Particle release from respirators, part I: determination of the effect of particle size, drop height, and load.

In late 2001, some U.S. Postal Service workers and a few members of Congress were exposed to anthrax spores. This led to an increased effort to develop employable methods to protect workers from exposure to anthrax. Some investigations focused on selection and use of respirators to protect workers against airborne anthrax. The present study evaluated the potential for several types of half-mask respirators to release deposited particles. Four brands of the most commonly used filtering facepiece respirators (hereafter termed masks) were loaded with 0.59-µm, 1.0-µm, and 1.9-µm polystyrene latex (PSL) microspheres (nominally 0.6, 1.0, and 2.0 µm) and then dropped onto a rigid surface. The load conditions were 10, 20, or 40 million particles, and drop heights were 0.15, 0.76, and 1.37 m. For the average conditions of 0.76 m, 1.15 µm size and 22 million particles loaded, the average particle release was 0.604 particles per 10,000 (95% CI: .552, .662) particles loaded for all of the filtering facepieces tested. The averaging of conditions is a useful tool to provide generalized information and is also useful when making risk estimates. For most filtering facepiece respirators, particle release tended to increase with drop height and particle size, and there appeared to be a slight inverse relationship with particle load. Two brands of reusable elastomeric half-mask respirators with P100 high-efficiency particulate air (HEPA) filter cartridges were also evaluated. Results of these tests were inconclusive. Part II in this issue addresses the release of particles when simulating removal of a filtering facepiece from a wearer's head.

Particle release from respirators, part II: determination of the effect of tension applied in simulation of removal.

This study evaluated the potential for disposable filtering facepiece respirators (hereafter termed masks) contaminated with 1-µ m particles to release particles as a result of lateral tension applied to the mask. The lateral tension was designed to simulate the removal of a contaminated mask from a user's head. Four brands of filtering facepieces were loaded with approximately 20 million 1.0-µ m polystyrene latex (PSL) microspheres. The respirators were then placed in a test chamber and subjected to lateral tension between 17.8-26.7 N (4-6 lbs) for 1 to 2 sec. The findings suggest that neither mask type nor loading condition affects particle release. This supports our hypothesis that when filtering facepiece respirators are properly removed from the head they will not release a significant number of particles.

Design, demonstration and performance of a versatile electrospray aerosol generator for nanomaterial research and applications.

Carbon nanotubes are difficult to aerosolize in a controlled manner. We present a method for generating aerosols not only of carbon nanotubes, but also of many reference and proprietary materials including quantum dots, diesel particulate matter, urban dust, and their mixtures, using electrospraying. This method can be used as a teaching tool, or as the starting point for advanced research, or to deliver nanomaterials in animal exposure studies. This electrospray system generates 180 microg of nanotubes per m(3) of carrier gas, and thus aerosolizes an occupationally relevant mass concentration of nanotubes. The efficiency achievable for single-walled carbon nanotubes is 9.4%. This system is simple and quick to construct using ordinary lab techniques and affordable materials. Since it is easy to replace soiled parts with clean ones, experiments on different types of nanomaterial can be performed back to back without contamination from previous experiments. In this paper, the design, fabrication, operation and characterization of our versatile electrospray method are presented. Also, the morphological changes that carbon nanotubes undergo as they make the transition from dry powders to aerosol particles are presented.

Small airways response to naturalistic cat allergen exposure in subjects with asthma.

BACKGROUND: It is currently unclear whether the small airways (diameter <2 microm) contribute significantly to late asthmatic reactions to inhaled allergen. OBJECTIVES: We sought to determine whether naturalistic exposure to cat allergen induced late responses in the small airways as measured by pulmonary function testing and high-resolution computed tomography (HRCT) of the chest performed at end-expiration. METHODS: In a group of 10 subjects with cat-induced asthma, physiologic studies (spirometry and lung volumes, including closing volume) and HRCT were performed before and 6 and 23 hours after a cat room challenge that caused a 20% or greater acute fall in FEV(1). RESULTS: There was no significant decline in FEV(1) at 6 or 23 hours after cat exposure. Forced expiratory flow at 25% to 75% of forced vital capacity was significantly decreased at 6 hours after the challenge and returned to normal by 23 hours. HRCT image analysis as well as closing volume demonstrated increased air trapping from baseline at both 6 and 23 hours after the challenge. In addition, image analysis demonstrated a significant increase in small airways hyperresponsiveness to methacholine at 23 hours after the challenge. No significant mean changes were noted in lung volumes at either 6 or 23 hours or in PC(20) FEV(1) at 23 hours postchallenge. CONCLUSION: These findings demonstrate that naturalistic exposure to cat allergen results in significant small airways obstruction and hyperresponsiveness persisting for at least 23 hours, at which time these changes cannot be detected by conventional physiologic measures. CLINICAL IMPLICATIONS: Physiologically silent distal lung inflammation persists after an antigenic challenge.

Release of simulated anthrax particles from disposable respirators.

A preliminary study was undertaken to evaluate the potential for a disposable respirator that has been contaminated with anthrax spores to release spores in handling after use. The release of inert particles from disposable respirators was measured for masks dropped 3 feet onto a hard surface. Ten experimental runs were conducted for each of two N95 mask types, the Moldex 2200N95 and the 3M 8210. Anthrax spores were simulated with a test aerosol of single and double 1-micron polystyrene spheres. For the Moldex mask loaded with approximately 20 million spheres on it, an average of 0.16% was released; for the 3M mask an average of 0.29% was released.