Results of a recently completed NIOSH study confirm the necessity of the current Occupational Safety and Health Administration (OSHA) respirator fit testing requirement, both annually and when physical changes have occurred. The study’s conclusions emphasize that respirator users who have lost more than 20 pounds should be re-tested to be sure that the current size and model of respirator in use still properly fits. For over three years, NIOSH researchers followed a cohort of 229 subjects measuring N95 filtering facepiece respirator (FFR) fit and physical characteristics (e.g., face size, weight) every six months. Prior to this study, very little research existed looking at the relationship between respirator fit over an extensive period of time and the change in facial dimensions, as could be caused by weight gain or loss. OSHA requires FFR users to undergo an annual fit test, which is vital to ensuring continued proper respirator fit. In addition to annual fit testing, OSHA requires that fit testing be repeated “whenever an employee reports, or the employer or the physician or other licensed health care professional makes visual observations of changes in the employee’s physical condition that could affect respirator fit (e.g. facial scarring, dental changes, cosmetic surgery, or an obvious change in body weight.” (OSHA, 1998)
The appropriate length of time between respirator fit tests has been a point of debate and discussion for many years. Fit testing can be time-consuming and a burden to workplace resources (Zhuang, 2015). OSHA addressed these concerns in 1998 when publishing the respiratory protection standard (OSHA, 1998). During the public comment period for OSHA’s rulemaking, data from four companies were considered in establishing the annual fit test requirement. Three of the companies reported <3% of employees failed fit testing after 1 year and one company conducting biannual fit tests found that 7% of their employees switched to different sizes or models because of a failed fit test. OSHA considered a two-year 7% failure rate unacceptable (meaning that a high percentage of employees could be relying on poor-fitting respirators if not fit tested annually), and thus supported an annual fit testing requirement (OSHA, 1998).
In 1999, NIOSH endorsed all provisions of OSHA’s 29 CFR Part 1910.134 relating to the frequency of fit testing (NIOSH). Despite this endorsement, questions surrounding the frequency of respirator fit testing remained from employers (e.g., especially those in the healthcare sector) and the industrial hygiene community. Examples are located in the comments to a previous NIOSH science blog on this topic titled Frequency of Respirator Fit Testing. In response to these continued concerns, NIOSH initiated a study to address three primary questions:
- Does respirator fit change over time?
- Does weight change cause respirator fit change?
- Is annual fit testing necessary?
NIOSH conducted a pilot study of 10 subjects to investigate the variation in fit test data to assess the background failure rate. The subjects were tested in order to match them with a properly-fitted respirator. The subjects repeated the tests two and four weeks after the initial tests. Adequate fit was maintained for all 10 subjects during this time period. After conducting this pilot study, researchers were ready for the three-year large scale study that would examine the link between how often someone is fit tested and the changes in N95 FFR fit when weight fluctuation occurs and alters facial dimensions. More detailed background information for reporting of this pilot study can be found in a previous NIOSH Science Blog titled Frequency of Respirator Fit Testing and in the manuscript published in the Journal of Occupational and Environmental Hygiene (Zhuang et al., 2011).
Subjects were recruited from a group of study volunteers used for certification testing and physiology studies, as well as from the general public in southwestern Pennsylvania.
Researchers focused on FFRs because they are the most commonly-worn respirator used in the healthcare industry and the necessity of annual fit testing for these types of respirators is often debated. The study included seven different sizes and models of N95 FFRs, all of which were purchased for the CDC Strategic National Stockpile at the time the study was initiated.
The researchers were interested in measuring the fit factor, which tells the researcher whether a respirator fits the subject properly or not. Subjects qualified for the study by demonstrating acceptable fit for one of the N95 FFR models in the study. They then used samples from that same FFR model for the remainder of the study. Fit factors from nine donnings (putting on the respirator) were measured and physical characteristics of the subjects were captured approximately every 6 months for a 3 year period.
Of the 229 subjects that initially enrolled in the study, 134 completed all seven visits. Data was omitted for subjects who participated in only the first visit, leaving 195 subjects who participated in two or more visits. Subjects were categorized by face length and width and the researchers determined that the distribution of facial dimensions of the 195 participants were a good representation of the general U.S. workforce (Zhuang, 2007 & Zhuang 2005).
The estimated percent of workers whose respirator did not fit them increased with increasing length of time between fit tests, from 10% at Year 1 to 20% at Year 2, doubling those at risk for exposure if not fit tested, and to 26% at Year 3. This exceeds the 7% threshold used by OSHA in 1998 during rulemaking. Additionally, twenty-four percent of subjects who lost more than 20 pounds no longer maintained an acceptable fit.
This study found that respirator fit did change over time. The greater the weight loss, the higher the chance that respirator fit will change. Therefore, this NIOSH study supports the current OSHA requirement for annual fit testing. Additionally, respirator users who lose more than 20 pounds since his or her last fit test should prioritize scheduling a fit test to ensure proper respirator fit. Though further research is necessary, because of the similarity in face seal between other tight-fitting respirators and FFRs, these findings may be applicable not only to FFRs but also to other tight-fitting respirators. The full NIOSH study titled, “Temporal Changes in Filtering-Facepiece Respirator Fit”, is published in the Journal of Occupational and Environmental Hygiene and can be accessed through Taylor & Francis Online.
Dr. Zhuang is the Material and Equipment Performance Team Leader in the Research Branch at the NIOSH National Personal Protective Technology Laboratory (NPPTL).
Mr. Bergman is an Associate Service Fellow in the Research Branch at the NIOSH National Personal Protective Technology Laboratory
Ms. Krah is a Health Communication Specialist in the NIOSH National Personal Protective Technology Laboratory.
U.S. Occupational Safety and Health Administration: Respiratory Protection, 29 CFR 1910.134: Final rule. Federal Register Notice. 63:1152-1300 (1998).
Zhuang, Z., M. Bergman, E. Brochu, A. Palmiero, G. Niezgoda, X. He, R. Roberge, and R.E. Shaffer: Temporal Changes in Filtering Facepiece Respirator Fit. JOEH. 2015 (ePub ahead a print, DOI: 10.1080/15459624.2015.1116692).
U.S. Institute of Medicine: Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users. Washington, DC: The National Academies Press, 2007
Zhuang, Z., Benson, S., Lynch, S., Palmiero, A., & Roberge, R. (2011). Laboratory study to assess causative factors affecting temporal changes in filtering facepiece respirator fit: Part I–pilot study. Journal of occupational and environmental hygiene, 8(12), 729-739.
Zhuang, Z.Q., B. Bradtmiller, and R.E. Shaffer: New Respirator fit test panels representing the current US civilian work force. J. Occup. Environ. Hyg. 4(9): 647-659 (2007).
Zhuang, Z.Q. and B. Bradtmiller: Head-and-face anthropometric survey of US respirator users. J. Occup. Environ. Hyg. 2(11): 567-576 (2005).
NIOSH . NIOSH Policy Statement: NIOSH Respirator Use Policy/OSHA’s I91 0.1 34. August 4, 1999. http://eid.niosh.cdc.gov/policystatement/pdfdoc/PSZY38W.pdf