t .. United States 

Department of 

Agriculture 

Forest Service 

Pacific Northwest 

Research Station 

Research Paper 

PNW-RP-441 

October 1991 

Monitoring Firefighter Exposure to 

Air Toxins at Prescribed Burns of 

Forest and Range Biomass 

Timothy E. Reinhardt 
Author TIMOTHY E. REINHARDT is a scientist for Radian Corporation, 2121 4th Avenue, Suite 

280, Seattle, Washington, 98121. He was research scientist, U.S. Department of Agriculture, Forest Service, Fire and Air Resource Management Project, Seattle, Washington, 

98105, when the research was done. 
Abstract Reinhardt, Timothy E. 1991. Monitoring fireflghter exposure to air toxins at prescribed 

burns of forest and range biomass. Res. Pap. PNW-RP-441. Portland, OR: U.S. 

Department of Agriculture, Forest Service, Pacific Northwest Research Station. 8 p. 

A variety of potent air toxins are in the smoke produced by burning forest and range 

biomass° Preliminary data on flrefighter exposures to carbon monoxide and formaldehyde 

at four prescribed burns of Western United States natural fuels are presented. Formaldehyde may be correlated to carbon monoxide emissions. The firefighters' exposures to 

these compounds relative to workplace standards are discussed. 

Keywords: Firefighter health, air toxins, formaldehyde, carbon monoxide. 

Summary Many potent air toxins are in the smoke of burning forest and range biomass. Firefighters 

are exposed to the smoke of both wildfire and prescribed fire. A comprehensive assessment of these exposures is not yet possible due to insufficient data. Preliminary data on 

firefighter exposures to carbon monoxide and formaldehyde at four prescribed burns of 

Western United States natural fuels are presented. At these well-managed prescribed 

burns, occupational exposure limits for these compounds were not exceeded. In the exposure samples taken, formaldehyde was correlated to carbon monoxide emissions. The 

firefighters' exposures to these compounds relative to workplace standards are discussed. 
Contents 1 

1 

2 

6 

7 

7 

8 

8 

Introduction 

Experimental Methods 

Results 

Discussion 

Conclusions 

Research Needs 

Acknowledgments 

Literature Cited 
Introduction 

Experimental 

Methods 

Because firefighter exposures to the air toxins in smoke from prescribed burns and wildfires are not adequately understood, we have begun a study to achieve the following goals: 

(1) to obtain a first approximation of the exposures that firefighters face in different firecontrol situations; 

(2) to test the feasibility of personal monitoring methods, including passive dosimetry, in the 

complex fire environment; and 

(3) to evaluate the correlation between carbon monoxide and other air toxins in smoke. 

Prescribed fire is a tool commonly used by land managers today. Among its applications, 

fire is used to reduce wildfire hazard and competing vegetation in forested areas, as a site 

preparation before tree planting, and to improve forage value of range lands. The USDA 

Forest Service and other forest and rangeland managers employ many thousands of 

firefighters nationwide to manage these prescribed burns as well as to suppress wildfires. 

Firefighters can be exposed to several potent air toxins in the smoke from burning vegetative biomass. 

The atmosphere near the fire is complex and prone to interferences in sample collection 

and analysis. In addition to the extremes of heat and humidity near a large fire, the smoke 

contains hundreds of organic and inorganic combustion products. Of those that are toxic or 

carcinogenic in humans, few are present in high enough concentrations to pose a potential 

health threat. Earlier work has identified carbon monoxide (CO) as a potential health threat 

to firefighters (Jackson and Tietz 1989). In addition to CO, we have identified low-molecular-weight aldehydes (including formaldehyde [HCHO], acrolein, and furfural), respirable 

particulate (PM2.5), and benzene as potential firefighter health threats. Many polycyclic 

aromatic hydrocarbons (PAH) are also common components of the particulate phase of 

smoke. For validation, workplace monitoring methods for these compounds must be tested 

in the conditions that they will be used in. 

Monitoring of firefighter exposures to smoke was accomplished at four prescribed fires in 

October 1988 on the Lake Wenatchee District of the Wenatchee National Forest in central 

Washington. These were broadcast burns of debris (slash) left after clearcut logging in 

mixed-conifer stands ranging in size from 4 to 44 acres. The general burning plan for 

broadcast burns is to ignite the top and center of the unit to be burned, thereby forming a 

strong convection column that draws fresh air towards the center of the unit. The edges of 

the unit are then ignited, and the heat and smoke are carried towards the center, away 

from the firelines. About 20 to 30 flreflghters, 5 fitted with smoke sampling packs, were involved in each burn. 

