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N95 mask may provide less protection than believed
Some say face seal leakage as high as 20%
As cases of severe acute respiratory syndrome (SARS) decline worldwide, questions remain about one of the major tools for protecting health care workers: Just how effective is the N95 filtering facepiece respirator?
Some respiratory protection experts are calling for a lower rating, or "assigned protection factor" (APF), for the N95 to reflect the leakage of air around the face seal. The N95 actually allows as much as 20% leakage, not the 10% reflected in its current rating, the experts say. After evaluating studies of the filtered facemasks and other respirators, the U.S. Occupational Safety and Health Administration recently proposed keeping the APFs at their current level.1
"A 5 is more appropriate for a filtering facepiece," says Roy McKay, PhD, director of the occupational pulmonology services program at the University of Cincinnati College of Medicine and a respiratory protection expert. "Because of the real-life experience [of workers using the respirators], I feel the value of 10 is not justified."
The debate has implications for hospital respiratory protection programs and the selection of respirators to protect against highly infectious diseases, such as SARS. An APF indicates how much of the contaminated air is filtered by the respirator. With an APF of five, there is five times less contaminant inside the respirator than in the surrounding air.
Conduct respirator fit tests annually
The APF is influenced by real-life work conditions. Inadequate fit testing and training diminish the quality of respiratory protection at many hospitals, McKay says. "The need for fit-testing of respirators isn’t universally accepted by many hospital employees or administrations," McKay says.
Hospitals should conduct annual fit tests, even if the respirators are used only for TB, McKay asserts. OSHA set up a respiratory protection standard for TB (1910.139) that was intended to be temporary while the agency drafted a tuberculosis standard. That proposed standard has since been withdrawn.
"As it stands now, TB is the only agent that has respiratory protection practices different from every other chemical and biological agent," he says. "That really makes very little sense."
Workers cannot tell how effective the face seal is by simply checking it visually or manually, he says. "There are many cases where a person puts on a respirator and it appears to fit, yet when we do quantitative fit-testing, it does not," says McKay, who conducts fit-testing training seminars and consults with hospitals. "If someone like myself, who has vast fit-testing experience, is unable to visually identify respirators that do and don’t fit, there’s no way that other people with less experience would be able to do that."
APFs are commonly used at industrial work sites, where exposure levels are measured and only respirators with adequate characteristics are allowed. But hospitals also rely on the APF to ensure the proper level of protection for health care workers exposed to highly infectious agents.
Mark Nicas, PhD, MPH, CIC, adjunct associate professor of environmental health sciences at the University of California-Berkeley School of Public Health, analyzed seven studies on the filtering facepieces and provided consultation to OSHA. "The data were very variable. We concluded an assigned protection factor of 5 rather than 10 was a better value," he says.
Different masks rated differently
That view was confirmed by a committee accredited by the American National Standards Institute and sponsored by the American Industrial Hygiene Association. The panel of industry representatives and respiratory protection experts proposed setting the APF for filtering facepieces at 5.
"They’re not all the same," says Howard Cohen, PhD, CIH, associate professor of occupational safety and health at the University of New Haven (CT) and chair of the ANSI Z88.2 committee that considered the standard. "As a group, we gave them a 5. If we were allowed to rate them individually, we would have come up with some 10s."
In its Federal Register notice, OSHA cites another review of studies of filtering facepieces that indicated the respirators should have an APF of 10.
"OSHA is aware of discussions within the respirator community indicating some sentiment for setting APFs for filtering facepiece respirators at 5, and for setting an APF of 10 for other half-mask air-purifying respirators," the agency stated in the Federal Register notice. "Based upon OSHA’s reviews, OSHA cannot differentiate between the performance of the two types of respirators, and OSHA finds compelling evidence from the large number of observed data points to support proposing an APF of 10 for both of these classes of respirators."
OSHA requested comment on its methodologies and conclusions. In its explanation, OSHA also noted that proper fit is critical to achieving the higher protection factor.
