Aerodynamic adsorption of permeable chemical protective suit

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

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.

Validation and application of the personnel factor for the garment used in cleanrooms

The cleanroom environment has many potential sources of contamination, including: operators, equipment, structures, and any surface that can create particles via friction, heat, exhaust, outgassing, and static electricity charge. Operatives working in the cleanroom are the major source of particles. While cleanroom operators work, they emit millions of particles from every activity. Particles migrate up the cleanroom garment to the head and drop to the legs during cleanroom movements. Specialized textile fabrics have been used in cleanroom garments for many years. The need for this type of fabric has increased mainly due to the need to protect critical operations in cleanrooms as well as creating comfort for operators and other personnel. This study covers the general static wind-driven method, the Helmke Drum method and the dispersal chamber to measure particle penetration, shedding, and generation, in regards to the filtration efficiency of cleanroom fabrics and garments. Firstly, particle penetration is shown to increase with increasing face velocity and decreasing particle size below 1 μm. Secondly, that a recommended upper particle-size limit should be 5 µm. Using the Helmke drum test, the size distribution of particles released from the garment is shown to follow a power law distribution, with a slope of less than 1. Furthermore, the study introduces dynamic body box for testing fabrics as well as cleanroom garments. It is more practical and sensitive when compared to traditional methods and is based on a more concise technical approach. The life-time cycle performance of a typical cleanroom garment coverall is examined, particularly looking at the implications of pre-use steralization.