The flrefighters' activities include several tasks: (1) lighting, which involved igniting the area 

to be burned by walking through the slash while dripping a burning mixture of gasoline and 

diesel fuel; (2) line holding, which requires the flrefighter to stand guard, often in smoke, to 

keep the fire within the boundaries of the burn area; (3) direct attack, which was a consequence of spot-fires ignited by sparks and brands blown across the fire line which the 

firefighter must then extinguish with a fire hose, axe, and shovel; and (4) mop-up, which 

occurs after the main burn is smoldering and involves extinguishing =hot spots." This work 

often continues for several days. 

The smoke sampling packs were flameproof, lightweight, and designed not to catch in 
Results 

heavy brush. Each pack contained a personal air-sampling pump (Gilian Instruments I) 

which drew air at approximately 300 milliliters per minute through an inlet at the firefighters' 

breathing zone. A C-18 sample clean up cartridge (Waters Associates), at the inlet, was 

impregnated with 2,4-dinitrophenylhydrazine. 

Aldehydes, including formaldehyde, were efficiently chemisorbed in this cartridge. At the 

laboratory, the cartridges were eluted with 2.0 milliliters acetonitrile and analyzed by liquid 

chromatography. Authentic aldehyde derivatives were prepared and recrystallized for use 

as standards (Hull 1985, Kuwata and others 1983). 

A constant fraction of the exhaust of the pump was used to fill an inert gas bag (Calibrated 

Instruments) over the sample period. The integrated gas sample collected was analyzed 

for CO by nondispersive infrared spectroscopy (Wilson and others 1983) by using a 

standard CO mix traceable to the National Bureau of Standards. Carbon monoxide 

samples were obtained sequentially from a firefighter over 0.5 to 1.5 hours during the 

burns; the duration depended on logistics and our visual estimates of the homogeneity of 

the smoke exposures at the time. The individual CO samples collected from a given 

firefighter in a day were time-weighted and averaged to derive exposures over 1.5 to 3 

hours, which was the total duration of the firefighters' exposures on this set of burns. The 

aldehyde samples were concurrently taken from each firefighter over 1.5 to 3 hours. 

Sampling was not meant to statistically describe the exposures of the firefighters, but to 

test method performance and obtain estimates of the concentration ranges to be expected. 

In addition to the above two active sampling methods, two commercial dosimeters were 

compared for their performance at monitoring HCHO and CO on the same subjects and 

time periods. These were direct-reading passive diffusion tubes from Sensidyne and 

Draeger, respectively. These devices are sealed glass tubes filled with an indicator sorbent. The tube end is opened, the tube clipped to the firefighter, and the exposure estimated at the end of the sample period by reading a length-of-stain indicator scale. The 

exposure is then adjusted for temperature and pressure variation from the calibration 

conditions. 

A frequency distribution for all individual CO samples is shown in figure 1. The limit for 

worker exposure to CO recommended by the American Council of Government Industrial 

Hygienists (ACGIH) is 35 parts per million (ppm) by volume time-weighted over 8 hours. 

Additionally, a ceiling limit of 200 ppm is recommended. Only 3 of 49 samples were above 

35 ppm by volume. The skewed nature of the graph suggests a "log-normal" distribution, 

typical of industrial hygiene measurements. 

The time-weighted average ('rWA) CO exposures are presented in figure 2, grouped by 

work activity. Samples divided over two activities have combined designations. Firefighters 

that were lighting the burn generally had low exposures to CO. Line-holding was variable 

in firefighter CO exposure, from 0 to 14.2 ppm by volume; the exposure depended on 

whether one was upwind or downwind of the burn. Direct attack activity around small spotfires downwind of the burn produced the highest exposures. Mop-up activites did not occur 

on the sampled days. 

1 Mention of a commercial or proprietary product in this publication 

does not constitute endorsement by the U.S. Department of Agriculture of any product or service to the exclusion of others that may be 

suitable. 
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Figure 1--Carbon monoxide concentration summary: four autumn slash bums, 49 samples. 

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Figure 2--Carbon monoxide exposure by work activity for each firefighter over 1.5 to 3 hours. 
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Formaldehyde level (ppm) 

Figure 3~Formaldehyde concentration summary: four autumn slash bums. 

