Testing the protective performance of clothing materials against aerosols

In AEP 38, skin protection against aerosol particles offered by CBRN protective equipment is recognized as an important issue that has to be verified. The work presented here focuses on material (i.e. swatch) tests, as opposed to whole system tests that use mannequins or human volunteers and which also include leakage and clothing design. No internationally accepted test standards exist to determine aerosol protection by clothing, but many swatch tests based on filter tests and some cylinder tests have been developed. The filtration tests mainly differ in challenge aerosol, test flow rate, forced flow or free flow due to wind, and sampling strategy. Cylinder tests differ for example in the way the fabric is draped around the cylinder, the size of the cylinder and the direction of the air flow around the cylinder. TNO has developed a filtration method based on vapour penetration tests according to NATO AEP-38 and a cylinder test in which deposition is measured. We have identified the most important properties of the clothing and critical test procedure parameters in both tests. A comparison has been made with a filtration test developed by WIS, Germany. Filtration efficiency and air flow resistance of the material appear to be the key parameters in a cylinder test. Air flow resistance determines the flow velocity through the cloth at a given wind speed and influences the deposition of aerosol onto the skin underneath the clothing thus influencing the protective performance of clothing materials. Filter efficiency improves, sometimes dramatically, with increasing particle size. Also the choice of flow rate, which can be set to a standard value or dependent on the cloth air flow resistance, is an important parameter, with efficiencies usually decreasing with increasing flow velocity through the cloth. There is a strong correlation between the cylinder test and the filter test results.