for people ages 18 years and up (full criteria)
Healthy Volunteers
healthy people welcome
at San Francisco, California
study started
estimated completion
Principal Investigator
by Maria C Raven, MD
Headshot of Maria C Raven
Maria C Raven



During critical personal protective equipment (PPE) shortages, such as those associated with the COVID-19 pandemic, Centers for Disease Control (CDC) recommends N95 extended use (wearing the same N95 for multiple patient encounters) and limited reuse (storing an N95 between shifts for use over multiple shifts with or without decontamination) as contingency and crisis capacity strategies, respectively. Many healthcare workers (HCWs) are employing these strategies out of necessity. The sustained performance of these respirators depends on the respirator maintaining its filtration efficiency and its ability to provide an adequate seal (fit) to the user's face. Fit testing is performed when a respirator is issued to the user and on an annual basis thereafter. A user-seal check is then performed whenever a respirator is donned. Previous studies have found repeated donnings/doffings to significantly decrease the respirator's fit. A recent pilot cross-sectional clinical study conducted by the University of California, San Francisco found fit failures of respirators after being worn for 2 shifts. However, more definitive data regarding respirator performance during reuse and extended use are lacking. The investigators plan to address these critical gaps in knowledge by conducting a prospective cohort study to determine the incidence of N95 fit failure when subjected to extended use/reuse in a clinical setting. The investigators plan to enroll 396 ED providers (including physicians, nurses, and staff) when obtaining a new NIOSH approved N95s and performing serial fit tests at the end of each 8-12 hour shift for up to 5 clinical shifts or until N95 failure, whichever is earlier. By carefully measuring fit test failure in a clinical setting, the investigators will be able to provide guidance regarding the safety of N95 extended use and reuse necessitated by the need for PPE conservation. Specifically, the investigators will address the following research questions: 1) how long N95s maintain their fit during extended use, 2) how many times N95s can be donned/doffed and maintain their fit, 3) the ability of a user seal check to indicate fit in the field, 4) what adverse health effects, reports of discomfort, or symptoms are experienced by users during extended use and reuse, 5) what effect does extended use and reuse have on N95 filtration performance, 6) the level of contamination of N95s when subjected to extended use and reuse, 7) the effect of modifications to N95 (covering an N95 with a face shield or surgical N95s, facial coverings) on fit failure.

Official Title

A Clinical Examination of N95 Reuse and Extended Use


Frontline healthcare workers are at high risk of SARS (severe acute respiratory syndrome) CoV-2 (COVID-19) infection. Personal protective equipment (PPE), such as an N95 respirator (N95), is essential for prevention of COVID-19 among HCWs. N95s can prevent aerosolized transmission of viral particles and reduce COVID-19 among HCWs, helping to reduce infection rates and preserve the workforce. Under normal circumstances, the CDC recommends that HCWs dispose of N95s after a single patient encounter. However, during critical PPE shortages such as those during the current COVID-19 pandemic, the CDC recommends N95 extended use (wearing the same N95 for multiple patient encounters) and re-use (storing an N95 between shifts for use over multiple shifts). N95 shortages have been widely reported during the COVID-19 pandemic and have forced HCWs to practice extended use and reuse of N95s. Despite the CDC's guidelines, there are limited data regarding the efficacy of N95s under conditions of extended use and reuse and existing studies have been conducted in laboratory settings rather than in the actual health care environment. (Bergman 2012; Vuma et al 2019). This has left health care workers, including emergency department (ED) providers on the front lines of the COVID-19 pandemic, without clear guidance regarding N95 conservation. Many have implemented various reuse and extended use policies out of necessity but with no empirical evidence of their safety and effectiveness. The study team conducted a pilot cross-sectional study of 68 ED providers who wore either a 3M 1860 dome style N95 or a duckbill N951. 70.6% of duckbill N95 failed a standardized fit test with 3M bitter solution and a hood. Of the dome style , 27.5% failed a fit test. N95 failure was associated with increasing numbers of shifts used: There were 0/11 failures after 1 shift, 1/12 failures after 2 shifts, 3/13 failures after 3 shifts, and 10/15 failures after 4 or more shifts. Also, more donnings and doffings were associated with fit failure, with a median of 8 donning and doffings in the fit pass group and 15 donning and doffings in the fit failure group. This preliminary study had a number of limitations, including a small sample size, convenience sampling, and cross-sectional design, and so was unable to definitively identify the number of shifts or donnings/doffings for which N95s can be safely reused. The investigators propose to conduct a prospective cohort study of 396 participants across 6 ED sites to estimate the cumulative incidence of N95s when subjected to extended use and reuse in a clinical (emergency department) setting with fit test failure and contamination as the main endpoints. The investigators also seek to compare the fit test failure between varying types of HCWs wearing a number of N95 types. Additionally, the investigators will collect the N95s used in this study for additional analyses of at an outside laboratory measuring COVID-19 contamination levels and filtration efficiency.


Emergency Medicine, Frontline Providers, Healthcare Worker, N95 mask, Personal Protective Equipment, Extended use, reuse, Emergencies


You can join if…

Open to people ages 18 years and up

  • Adult (18 years old or greater)
  • ED providers (MDs, nurses, Advanced Practice Providers (APPs)) who are practicing extended use and re-use for the majority (more than half) of their shifts Participants are eligible when obtaining a new N95 and are scheduled to work a minimum of 5 shifts within a 60-day period. As hours of enrollment and data collection depend on research associate availability, participants working certain shifts may not be eligible.

You CAN'T join if...

  • Participant does not intend to use N95 for majority of shift
  • Schedule prohibits re-use and or data collection
  • Repeated failed baseline fit test
  • Refused or unable to consent
  • Pregnant
  • Facial hair (e.g., beards or sideburns) or jewelry which interferes with the face seal region of an N95


  • University of California, San Francisco accepting new patients
    San Francisco California 94143 United States

Lead Scientist at UCSF

  • Maria C Raven, MD
    Dr. Raven is a practicing Emergency Medicine physician and health services researcher, is the Chief of Emergency Medicine at UCSF and a Vice Chair in the UCSF Department of Emergency Medicine.


accepting new patients
Start Date
Completion Date
University of California, San Francisco
Study Type
Expecting 330 study participants
Last Updated