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Performance of N95 respirators: reaerosolization of bacteria and solid particles.

Qian Y; Willeke K; Grinshpun SA; Donnelly J
Am Ind Hyg Assoc J 1997 Dec; 58(12):876-880
A study of the propensity for respirators to reaerosolize bacteria and other particles while being worn in environments contaminated with airborne bacteria or other pathogens was conducted. The filters of N95 half mask respirators were loaded with sodium- chloride or polystyrene latex (PSL) particles, or Bacillus-subtilis or Bacillus-megatherium, used as surrogates for Mycobacterium- tuberculosum (surrogate TB bacteria) having aerodynamic diameters of 0.1 to 5 micrometers (micron) at a flow rate of 85 liters per minute (min) for 30 to 50min. The respirators were then mounted in a specially designed apparatus and the extent of reaerosolization of the particles off the filters was determined at reentrainment velocities ranging up to 400 centimeters per second (cm/sec). The experiments were conducted at 25 degrees-C and the relative humidity (RH) in the air flows varied up to 35% or more. The number of reentrained particles were counted by a dynamic aerosol size spectrometer. The number of reaerosolized particles was determined by subtracting the number of particles measured during loading of the filter from those counted during reentrainment. Reaerosolization of the sodium-chloride, PSL, and surrogate TB bacteria particles amounted to less than 0.05% for particle sizes below 1micron, RHs of 22% or less, and reentrainment velocities up to 300cm/sec. Reaerosolization of the surrogate TB bacteria, which had aerodynamic diameters of 0.8 to 1.0micron, was generally around 0.02% under these conditions. Increasing the PSL particle size to 5micron increased the proportion of reaerosolized particles to 6 to 7% at a reentrainment air flow of 300cm/sec. Increasing the reentrainment velocity to 400cm/sec, caused a slight, but nonsignificant increase in the proportion of reaerosolized surrogate TB bacteria particles. No particle reaerosolization was seen under any conditions for RHs of 35% or greater. The authors conclude that reaerosolization of particles and bacteria collected on the fibrous filters of N95 respirators is insignificant at conditions normally encountered in respirator wear. When the respirator wearer coughs or sneezes at exhalation velocities on the order of 200cm/sec, some of the particles and bacteria could become airborne. Further studies should be conducted to determine whether bacteria can reproduce on respirator filters and, if so, whether the new bacteria can be reaerosolized from the filters.
NIOSH-Publication; NIOSH-Grant; Respirators; Aerosol-particles; Biohazards; Respiratory-protective-equipment; Air-filters; Air-flow; Microorganisms; Laboratory-testing; Author Keywords: efficiency; filter; microorganism; Mycobacterium tuberculosis; reaerosolization; respirator
Environmental Health University of Cincinnati 3223 Eden Ave Cincinnati, OH 45267-0056
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Journal Article
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Respirator Research; Respirators
Source Name
American Industrial Hygiene Association Journal
Performing Organization
University of Cincinnati, Cincinnati, Ohio
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division