Document Type


Date of Degree

Spring 2019

Degree Name

MS (Master of Science)

Degree In

Occupational and Environmental Health

First Advisor

O'Shaughnessy, Patrick

First Committee Member

Nonnenmann, Matthew

Second Committee Member

Fethke, Nathan


According to the Occupation Safety and Health Administration (OSHA), an estimated five million workers are required to wear respirators in over one million workplaces in the United States. Occupational respiratory diseases are strongly correlated to inhalation exposure to causative agents. Wearing a respirator has the potential to reduce worker exposure to safe concentrations. Many brands of N95 filtering facepiece respirators (FFRs) are available with various designs and sizes. Studies have indicated that respirator use is often low in many industries. Comfort is a factor that workers use both directly and indirectly to decide if they will wear an FFR. The purpose of this study was to evaluate ten N95 FFRs to determine their physical properties. Physical properties were compared to the perceived comfort ratings given by study participants to determine the strength of the associations. Six FFRs were evaluated using qualitative surveys (n=50).

Physical properties of FFRs that were evaluated include: breathability, pressure drop, surface area, water vapor transmission and weight. Several methods were used to evaluate the N95 physical properties. A modified American Society for Testing and Materials (ASTM) method was used to measure water vapor transmission. A pass through column apparatus was used to evaluate pressure drop through each sample at 0.6, 1.6, 2.6, and 3.6 LPM. The N95 FFRs were scanned and evaluated using Adobe Photoshop to determine surface area. A temperature probe was used to measure the influence of an exhalation valve on internal temperature. An inverted microscope was used to determine thickness, a balance was used to determine sample weight. Density could then be used to solve for solidity. Physical properties varied between N95 FFRs. Between two similar FFRs, the exhalation valve was attributed to a 0.59 oC lower temperature in the FFR with and exhalation valve. Pressure drop values at a 3.6 LPM applied flow rate varied between 4.55-12.77 mm H2O. The water vapor transmission between masks was very small with a range of 0.16 mg H2O. Solidity values varied between 0.02 and 0.07, surface area from 134.95- 313.87, and total weight from 9.47-109.41 g. The total scores varied from 10.76 to 14.26 (out of 18).

Survey participants were asked to evaluate the N95 FFRs on the basis of fit, temperature, and ease of breathing using a Likert scale of 1-6. Six of the N95 FFRs were worn by participants. Based on participant rankings, the Honeywell 4200 had the highest total score, followed by the Moldex 4200, 3M Aura 9210+, 3M 8511, Moldex 2200, and 3M 8210. The scores for fit varied from 3.16-4.36, temperature 3.66-5.24, and ease of breathing 3.94-4.66. Fit was found to be the most important in terms of discomfort followed by temperature, and ease of breathing.

The Kruskal-Waillis test results indicate that there is a significant difference in the median scores between masks types for fit, temperature, and ease of breathing (p<0.001). However, participants’ rankings of fit, temperature, and ease of breathing were not strongly related to a physical property. For example, the Spearman’s correlation coefficient between pressure drop and ease of breathing score was 0.2, and 0.6 for water vapor transmission and temperature. Neither Spearman’s coefficient was statistically significant (p=0.7, p=0.2).

In general, the differences in physical properties between N95 FFRs were too small for participants to perceive. The magnitude of difference in physical properties and short use duration and sedentary activity level are likely responsible for this finding.


x, 71 pages


Includes bibliographical references (pages 69-71).


Copyright © 2019 Matthew Purdy