U.S. Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health
Page 2 Health Hazard Evaluation Report 2012-0077-3223

Contents

Highlights...............................................i

Abbreviations ..................................... iii

Introduction......................................... 1

Background.......................................... 2

Methods ............................................... 3

Results and Discussion........................ 7

Conclusions........................................ 13

Recommendations............................. 14

Appendix A ........................................ 17

Appendix B..........................................26

References.......................................... 31

Acknowledgements........................... 35

The employer is required to post a copy of this report for 30 days at or near the 

workplace(s) of affected employees. The employer must take steps to ensure 

that the posted report is not altered, defaced, or covered by other material.

The cover photo is a close-up image of sorbent tubes, which are used by the HHE 

Program to measure airborne exposures. This photo is an artistic representation that may 

not be related to this Health Hazard Evaluation. Photo by NIOSH.
Health Hazard Evaluation Report 2012-0077-3223 Page i

We evaluated employee 

concerns about exposure 

to Libby amphibole during 

forest management activities. 

Although Libby amphibole 

was detected on some air 

samples, employee exposures 

did not exceed occupational 

exposure limits for asbestos. 

We made recommendations on 

respiratory protection, exposure 

monitoring, and personal 

protective equipment.

Highlights of this Evaluation

The Health Hazard Evaluation Program received a request from a federal forest management 

agency. Employees were concerned about exposure to Libby amphibole during forest 

management activities and wildland fire suppression in the Kootenai National Forest near a 

former vermiculite mine in Libby, Montana. We visited the federal agency station in April 

2012 and August 2012.

What We Did

● We looked at forest management and administrative work activities.

● We took personal air samples on employees for each activity they did and for the work 

shift.

● We took bulk samples of the duff (forest 

vegetation) and soil. 

● We took wipe and vacuum samples from 

equipment and bench top surfaces in the 

hydrology lab. 

● We looked at personal protective equipment 

use and talked with employees about their jobs 

and health and safety concerns. 

● We measured temperature and relative 

humidity during all activities. 

What We Found

● Employee exposures to Libby amphibole in air 

were below occupational exposure limits.

● We detected no Libby amphibole in the bulk or surface samples.

● Managers and employees were aware that Libby amphibole was present in fire 

management unit 3, but less aware about the potential for exposure or needed precautions.

● Some employees wore respirators when working in or around areas surrounding fire 

management unit 3.

● After working in fire management unit 3, employees removed and discarded equipment 

and clothing, showered, and changed into street clothing.
Page ii Health Hazard Evaluation Report 2012-0077-3223

What the Employer Can Do

● Create a respirator program for employees working in fire management unit 3.

● Start a program to periodically monitor employees’ exposure to Libby amphibole. Do 

this for forest management and fire suppression activities.

● Evaluate exposure to silica during dusty activities.

● Train employees on good work practices to minimize dust.

● Limit how often employees enter fire management unit 3.

● Schedule dust generating work (e.g., soil and duff disturbance work) when the potential 

for dust generation is low, such as when it is raining or a snow cover is present.

● Analyze samples by electron microscopy in addition to current methods. This step will 

provide better information about whether Libby amphibole fibers are present. 

What Employees Can Do

● Understand and follow all the protocols and procedures for working in fire management 

unit 3 and other areas.

● Notify your supervisor of any health or safety concerns.
Health Hazard Evaluation Report 2012-0077-3223 Page iii

Abbreviations

f/cc Fibers/cubic centimeter

CFR Code of Federal Regulations

EPA Environmental Protection Agency

NIOSH National Institute for Occupational Safety and Health

OEL Occupational exposure limit

OSHA Occupational Safety and Health Administration

FMU3 Fire management unit 3

PAPR Powered air-purifying respirator

PCM Phase contrast microscopy

PEL Permissible exposure limit

PPE Personal protective equipment

REL Recommended exposure limit

TEM Transmission electron microscopy

TWA Time-weighted average
Page iv Health Hazard Evaluation Report 2012-0077-3223

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Health Hazard Evaluation Report 2012-0077-3223 Page 1

Introduction

The Health Hazard Evaluation Program received a request from managers of a federal forest 

management agency that serves the Kootenai National Forest in Montana. The request 

concerned employees’ potential exposure to Libby amphibole during forest management and 

fire suppression activities in the area designated as fire management unit 3 (FMU3). The area 

is also known as operable unit 3 (OU3) by the United States Environmental Protection Agency 

(EPA). FMU3 surrounds a former vermiculite mine and areas impacted by the mine releases 

(Figure 1). FMU3 and other areas around the mine include approximately 32,000 acres and is 

an EPA National Priorities List Superfund site. 