For hospitals, that means investing in several brands so as to provide the best fit for the largest number of employees, says McKay. Cost should not be the overriding criterion, he stresses.
"When I do fit-testing in hospital employees, [I’m] just not going to find one particular make and model that’s going to fit everybody. People have unique facial features, and people need different respirators," he says.
"If a program administrator correctly identifies which respirators fit a large percentage of the population, you may be able to capture your entire work force in two or three different models," he says.
Cohen recommends conducting quantitative fit-testing using an N100 of the same style as the N95. That would ensure the maximum performance from this type of respirator, he says. "I think doing quantitative fit-testing is well within the scope and capability of hospitals," he says.
Filtering facepiece respirators have come under scrutiny in hospital outbreaks of SARS in Canada. Toronto hospitals used N95-type respirators that were not certified by the National Institute for Occupational Health, a branch of CDC. Hospitals did not routinely conduct fit-testing of employees.
In one difficult intubation of a SARS patient, six health care workers who were in the room and wearing protective gear later developed SARS symptoms.2 Interestingly, the health care worker who intubated the patient "was never really recognized as having any symptoms. He was only in there for the intubation, and he wore two masks, one over the other," says Clifford McDonald, MD, a SARS investigator from CDC. "He may have just been very careful and didn’t get any inoculum. But when we questioned him, he did say he thought he maybe had one or two days of cough afterward, but very briefly. [It] lasted one or two days [and he] never documented a fever.
"He would be a very important person to get a serology from later on," noted McDonald. "Maybe this can all be traced back to an inoculum, and if you get a low enough inoculum you’ll get immunity and very minimal symptoms. Beyond that, it’s all speculation."
During high-risk procedures, such as intubation, the N95 may not be adequate, says Nicas. "In my personal opinion I don’t think the filtering facepieces are protective enough, especially in procedures that are going to produce a lot of aerosolized fluid," he says.
McKay notes that going to a higher filtration — an N99, for example — will not address the issue because the same rate of leakage will occur around the face seal. "If one recognizes a need for a higher level of protection, you go to a more protective respirator," he says.
In June, the Ontario Ministry of Health and Long-term Care issued a directive to acute care hospitals requiring a powered air-purifying respirator or other full-face respiratory protection to be worn along with an N95 during high-risk procedures such as intubation.
The Ontario Nurses Association also has demanded fit-testing for all nurses who wear respirators and has urged the Ministry of Labour to ensure that hospitals are providing fit-testing. At North York General Hospital, one nurse refused to work because her mask did not fit properly.
[Editor’s note: For more information about respiratory protection workshops, contact Roy McKay at (513) 558-1234
1. U.S. Occupational Safety and Health Administration. Assigned protection factors: Proposed rule. 68 Fed Reg 34,036-34,119 (2003).
2. Ofner M, Lem M, Sarwal S, et al. Cluster of severe acute respiratory syndrome cases among protected health-care workers — Toronto, Canada, April 2003. MMWR 2003; 52:433-436.
Respirator Facts and Myths
1. OSHA requires fit-testing for all tight-fitting respirators, including single-use filtering facepieces (i.e., N95s), when required to be worn. [FACT]
2. The sweetener fit test method (saccharin) is accepted as a validated fit test method, without the need to determine the wearer’s level of sensitivity to the sweetener first. [MYTH]
3. Fit-testing with hand-held banana oil ampules is an OSHA-accepted (i.e., validated) method for fit-testing respirators. [MYTH]
4. Fit-testing with amyl acetate (banana oil) using validated techniques, such as those recommended by ANSI, requires testing to be performed in at least two rooms that have separate ventilation systems. [FACT]
5. OSHA, ANSI, and NIOSH recommend fit-testing for ALL tight-fitting respirators, including positive-pressure respirators such as SCBAs, air-line, PAPRs, etc., when required to be worn. [FACT]
Source: Roy McKay, PhD, director of the occupational pulmonology services program at the University of Cincinnati College of Medicine.