The frequency distribution of the formaldehyde sample concentrations is shown in figure 3. 

There are no zero values because there is a natural low parts per billion (ppb) HCHO background. A skewed trend in the frequency distribution is again evident. The ACGIH limit for 

formaldehyde is I ppm over 8 hours; a short-term limit is further recommended by the 

National Institute of Occupational Safety and Health (NIOSH), 2 ppm over any 15 minutes. 

None of the samples exceeded one-quarter of the exposure standards; as with the CO 

TWA exposures, they are grouped by work activity in figure 4. A similar trend to the CO 

data is apparent; lighting exposures were higher in intensity relative to the other work 

activities, line-holding exposures differed, and direct attack of small spot-fires was the 

highest in HCHO exposure. 

Acrolein was detected in 20 samples in the range 0 to 20 ppb. Calibration difficulties at the 

time precluded our obtaining good quantitative data, but its presence should be mentioned 

because it is a very potent irritant (ACGIH limit of 100 ppb over 8 hours). Many of the irritation effects complained of among firefighters are similar to those reported for acrolein exposure. Furfural was also detected but not quantified. 

The results of the indicator-tube passive dosimeters for CO were compared with the bag 

sample, infrared spectroscopy method over concurrent periods on the same firefighters. 

The two methods agreed, but not perfectly, as is shown in figure 5. The dosimeters were 

relatively insensitive below 6 ppm CO, were reasonable indicators of CO exposure at intermediate levels, and overpredicted CO at the two highest concentrations. A line that would 

correspond to perfect agreement is included on the graph for reference. We were not able 

to obtain good results with the dosimeters for HCHO, but the CO dosimeters performed 

fairly well. 

A correlation was found between formaldehyde and carbon monoxide, as shown in figure 

6. Twenty each of the active-method CO and HCHO samples taken concurrently on the 
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Figure 4~Formaldehyde exposure by work activity for each firefighter over 1.5 to 3 hours. 

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Parts per million carbon monoxide 

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Figure 5--Results of concurrent carbon monoxide sampling by two methods: carbon monoxide dosimeter vs. infrared spectroscopy. 
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Figure 6--Carbon monoxide vs. formaldehyde: concurrent 1.5- to 3-hour samples. 

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28 

Discussion 

firefighters were correlated with a simple linear regression; the coefficient of determination 

(r 2) was 0.865. The equation for the regression was: 

[HCHO] = [CO] * (6.038)<103) + 0.019, (1) 

where [HCHO] and [CO] are the concentrations of formaldehyde and carbon monoxide in 

ppm, respectively. The carbon monoxide is a key indicator of combustion efficiency and 

has been correlated with fine particle mass emissions from broadcast burns of conifer 

slash (Ward and Hardy 1984). 

The levels of formaldehyde and carbon monoxide at these burns were significant and had 

substantial variability. Direct attack and mop up of spot-fires produced the higher exposures, as these situations most often required firefighters to enter areas of dense smoke to 

extinguish the fires. Lighting crews had more freedom of movement to avoid smoky areas. 

A breakdown of the convection column at one burn allowed the prevailing winds to carry 

smoke across firelines and contributed to the line-holder's exposures. The higher smoke 

exposures were uncomfortable to all involved but were reported to be less than they have 

experienced at other burns and were not above ACGIH guidelines. 

At these burns, the fire managers and firefighters agreed that the smoke exposures 

seemed to be less than is often encountered. This was due to favorable winds and good 
burning technique that followed the burn plan. They also agreed that weather and fire 

behavior combine to frequently produce adverse fire situations, thereby exposing them to 

denser smoke for longer periods, which can result in health complaints. Mop-up activities 

may produce higher exposures to some air toxins, because of proximity to the source and 

the inefficient combustion conditions. We expect that more study will shed further light on 

which fire situations and activities, if any, result in exposures to air toxins that are a threat 

to firefighter safety. 

Active methods for monitoring firefighters' exposures to carbon monoxide and formaldehyde are feasible. Improvements to our methods will allow ecrolein and other aldehydes, 

respirable particulate and other important air toxins to be concurrently monitored on the 

same firefighter. An inexpensive passive dosimeter method for CO gives reasonable 

results. A similar device for formaldehyde was not satisfactory. Laboratory and field validation efforts will continue for active and passive methods. 