Figure 1. FMU3 and mine site. Map courtesy of U.S. Forest Service.

We discussed the concerns during an initial visit in April 2012. Following an opening 

meeting with federal agency managers, employees, and EPA representatives, we obtained 

information on personal protective equipment (PPE) use, administrative controls, and 

decontamination protocols for reducing potential Libby amphibole exposure. We observed 

work practices, equipment, and vehicles used for forest management in and around FMU3. 

We also inspected the hydrology laboratory because of employee concerns about the dust 

generated when processing stream bed samples. Using this information, we developed an 

exposure assessment sampling strategy for Libby amphibole. In August 2012, we visited 

the site again to evaluate employee exposures to Libby amphibole as the employees 

worked in forest management activities. We sent interim reports with initial findings and 

recommendations to the forest managers and employee representatives in April 2012 and 

September 2012.
Page 2 Health Hazard Evaluation Report 2012-0077-3223

Background

Libby, Montana Site History

In 1881, gold miners discovered vermiculite near Libby, Montana and in the 1920s the 

Zonolite Company began mining the vermiculite. In 1963, the W.R. Grace Company 

bought the Zonolite mining operations and operated the mine until it closed in 1990. While 

in operation, the Libby mine is thought to have produced 80% of the world’s supply of 

vermiculite [EPA 2012]. In addition to vermiculite ore, asbestiform minerals, i.e., the fibrous 

minerals tremolite, winchite, and richterite, also were present. Together, these minerals are 

referred to as Libby amphibole asbestos (or Libby amphibole). 

In response to local concern and news articles about asbestos-contaminated vermiculite, the 

EPA began an investigation of Libby amphibole in November 1999. The Libby asbestos 

site, including FMU3 and other operable units in and around Libby, was added to the EPA 

National Priorities List in October 2002 and declared a public health emergency in 2009 

[EPA 2009, 2012]. This action was the first time EPA determined under the Comprehensive 

Environmental Response, Compensation, and Liability Act that conditions at a site 

constituted a public health emergency. 

High incidences of asbestos related morbidity and mortality have been documented among 

former mine and mill employees in this area [Amandus and Wheeler 1987; Amandus et al. 

1987]. Increased prevalences of asbestos related morbidity and mortality and radiographic 

pleural changes have been observed among community members and residents in this area 

[Peipins et al. 2003; Whitehouse 2004; Sullivan 2007]. In 2005, academic researchers 

determined that trees surrounding the former vermiculate mine in FMU3 were a reservoir 

for Libby amphibole [Ward et al. 2006]. This study and subsequent research indicated Libby 

amphibole was present in tree bark, forest duff, and soil [Hart et al. 2009; EPA 2011; Tetra 

Tech 2012]. In additional research, airborne asbestos fibers were detected in smoke from 

wood burning stoves and from other activities in the forested FMU3 area, such as firewood 

harvesting and wildland fire suppression tasks (e.g., fireline construction and mop-up) [Hart 

et al. 2007; Hart and Spear 2009; Hart et al. 2009; Ward et al. 2009]. The EPA has found 

Libby amphibole when conducting personal monitoring during activity-based sampling for a 

variety of activities [EPA 2011, 2013, 2014]. 

For the Libby area, the presence of Libby amphibole in FMU3 and surrounding operable 

units has not been fully characterized. No clear boundaries have been established regarding 

the extent of Libby amphibole contamination in nearby forested areas.
Health Hazard Evaluation Report 2012-0077-3223 Page 3

Canoe Gulch Ranger District

Approximately 32,000 acres within the FMU3 area are managed by the federal agency. 

The federal agency ranger district is responsible for managing federal lands inside FMU3 

and in surrounding areas. A federal agency ranger station is located just outside the FMU3 

boundary in the EPA-designated operable unit 4. Approximately 40 full-time, permanent 

federal employees are employed at the ranger station. In the summer, up to 100 additional 

seasonal employees may be hired. Work shifts are typically 8–10 hours per day. Most of 

the work done by ranger station employees involves land management activities, including 

civil engineering, trail and road maintenance, forest biology, fuels and timber management, 

hydrology, and wildland fire suppression. In winter months, the average work shifts are 

typically 8 hours, and work is done indoors and outdoors. In summer months, work shifts 

are typically 10 hours, with most work tasks being done outdoors. No research is done at the 

ranger station. 

