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Health Hazards of Smoke Winter/Spring 1992

Risk Management

Proposed NFPA Respirator Standard

The proposed NFPA standard for respiratory protection for wildland firefighters will be available for public comment in August. The proposed standard is intended to provide relief from some of the contaminants found in the firefighting environment. The standard will not provide protection from all sources of airborne contaminants in forest fire smoke, which include carbon monoxide, respirable particulate, and organic gases. Approved air purifying respirators do not provide relief from carbon monoxide. The universal or type "N" canister provides protection from all three hazards, but that device is not approved by the National Institute for Occupational Safety and Health (NIOSH) for firefighting activities. Therefore, the respirator user must be thoroughly trained in the use and limitations of the device. They must not develop a false sense of security while wearing the respirator. Crews will have to monitor carbon monoxide levels to avoid overexposure.

The proposed NFPA standard should be viewed as the basic standard of protection for wildland firefighters, to be worn at the discretion of the worker. Agencies may develop regulations that mandate use when minimum exposures are exceeded. Lightweight inexpensive devices that meet the proposed standard are available. Higher levels of protection can be achieved with more expensive devices (full-face, powered air-purifying respirators or PAPR), and protection from organic gases can be added by using sorbents along with the proposed level of protection. Thus, the standard will meet the basic needs of wildland firefighters, while allowing additional protection for those who regularly encounter higher levels of exposure (e.g., during prescribed burns).

Mouthpiece Respirator

The small, lightweight mouthpiece respirator is approved for escape use only from specific hazardous atmospheres (chlorine, sulfur dioxide, etc.). Some firefighters have asked about the use of these devices during wildland firefighting. With the proper filter and/or sorbent, it would appear to be a possible alternative for firefighters (Figure 3). However, mouthpiece respirators have been restricted to escape use only by NIOSH. One reason is that the nose clip provided with the< device interferes with the sense of smell and masks the warning properties of gases. Another reason for restriction could be a concern for the fit and function of the devices. The following abstract addresses those issues.

Photo of a mouthpiece respirator.
Figure 3—Mouthpiece respirator.

Quantitative Fit Testing Of Personnel Utilizing A Mouthpiece Respirator. L. Packard, H. Brady, and O. Schumm (C. O'Leary et al, ed.) in Respiratory Protection, Akron: American Industrial Hygiene Association, 1985.

Fifty volunteers participated in a comparison of a mouthpiece respirator and half-face respirators. Fit tests were conducted before and after a 30-day test period. When used in a chlorine plant work situation, the half-face respirator offered less protection than the mouthpiece respirator. The half-face respirator was inferior in an emergency exposure. It interfered with vision and communication and required removal of the hard hat to put on. It was judged less handy, more awkward to use, and generally less effective in keeping out contaminated atmospheres. The user had to remain clean-shaven to assure an acceptable fit. A small portion of the population could not be fit with a half-face respirator because of their facial configuration. While a few individuals with dentures had difficulty with the mouthpiece respirator, the authors strongly recommended that the mouthpiece respirator be allowed equal status with the half-face respirator for use in the chlorine plant work situations.

For Wildland Firefighters? With the proper filter and/or sorbent for intermittent use in atmospheres that are not considered immediately dangerous to life and health, the mouthpiece respirator would seem to be a useful option for wildland firefighters who are difficult to fit, have facial hair, or wear glasses. Existing devices would need a larger airway to accommodate the ventilation associated with the vigorous work of firefighting. However, such a device is not currently approved for extended wear by NIOSH.

Effect Of Facial Hair On Respirator Performance. E. Hyatt et al., in Respiratory Protection,, Akron, OH: American Industrial Hygience Association, 1985.

The effect of facial hair on the performance of half-mask and full-face respirators was measured with a quantitative aerosol test system. Different test subjects having varying degrees of facial stubble, sideburns, and beards were used in the study. Test results showed that the effect of facial hair on the performance of a respirator depends upon the degree to which the hair interferes with the sealing surface of the respirator, the physical characteristics of the facial' hair, the type of respirator worn in relation to the subject's facial characteristics, and other factors. It is concluded that persons with excessive facial hair such as facial stubble, sideburns, and beards, which interfere with the respirator seal, cannot expect to obtain as high a degree of respirator performance as persons who are clean shaven. [Note: The major drop in respirator performance occurs in the first 3 days of beard growth, with variable but continued degradation in performance thereafter.]

