admitted; gravity displacement cycles do not work the same way, and the daily test does not apply to them in the same form.
Third, it is a daily test with its own placement rule. Saskatchewan's standards require the air removal test at the beginning of each day the sterilizer is used, performed in the chamber of an empty sterilizer as per the manufacturer's instructions, which is typically on the bottom shelf above the drain. Placing it in a loaded chamber falsifies the test, because the load itself changes air removal behaviour.
How do the three tests differ
| Question | Process challenge device | Helix / hollow-load test | DART (air removal test) |
|---|---|---|---|
| What is it | A holder that creates a defined penetration challenge | A hollow-load PCD with a coiled lumen | A Type 2 air removal indicator system |
| What it carries | A chemical or biological indicator | A chemical or biological indicator | Its own air removal indicator |
| Standard | Specified by the process and indicator standards in use | EN 867-5 for Type B and Type S small sterilizers | ANSI/AAMI/ISO 11140-4; ISO 11140-4 for the class |
| What it proves | That the indicator faced a realistic challenge | That the sterilizer can penetrate a long narrow lumen | That air was removed adequately on a pre-vacuum cycle |
| Frequency | Every biological indicator test and every package's internal indicator | Per the sterilizer's requirements and the facility's test schedule | Each day the sterilizer is used, on pre-vacuum cycles |
| Does it replace the daily biological indicator | No | No | No |
| Failure signal | Indicator fails at the challenge position while chamber parameters passed | Indicator fails at the far end of the lumen | Uneven or incomplete colour change |
How often is each test run in Ontario
The frequency of the tests comes from the regulator and from provincial guidance, and each one sits on its own clock.
- Biological indicator: each sterilizer, every day it is used. Ontario guidance is that spore testing must be done each day the sterilizer is used, with a control test recorded alongside. Public Health Ontario adds the cycle dimension: a biological indicator each day of use and with each type of cycle used that day.
- Air removal test: each day the sterilizer is used, on dynamic air removal sterilizers. Performed in an empty chamber at the beginning of the day, before loads are processed.
- Internal chemical indicator: every package, container and bundle. Placed in the area judged least accessible to steam penetration; the class is chosen according to the parameters being measured and the precision required.
- External chemical indicator: every package, examined immediately after sterilization to distinguish processed from unprocessed items.
- Hollow-load and performance testing: per the sterilizer's specified test schedule and the applicable equipment standard, alongside planned maintenance.
A clinic that runs the daily air removal test but skips the hollow-load test has validated one failure mode and not the other; a clinic that treats a helix test as its daily monitoring requirement has confused an equipment test with load monitoring. Both belong on the same calendar, in different rows.
What should the record show
Provincial standards set a floor for in-house monitoring records: the sterilizer, the date, the time and the signature of the staff member completing the process. Air removal test results belong in the same record set with the test type identified, and package indicators are recorded as part of load release rather than in a separate log.
For a clinic assembling the consumables for all four rows at once, the Bowie-Dick style test pack covers the daily Type 2 air removal requirement on pre-vacuum sterilizers, Class 4 dual-indicator pouches cover the external and internal chemical indicator requirement in one article, and the daily spore test itself runs on a 24-hour self-contained 25-pack or, for a shorter readout workflow, a 3-hour fluorescence indicator. A 5-pack trial is the smallest start if the daily routine is new.