Federal forest wildland fire suppression operations and management activities in FMU3 

have decreased since 2008–2009 when EPA declared the area a public health emergency and 

Libby amphibole contamination of tree bark, soil, and duff was identified. However, nonfire suppression activities such as trail maintenance and fuels management have occurred 

periodically in FMU3 since that time.

Methods

The purpose of our evaluation was to characterize employee dust exposures during activities 

believed to present a risk of exposure to Libby amphibole. Our evaluation included the 

following methods: (1) observing work activities and use of PPE and (2) collecting and 

analyzing the following samples for asbestos and Libby amphibole: full shift and activitybased personal air samples on employees; bulk samples of bark, duff, and soil; and wipe and 

vacuum samples from surfaces in the hydrology lab. We asked federal agency managers to 

help identify and prioritize the work activities in and around FMU3 based on the potential for 

dust generation, the number of employees involved, and the frequency and duration of the 

work. Federal agency managers were also interested in potential Libby amphibole exposures 

when employees drove in and out of the operational unit areas. We planned to evaluate 

potential Libby amphibole exposures during a prescribed wildland burn, but the burn was 

not done because of extreme fire conditions during our evaluation. The 10 work activities we 

evaluated are summarized in Table 1. These activities are typical for summer work. 
Page 4 Health Hazard Evaluation Report 2012-0077-3223

Table 1. Work activities observed and monitored during the National Institute for Occupational 

Safety and Health (NIOSH) evaluation

Activity Description

Civil engineering One employee observed road grading and brush cutting on Alexander 

Creek Road, Tamarak Creek Road, and Bear Creek Road. 

Fire cache fuel reduction

and tool maintenance

Seven employees did fuel reduction activities at the fire cache outside 

the boundary of FMU3. Sawyers operated chainsaws to cut down small 

trees and brush. Swampers hauled the brush and trees for removal. 

Employees also moved supplies in the engine garage, cleaned coolers, 

and refurbished hand tools and chainsaws. This work was done indoors 

and outdoors.

Fireline construction Seven employees constructed 0.6 miles of fireline, approximately 

30 centimeters wide, southwest of the FMU3 boundary (Figure 2). 

Employees removed combustible material to create a 1–2 meter 

firebreak by cutting and removing trees and brush with a chainsaw, then 

removing the duff and roots using specialized fire-suppression hand 

tools (combination tool, Pulaski, and McLeod hoe). 

Fuel reduction Two sawyers used chainsaws to cut brush and small trees along a 

roadway, and five swampers collected and piled the cuttings. 

Hydrology Two employees processed dry river bed samples, including weighing, 

sieving, and performing various analyses inside the lab. One employee 

collected core samples from stream beds and analyzed them in the 

hydrology lab.

Lawn care and 

maintenance

One employee mowed, weeded, and raked around the ranger station.

Office work Two employees did administrative activities inside the ranger 

station office buildings.

Road maintenance One employee raked and graded gravel and dirt roads in FMU3 and on 

other federal lands.

Timber stand 

assessment

Four employees performed timber assessments outside the boundary 

of FMU3. Employees evaluated the commercial value and health of the 

forest and determined if a fuels reduction or commercial thinning project 

was needed (Figure 3).

Trail maintenance Four employees cleared the trail of brush and logs on the Alexander trail 

inside FMU3 approximately 2 miles from the vermiculite mine (Figure 4). 
Health Hazard Evaluation Report 2012-0077-3223 Page 5

Figure 2. Fireline construction. Photo by NIOSH.

Figure 3. Timber assessment and stand exam - tree boring in Jackson Creek area, outside of FMU3. 

Photo by NIOSH.
Page 6 Health Hazard Evaluation Report 2012-0077-3223

Figure 4. Trail maintenance – sawing and swamping, Alexander Creek trail, FMU3. Photo by NIOSH.

Air, Bulk, and Surface Sampling

We collected personal air samples for asbestos and other fibers on employees during the 

activities listed in Table 1. Sampling and analysis was according to NIOSH Method 7400 

[NIOSH 2014]. We changed the sample filters as needed during the workday to prevent 

overloading and removed the filter cassettes and sampling pumps during lunch breaks and 

when employees underwent decontamination. Each employee wore two sampling devices so 

we could evaluate full shift and activity-specific exposures.