Carbon Monoxide Exposure

Carbon monoxide (CO) is a colorless, odorless product of incomplete combustion. When inhaled, it competes with oxygen for space on the hemoglobin molecule, thereby reducing oxygen transport. Prolonged exposure leads to elevated levels of carboxyhemoglobin (COHb) in the blood. The following table summarizes some of the effects of exposure.

COHb% Effect
1.0 No apparent effect
1 to 2 Some effect on behavioral performance
2 to 5 Central nervous system effects: Impairment of line interval discrimination,
  Visual discrimination (sharpness/brightness),
  Psychomotor function (coordination)
5.0 Cardiac and pulmonary function changes
10 to 20 Headaches, fatigue, drowsiness, nausea, dizziness
50 to 60 Intermittent convulsions
70 to 80 Coma, cardiovascular failure, and death
Note: Symptoms may be present at levels below or above those indicated. Non-smokers may experience headaches and nausea at levels well below 10 percent COHb.

The maximal safe exposure for firefighting personnel is considered to be 5 percent COHb, a level achieved after 8 hours of exposure at 50 ppm. With the strenuous effort of firefighting, increased respiration shortens the time to equilibrium. Therefore, the 8-hour time-weighted average of 35 ppm recommended by NIOSH for CO exposure seems more appropriate for wildland firefighters. The short-term exposure' limit is 200 ppm, which would lead to 5 percent COHb in a short period of exposure. Since no currently approved air purifying respirator provides protection from carbon monoxide, firefighters must be well acquainted with the symptoms of exposure and crews should monitor CO levels to avoid overexposure.

Maximal work capacity is diminished at levels above 4 percent COHb, but there is little immediate effect on submaximal work at levels below 15 percent COHb. Of course, CO exposure accentuates symptoms in those with heart and respiratory disease. Carbon monoxide is additive with the effects of altitude and CO lowers the body's resistance to work in the heat. COHb levels are slow to decline when the worker leaves the contaminated atmosphere. As a general rule, levels decline 50 percent every 3 hours. Removal can be accelerated by breathing oxygen. Some symptoms (e.g., visual) can persist after COHb levels have been reduced. For more information on carbon monoxide, refer to previous editions of this report.

Lower Carbon Monoxide Standard for Firefighters? NIOSH investigators believe that the 35 ppm standard for exposure to carbon monoxide (CO) may not be protective for wildland firefighters. The 35 ppm standard is designed to keep COHb levels below 5 percent in most workers. However, since that standard is based on an 8-hour work shift, low energy expenditure and air intake, and low elevations, the standard may not be appropriate for firefighters engaged in arduous work for long shifts, sometimes at higher elevations. Using values appropriate for wildland firefighters in Yellowstone Park, NIOSH researchers calculate that the 5 percent COHb level could be reached at an exposure concentration of 17 ppm (time weighted average for 12-hour shift). For more information, consult Health Hazard Evaluation Report, HETA 88-329-2176, USDI National Park Service, Yellowstone National Park. C. Reh and S. Deichtman, NIOSH.

Tent Reduces Particulate

MTDC is evaluating a personal tent as a means of improving the sleeping environment for firefighters. The tent provides protection from cold, moisture, insects, smoke, and dust. Preliminary tests conducted by Dave Blakeley at the Intermountain Fire Sciences Laboratory indicate that particulate levels are 25 times higher outside the tent when compared with samples collected inside the shelter, indicating a 96 percent reduction in exposure to particulate. The 35 square-foot semi-freestanding tent has received field evaluation and is currently undergoing modification. Tents should be available from GSA for the 1993 field season. For information, contact Ted Putnam or George Jackson at MTDC (406-329-3967).

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