Sources
- W&H helix test page, helix test as a PCD for Type B sterilizers - checked 16 September 2026
- GKE process challenge devices for small steam sterilizers, hollow load test per EN 867-5 - checked 16 September 2026
- BSI Knowledge, BS EN 13060:2025 small steam sterilizers - checked 16 September 2026
- SIST EN 13060:2025, small steam sterilizers - checked 16 September 2026
- Fisher Scientific listing, DART daily air removal test per ANSI/AAMI/ISO 11140-4, 132-134 C - checked 16 September 2026
- ISO 11140-6:2022, Type 2 indicators and process challenge devices for small steam sterilizers - checked 16 September 2026
- ISO 11140-1:2014, chemical indicators - general requirements, third edition - checked 16 September 2026
- CDSS provincial infection prevention and control standards for oral health care, monitoring sterilization - checked 16 September 2026
- CDSS page-numbered revision copy, daily indicator, daily control, weekly mail-in test - checked 16 September 2026
- Public Health Ontario PIDAC cleaning, disinfection and sterilization guidance, 3rd edition, 2013 - checked 16 September 2026
- RCDSO, infection prevention and control in the dental office: some common issues - checked 16 September 2026
- ISO 17665:2024, moist heat sterilization requirements - checked 16 September 2026
- ANSI/AAMI/ISO 11138-1:2017, general requirements for biological indicators - checked 16 September 2026
- EN ISO 11138-3:2017, biological indicators for moist heat - checked 16 September 2026
- ISO 11139:2018, sterilization vocabulary - checked 16 September 2026
- Vatanparast et al., biological indicator failure rates in Saskatchewan dental practices, BMC Oral Health 2024 - checked 16 September 2026
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
The Ontario-specific case for challenge devices is set out in why Ontario dental offices use a process challenge device, and the daily pre-vacuum test is compared brand by brand in Bowie-Dick test packs compared. The indicator inside the challenge is covered in Class 4 versus Class 5 versus Class 6 chemical indicators, and the whole monitoring chain is mapped in our sterilization compliance hub.
Related Reading
- Why Ontario dental offices use a process challenge device
- Bowie-Dick test packs compared
- Class 4 versus Class 5 versus Class 6 chemical indicators
- Sterilization compliance hub
- free Ontario sterilization compliance log
Frequently Asked Questions
Is a process challenge device a biological indicator
No. A process challenge device is a holder that creates a defined penetration challenge, and a biological indicator or chemical indicator is placed inside it. The PCD determines where the indicator is tested; the indicator determines what is measured. Ontario's biological indicator requirement places the indicator in a challenge device, and the internal chemical indicator requirement places it in the area judged least accessible to steam penetration.
What is the difference between a helix test and a Bowie-Dick test
A Bowie-Dick type test is an air removal test for pre-vacuum sterilizers, run in an empty chamber at the start of the day. A helix test is a hollow-load test in which steam must penetrate a long coiled lumen to reach the indicator, used as the performance test for Type B and Type S small steam sterilizers under EN 867-5. One targets air removal from a porous load, the other targets steam penetration into a narrow lumen.
What does DART stand for in sterilization
Daily Air Removal Test. It is a Type 2 air removal indicator system meeting ANSI/AAMI/ISO 11140-4, used on pre-vacuum sterilizers at the beginning of each day the sterilizer is used. Published specifications for these test packs give an operating range of 132 to 134 C with an exposure time of 3.5 to 4.0 minutes. It contains no spores and is not a substitute for the daily biological indicator.
Do I need a helix test if I already run a daily spore test
They test different things. The daily spore test monitors whether the cycle killed resistant spores where the indicator was placed; the helix test is an equipment performance test of the sterilizer's ability to penetrate a long narrow lumen, tied to the sterilizer's test schedule and its type under EN 13060 rather than to daily monitoring.
Where should the air removal test be placed
In the chamber of an empty sterilizer, following the manufacturer's instructions for use - typically the bottom shelf above the drain. Saskatchewan's CDSS standards state this placement directly. Running it in a loaded chamber changes air removal behaviour and does not answer the question the test exists to ask.
Can a Class 5 or Class 6 chemical indicator replace the PCD
No. An integrating or emulating chemical indicator responds to the cycle variables it is exposed to wherever it is placed, which is exactly why placement matters. The PCD supplies the challenge - a lumen, a cavity, a porous structure - and the indicator inside it reports what happened in that challenge location. Using a chemical indicator without a challenge device tests an easier condition than the load presents.
How does a hollow instrument fail sterilization without the sterilizer reporting an error
A hollow lumen can retain an air pocket the chamber sensor never sees, because the sensor measures the chamber, not the inside of the instrument. Steam cannot reach a surface that air occupies, so lethality inside the lumen can be far lower than the recorded chamber parameters suggest. Hollow-load and challenge device testing reproduces that geometry deliberately.
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