Because the field work took place in a forest environment, it was expected that the phase 

contrast microscopy (PCM) results would reveal a substantial portion of cellulose-containing 

material that met the morphological definition of a fiber. Additionally, because PCM does 

not distinguish between asbestos and non-asbestos fibers, or determine fiber mineralogy, we 

also analyzed the samples for Libby amphibole and other mineral fibers with transmission 

electron microscopy (TEM) according to NIOSH Method 7402 [NIOSH 2014]. For TEM 

analysis, we selected 27 personal air samples representing the 10 work activities and the 12 

highest fiber counts as determined by PCM.

We collected bulk samples of soil, duff, and bark for asbestos analysis with polarized light 

microscopy according to NIOSH Method 9002 [NIOSH 2014]. Polarized light microscopy 

analysis of bulk samples is reliable only when more than 1% of the material is asbestos.
Health Hazard Evaluation Report 2012-0077-3223 Page 7

We collected surface wipe samples for asbestos with pre-moistened SKC, Inc. Ghost 

Wipes. We used a 10 centimeter by 10 centimeter template to outline the sample area, 

where possible. For small or irregularly shaped surfaces we estimated the sampled area. 

We wore a new pair of gloves to take each sample. The wipe samples were analyzed with 

TEM following the American Society for Testing and Materials D 6480-05 wipe sampling 

for settled asbestos protocol [ASTM 2010]. The filters from the suspension of each sample 

used for TEM examination were also analyzed by polarized light microscopy to ensure that 

asbestos materials that may have been poorly distributed on the filter were not missed in 

TEM analysis. 

We collected surface vacuum samples in the hydrology laboratory for asbestos. These samples 

were collected by vacuuming a 10 centimeter by 10 centimeter area following American 

Society for Testing and Materials D 5755-03, with analysis by TEM [ASTM 2003].

Results and Discussion

Activities Monitored and Workplace Observations

Descriptions of the activities and number of employees monitored for each activity are 

provided in Table 2. Over the course of the evaluation, many of the same employees 

performed multiple activities. This work was done outdoors, with the exception of the time 

spent en route to the worksite in a government vehicle and returning to the ranger station, 

unless otherwise noted. Figure 5 provides a map of activity locations. All activities occurred 

within a 6.5-mile radius of the former vermiculite mine (Figure 5). Two of the activities, trail 

maintenance and fuels reduction, occurred within the FMU3 boundary (Figure 5). 

Exposure monitoring was done during the summer. There was no precipitation during our visit. 

The meteorological conditions included temperatures (in degrees Fahrenheit) from the upper 

40s (morning) to mid-90s (afternoon), percent relative humidity in the mid-teens (afternoon) 

to low-90s (morning), and wind speeds from 5–11 miles per hour. Morning dew was observed 

on vegetation during early morning activities, but no measured precipitation was reported. One 

wildland fire was reported in the region approximately 10 miles north of the FMU3 boundary, 

midway through our August visit; however, it did not interfere with our sampling.
Page 8 Health Hazard Evaluation Report 2012-0077-3223

Figure 5. NIOSH sampling locations. Map courtesy of U.S. Forest Service.
Health Hazard Evaluation Report 2012-0077-3223 Page 9

Table 2. Work activity observations and PPE use

Activity Observations and PPE use

Civil engineering The employee did not wear specific PPE. Most of the work shift was 

spent in the vehicle driving on roads in and out of FMU3. The employee 

exited the vehicle multiple times during the day for 5–40 minutes to 

check on contractor activities.

Fire cache fuel reduction

and tool maintenance

All employees wore wildland fire specific PPE (e.g., aramid fabric shirts 

and trousers [Nomex®], hardhats, hearing protection, safety glasses, 

and safety shoes). No respirators were worn. Because of extreme heat, 

employees worked on less strenuous activities in the afternoon after 

doing more strenuous work in the morning. Work occurred indoors and 

outdoors at the fire cache.

Fireline construction

(Figure 2)

Most employees wore wildland fire specific PPE, but did not wear 

respirators. Some employees did not wear safety glasses.

Fuel reduction All employees wore wildland fire specific PPE and full facepiece 

powered air purifying respirators or half-mask air purifying respirators 

with P100 particulate filters. All employees completed a three-stage wet 

decontamination process (Figure 6). The decontamination steps are 

(1) remove work clothing/gear, (2) proceed to the second stage water 

shower; and (3) proceed to the third stage to dress into street clothing.

Hydrology Surfaces in the laboratory were visibly dusty. Employees did not work 

in the laboratory at the same time. Automated screening took place in a 

room with a closed door and a fan venting to the exterior of the building. 

It was likely that suspended dust was still present in the room air at reentry. One employee wore a half-mask air purifying respirator with P100 

particulate filters.

