Particle shedding of cleanroom garments: Helmke drum test and categories
Cleanroom garments are meant to contain particles but must not shed any themselves. How much a garment sheds is measured by the Helmke drum test according to the recommended practice IEST-RP-CC003. This guide explains the method, the classification into Categories I to III and how to read data sheet figures correctly.
At a glance
- The Helmke drum test tumbles a garment in a rotating drum and counts the particles released per minute.
- Category I (below 1,200 particles ≥ 0.3 µm per minute) is the best level and standard for ISO 4 to 6.
- The values apply to the tested sample; seams, zips and use increase shedding.
- Compare only values with the same particle size, method and condition (new or laundered).
- Related products: coveralls, cleanroom socks, masks.
How the test works
The garment is placed in a stainless steel drum that rotates at a defined speed. Tumbling makes fabric, seams and closures rub against each other, as happens when worn. A particle counter draws air from the drum and counts the particles above a certain size, usually from 0.3 µm or 0.5 µm. The result is given as particles per minute, mostly as an average over several minutes.
The test comes from the recommended practice IEST-RP-CC003 of the Institute of Environmental Sciences and Technology, which treats cleanroom garments comprehensively: material selection, construction, testing, laundering and use. It is not a standard test in the sense of an EN but has established itself worldwide as the benchmark.
Categories I to III
| Category | Particles ≥ 0.3 µm per minute | Usual assignment |
|---|---|---|
| I | below 1,200 | ISO 3 to 5, also ISO 6 |
| II | 1,200 to 12,000 | ISO 6 to 7 |
| III | 12,000 to 120,000 | ISO 7 to 8 |
The assignment to ISO classes is guidance from the recommended practice, not a rule. Which category your room requires is set by the contamination control strategy. High-quality single-use garments made of laminate usually reach Category I; many manufacturers also state the measured values, for example 743 particles per minute from 0.3 µm, which makes the classification traceable.
Reading data sheets correctly
- Particle size: values from 0.3 µm are higher than from 0.5 µm; compare only equal sizes.
- Condition: single-use garments are tested new, reusable garments after a certain number of washes. A value without the condition is of little use.
- Test object: was the whole garment, a set or only the material tested? Seams and zips increase shedding.
- Typical or guaranteed: many data sheets state typical values. Guaranteed limits per lot are rare; ask for them if your qualification needs them.
- Target or measured value: for new products data sheets often contain design targets. On prosafe-cleanroom.eu we label these explicitly as target specifications.
Further tests for particulate cleanliness
The drum test measures the shedding of the garment. How well a garment system shields the person is shown by the body box test (dispersal chamber): a person performs defined movements in a chamber while particles are counted. For gloves, IEST-RP-CC005 applies, measuring particles and ions from the surface. Material tests such as air permeability and hydrostatic head complete the picture but say nothing directly about particles.
What increases shedding in operation
- Moving too fast and rubbing against edges.
- Damaged seams, open adhesive flaps on the zip.
- Wrong size: strain pulls fibres out of the material.
- Wearing single-use garments more than once.
- Everyday clothing with a high fibre content under the coverall.
Check your garments not only in the data sheet but in the room: particle measurements at workstations in operation show whether system and behaviour match.
Conclusion
The Helmke drum test makes particle shedding comparable when size, condition and test object match. Category I is the requirement for ISO 4 to 6 and the design target for the new ProSafe cleanroom line. We supply the measured values of the series with the test report.
Read on: Choosing cleanroom gloves: material, length, double gloving and test values
More in the knowledge section
Go deeper into individual topics: cleanroom classes, garment system, sterility, particle shedding, gloves, masks and standards.
