Evaluation of a passive method for determining particle penetration through protective clothing materials

ABSTRACT

The risk of workers' exposure to aerosolized particles has increased with the upsurge in the production of engineered nanomaterials. Currently, a whole-body standard test method for measuring particle penetration through protective clothing ensembles is not available. Those available for respirators neglect the most common challenges to ensembles, because they use active vacuum-based filtration, designed to simulate breathing, rather than the positive forces of wind experienced by workers. Thus, a passive method that measures wind-driven particle penetration through ensemble fabric has been developed and evaluated. The apparatus includes a multidomain magnetic passive aerosol sampler housed in a shrouded penetration cell. Performance evaluation was conducted in a recirculation aerosol wind tunnel using paramagnetic Fe³O⁴ (i.e., iron (II, III) oxide) particles for the challenge aerosol. The particles were collected on a PVC substrate and quantified using a computer-controlled scanning electron microscope. Particle penetration levels were determined by taking the ratio of the particle number collected on the substrate with a fabric (sample) to that without a fabric (control). Results for each fabric obtained by this passive method were compared to previous results from an automated vacuum-based active fractional efficiency tester (TSI 3160), which used sodium chloride particles as the challenge aerosol. Four nonwoven fabrics with a range of thicknesses, porosities, and air permeabilities were evaluated. Smoke tests and flow modeling showed the passive sampler shroud provided smooth (non-turbulent) air flow along the exterior of the sampler, such that disturbance of flow stream lines and distortion of the particle size distribution were reduced. Differences between the active and passive approaches were as high as 5.5-fold for the fabric with the lowest air permeability (0.00067 m/sec-Pa), suggesting the active method overestimated penetration in dense fabrics because the active method draws air at a constant flow rate regardless of the resistance of the test fabric. The passive method indicated greater sensitivity since penetration decreased in response to the increase in permeability.

KEYWORDS:

• Aerosol
• penetration
• protective fabric
• sampler
• test method

Acknowledgments

The authors acknowledge Mr. Tony Rozzi and Ms. Lisa Barkand formerly with NIOSH for conducting experiments; NIOSH colleagues Teresa Barone, Teh-hsun B. Chen, and Ziqing Zhuang for reviewing this article. Dr. Pengfei Gao served as the project officer during the time this data was collected.

Disclaimer

The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health. Mention of any company or product does not constitute endorsement by NIOSH. The authors identify no conflicts of interest in the conduct of this study.