Influence of facial hair length, coarseness, and areal density on seal leakage of a tight-fitting half-face respirator

J Occup Environ Hyg. 2018 Apr;15(4):334-340. doi: 10.1080/15459624.2017.1416388.


Background: OSHA regulations state that an employer shall not permit tight-fitting respirators to be worn by employees who have facial hair that comes between the skin and facepiece seal. Studies have shown that facial hair in the face seal zone can increase penetration and decrease the fit factor (FF), although the relationship between the amount and characteristics of facial hair and the increase in penetration is not well quantified. This article examines the influence of facial hair length, areal density, and coarseness on FF for one model of half-face elastomeric negative-pressure air purifying respirator.

Approach: Quantitative fit tests (QNFT) were performed on 19 subjects with beards initially 0.500-in long and subsequently trimmed to 0.250, 0.125, and 0.063 in, then after a razor shave. Three fit tests were performed at each of the 5 lengths, for 285 total tests. The average diameter and areal density of cheek and chin hair were measured. Penetration was modeled as a function of hair length category, beard areal density, and hair coarseness.

Results: FF decreased with beard length, especially beyond 0.125 in. However, passing FF scores were achieved on all tests by all subjects at the smooth shave and 0.063 in conditions, and 98% of tests were passed at 0.125 in; seven subjects passed all tests at all conditions. Chin and cheek areal densities were significantly different and were only weakly correlated. Beard hair diameters were normally distributed across subjects (mean 76 µm, standard deviation 7.4 µm). Beard length and areal density, but not coarseness, were statistically significant predictors of fit using an arcsine transformed penetration model. FF decreased with increasing beard length, especially beyond 0.125 in, although FF with a "stubble" beard did not differ significantly from a smooth shave. FF also decreased with increasing areal beard hair density.

Conclusion: Beard length and areal density negatively influence FF. However, tight-fitting half-face negative-pressure respirator fit tests can achieve adequate fit factor scores even with substantial facial hair in the face seal area.

Keywords: Beard; elastomeric; facial hair; leakage; penetration; respirator.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Face*
  • Hair Removal
  • Hair*
  • Humans
  • Male
  • Middle Aged
  • Pilot Projects
  • Respiratory Protective Devices*