A linear correlation exists between carbon monoxide and formaldehyde in the smoke exposure samples collected. So far, however, the small data set renders the relation tentative. 

We will further test this correlation as exposure sampling continues in different fuel types 

and fire conditions. We hope that a dosimeter that can measure CO feasibly could additionally serve as a useful surrogate for HCHO exposure, thereby allowing widespread monitoring of the two compounds among smoke-impacted populations. 

Conclusions The preliminary data obtained from four autumn prescribed burns of mixed-conifer slash 

showed that for these broadcast burns, the convection column pulled most of the smoke 

away from the fireline and minimized firefighter smoke exposures. Exposures to carbon 

monoxide and formaldehyde were variable and may depend on work activity at the fire. 

Downwind of the burn, holding fireline and extinguishing spot-fires produced the highest 

exposure samples among the firefighters. 

Substantial progress has been made toward the development of integrative, complementary methods of monitoring different air toxins in the interference-prone fire environment. 

Passive-type, direct-reading dosimeters for CO have value as an indicator of CO exposure. 

Similar dosimeters for HCHO did not perform well but may as more experience is gained 

with them. Further tests of these devices in the fire environment could lead to their common usage by fire managers and crew bosses, who are concerned about firefighters' overexposure to smoke and desire a rapid, simple, and inexpensive exposure indicator. 

The emissions of some pollutants may be correlated. We found that carbon monoxide was 

a good predictor of formaldehyde exposure, based on our limited data. More data are 

needed to evaluate this correlation. 

Research Needs Future work will involve expansion of our efforts to determine the variability of exposures 

among firefighters in different fuel types, weather, fire behaviors, and work activities. Other 

compounds will be monitored as methods are developed. Correlations among individual 

pollutants will be tested further. 

Reports that residual smoke from prescribed burns and wildfires is trapped by topography 

and impacts down-valley residents is of concern to many. We believe that the smoke 

exposures of the firefighters may represent the upper bound exposures that rural residents 

down-valley are likely to face. We hope to test this hypothesis and evaluate correlations 

among pollutants as they are transported down-valley by monitoring at the source and at 

intermediate distances toward impacted areas. 
Acknowledgments 

Literature Cited 

Technical work was provided by Stephen Loague and Ronald Shea, We appreciate the 

cooperation of the Wenatchee National Forest. This work was supported in part by the 

State of California, Division of Forestry and Fire Protection, 

Hull, L.A. 1985. Analysis of aldehydes and ketones in the gas phase. EPA report EPAJ 

600/3-85/021. Research Triangle Park, NC: U.S. Environmental Protection Agency, 

Atmospheric Sciences Research Laboratory. 

Jackson, G.; Tietz, G.J. 1979. A preliminary analysis of employee exposure to carbon 

monoxide on wildfires and prescribed burns. Gen. Tech. Rap. [no. unknown]. Missoula, 

MT: U.S. Department of Agriculture, Forest Service, Equipment Development Center. 

Kuwata, K. 1983. Determination of aliphatic aldehydes in air by liquid chromatography. 

Analytical Chemistry. 55:2013-2015. 

Ward, Darold E.; Hardy, Colin C. 1984. Advances in the characterization and control of 

emissions from prescribed fires. Paper 84-36.3. In: Proceedings, 7Bth annual meeting of 

the Air Pollution Control Association; 1984 June 24-29; San Francisco, CA. Pittsburgh, 

PA: Air Pollution Control Association. 32 p. 

Wilson, M.L. [end others]. 1983. APTI course 435, atmospheric sampling student manual, second ed, Research Triangle Park, NC: U.S. Environmental Protection Agency, Air 

Pollution Training Institute. 
Relnhardt, Timothy E. 1991. Monitoring firefighter exposure to air toxins at 

prescribed burns of forest and range biomass. Res. Pap. PNW-RP-441. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest 

Research Station. 8 p. 

A variety of potent air toxins are in the smoke produced by burning forest and 

range biomass. Preliminary data on firefighter exposures to carbon monoxide and 

formaldehyde at four prescribed burns of Western United States natural fuels are 

presented. Formaldehyde may be correlated to carbon monoxide emissions. The 

firefighters' exposures to these compounds relative to workplace standards are 

discussed. 

Keywords: Firefighter health, air toxins, formaldehyde, carbon monoxide. 

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