NIOSHTIC-2 Publications Search

Variability in respiratory protection and the assigned protection factor.

Authors
Nicas M; Neuhaus J
Source
J Occup Environ Hyg 2004 Feb; 1(2):99-109
NIOSHTIC No.
20029310
Abstract
The workplace protection factor (WPF) for a given respirator wearer shows substantial variability from wearing to wearing; this variability is commonly assumed to be lognormal in nature. Further, when multiple WPFs are measured for each of multiple wearers, the aggregated WPFs appear to follow a lognormal distribution. However, the analysis typically applied to WPF data does not apportion variability within versus between wearers. We present an analytical framework based on a normal random effects model of log-transformed penetration P values (P = 1/WPF). Data from seven studies of negative-pressure air-purifying half-mask respirators, and from two studies of hemlet-and-visor type powered air-purifying respirators were analyzed by the method of maximum likelihood in the context of the model. More specifically, analyses were performed for log-transformed P values and for logit-transformed P values. Parameter estimates included within-wearer and between-wearer variance components. In general, the within-wearer component dominated the between-wearer component. We also propose a method for establishing an assigned protection factor, APF, that properly accounts for these variance components. Our method provides an APF satisfying two criteria: (1) for a given wearer, an acceptable WPF distribution has no more than 5% of WPFs below the APF value; and (2) for a wearer population, no more than 5% of wearers have unacceptable WPF distributions. The method incorporates an one-sided confidence limit to account for sampling variability. Alternative confidence limits were computed based on large sample variance estimates of random effects model parameters versus a bootstrap method. In general, there was good agreement between the APF values based on log-transformed versus logit-transformed P data, and between APF values based on the large sample variance estimates versus the bootstrap method. Based on large sample variance estimates for the logit-transformed P data from the seven half-mask studies, estimated APFs ranged from 1.4 to 250, with 5/7 studies yielding an APF <= 5.3. Given these results and related considerations, we recommend that the current half-mask APF be reduced from 10 to 5.
Keywords
Statistical-analysis; Models; Respirators; Air-contamination; Respiration; Air-purification; Air-purifiers; Air-purifying-respirators; Personal-protective-equipment; Protective-equipment; Respiratory-protection; Respiratory-protective-equipment; Microorganisms; Bacterial-dusts
Contact
Mark Nicas, PhD, Center for Occupational and Environmental Health, School of Public Health, University of California, Berkeley, California 94720
CODEN
JOEHA2
Publication Date
20040201
Document Type
Journal Article
Email Address
mnicas@berkeley.edu
Funding Amount
412603
Funding Type
Grant
Fiscal Year
2004
Identifying No.
Grant-Number-R01-OH-003570
Issue of Publication
2
ISSN
1545-9624
Priority Area
Research Tools and Approaches: Control Technology and Personal Protective Equipment
Source Name
Journal of Occupational and Environmental Hygiene
State
CA
Performing Organization
University of California, Berkeley, California
Page last reviewed: August 1, 2022
Content source: National Institute for Occupational Safety and Health Education and Information Division