Dust Masks

[K P Steinmeyer <publish@gyral.com>]

Joe Archer asked about the use of dust masks.

NRC is in the process of amending its regulations (10 CFR 20 Subpart H and Regulatory Guide 8.15) to (among other things) permit the use of filtering facepieces (i.e., "dust masks").  Under NIOSH's relatively new certification system for negative-pressure air purifying respirators (42 CFR 84), all such filtering facepieces are at least 95% efficient, although non-NIOSH-certified "comfort masks" of uncertain efficiency are still available.  A thorough explanations of this certification system can be found in Steinmeyer, K. Paul. "NIOSH Approval Requirements for Respiratory Protection Equipment."  Radiation Protection Management Vol. 15, No. 5, Sept/Oct 1997.

NRC is considering treating filtering facepieces in two groups, which I'll refer to here as upper division and lower division.  Upper division filtering facepieces have adjustable straps AND a rubber (or plastic) seal-enhancing material applied to the entire face-sealing surface.  Also, most of the upper division devices have an exhalation valve, but the presence of one of these is not considered critical.  All other filtering facepieces would be considered to be in the lower division.  NRC would consider the upper division devices to be half facepieces with APF = 10, as recommended by ANSI, as long as all other program requirements are met (medical screening, training, fit testing, etc.).  Lower division facepieces would not be given an APF but could be used with an APF = 10 if all the program elements, including fit testing, are in place.  

Licensees, however, will be able to use lower division facepieces (NOT upper division) on a VOLUNTARY BASIS without medically screening or fit testing the volunteer users, as long as they are provided with a very brief and basic training program (possibly 5 minutes long).  This practice is also permitted by OSHA.  Respirator use is voluntary when one is not required, but workers request a device.  It sounds like carrying a filtering facepiece for ALARA reasons in case an unexpected release were to occur would be an appropriate application for these devices.

In your case, a NIOSH-certified device should be used.  While it may cost a bit more than 50-cents, it is a real respirator designed to fit well and to remove a large percentage of airborne particulate contaminants.  Don't use a medical or surgical mask since there is no requirement for these to be NIOSH certified, and they are just not designed for an industrial environment.  All NIOSH-certified filtering facepieces are REAL RESPIRATORS, and will be much more effective than a surgical mask or a shirt wrapped around a person's face.

These filtering facepieces are designed to be reuseable, within reasonable limits, so a new one would probably not be required each day or each shift.  The carrying of such devices by workers, to be used in case of a release, is certainly ALARA, and the upcoming revision of Subpart H would require that ALARA be the determining factor for assigning (or not assigning) respirators to workers.  Professional discretion would also be given a lot of weight in NRC's new scheme.

As a point of clarification, the term HEPA is not and never was applied to respirator filters.  Under NIOSH's old rule (30 CFR 11) dust-fume-mist respirators were required to be 99.97% efficient at collecting 0.3 micron particles generated by hot DOP, but the term HEPA is not found.  NIOSH now permits the use of NaCl and non-thermally generated DOP to test filter media, since hot DOP presents an exposure problem to the test equipment operators.

The NRC's proposed new table of assigned protection factors (APFs) are consistent with those listed in ANSI Z88.2-1992.  While these may be conservative, there is potentially a vast difference between quality of fit obtained during fit testing and average quality of fit maintained in the workplace.  The efficiency of the filter medium isn't the problem.  It's the face-to-facepiece seal that is the weak link, and in the workplace average fit factors (when they can be measured) are often dramatically lower than those obtained during fit testing.  NRC's new rule would contain clear guidance on what constitutes an acceptable fit before the APF can be applied in the field.

Further input from Radsafers on this and related topics would be most welcome.

K. Paul Steinmeyer, RRPT
Senior Health Physicist

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