Lawn care and 

maintenance

The employee wore a long sleeve shirt, hearing protection, safety 

glasses, hard hat, and work boots during lawn mowing and other 

outdoor activities. With the exception of maintaining equipment in a 

shed, all work was done outdoors.

Office work The majority of the work day was spent inside one or more office 

buildings, but the employees commonly walked between buildings. No 

specific PPE was worn.

Road maintenance Most work was done while driving in a government vehicle. Vehicle 

windows were open when driving. The employee periodically exited 

the vehicle to work with hand tools. The employee wore leather gloves 

and a half-mask air purifying respirator with P100 particulate filters. The 

employee used a hose to rinse the vehicle after the work shift.

Timber stand 

assessment

(Figure 3)

Teams of two employees hiked through the forest, randomly selected 

forest plots to evaluate, assessed the number and species of trees in a 

plot, measured tree height and width, bored into trees to determine age, 

and visually assessed tree health. Employees wore long sleeve shirts, 

boots, safety glasses, and hard hats.

Trail maintenance

(Figure 4)

All four employees wore wildland fire specific PPE and full facepiece 

powered air purifying respirators or half-mask respirators with P100 

particulate filters. All of the employees used the portable three-stage 

decontamination system.
Page 10 Health Hazard Evaluation Report 2012-0077-3223

Figure 6. Portable three-stage decontamination. Photo by NIOSH.

Personal Breathing Zone Sample Results

Tables A1–A8 (Appendix A) present individual full-shift and shorter-term activity-based 

personal air sample results by activity as determined by PCM analysis. Six out of 109 air 

samples analyzed by PCM exceeded the NIOSH recommended exposure limit (REL) and 

Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) of 

0.1 fibers/cubic centimeter (f/cc), as an 8-hour time-weighted average (TWA) (See Appendix 

B for occupational exposure limits for asbestos and other fibers). These samples were all 

collected during the fireline construction activities (Table A4). An additional four samples 

from fireline construction had concentrations of 0.05–0.1 f/cc by PCM analysis. To determine 

if fibers detected by PCM were Libby amphibole, TEM analyses were performed on 27 

samples. These samples included the 12 samples with the highest f/cc results by PCM and 15 

samples chosen to represent all activities during the week. 

Table A9 presents the calculated concentration based on PCM results for samples presented 

for TEM analysis together with the number and type of mineral fibers observed in 80 grid 

openings for each sample. Due to the low number of mineral fibers found, no attempt was 

made to adjust the PCM counts. Of the 27 samples evaluated, six contained mineral fibers, 

five contained richterite (one of the fibers that compose Libby amphibole), and one contained 

chrysotile (a serpentine form of asbestos). Of the five samples containing richterite, four were 

collected during fireline construction activities and one was collected during fuel reduction 

activities. The sample containing chrysotile was collected in the hydrology laboratory 

and was likely derived from sources other than the vermiculite mine. Chrysotile is a nonamphibole form of asbestos and is neither associated with the Libby mine nor present in 

Libby amphibole. The TEM results provide evidence that most fibers detected by PCM were 

not asbestos but were other fibers (e.g., cellulose-containing) that met the morphological fiber 

criteria defined in the PCM method.
Health Hazard Evaluation Report 2012-0077-3223 Page 11

On the basis of these results, we did not find that employee exposures to Libby amphibole 

exceeded occupational exposure limits (OELs) during various forest management activities in 

and around FMU3. Even though none of the exposures were above OELs, these results, may not 

be representative of potential exposures in other areas in or around FMU3, nor should they be 

extrapolated to wildland firefighting activities (wildland fire or prescribed burn). In addition, all 

activities where Libby amphibole fibers were identified were outside FMU3 with one exception 

(sawyer, Alexander Peak trail). This finding indicates employees working in areas outside of 

FMU3 may be exposed to Libby amphibole. Four of the five air samples containing Libby 

amphibole were collected during the dusty activity of fireline construction. Thus, appropriate 

precautions to protect employees during these types of activities should be implemented. 

No asbestos fibers, including Libby amphibole, were detected on any of the surface wipe or 

surface vacuum samples collected in the hydrology laboratory. No asbestos fibers, including 

Libby amphibole, were detected in any of the bulk samples collected in the hydrology 

laboratory or when employees were doing forest management activities. 

Our evaluation found non-asbestos material that met the definition of a fiber on samples 

analyzed by PCM. Because PCM is incapable of distinguishing between asbestos and nonasbestos fibers, erroneous conclusions could be drawn without this confirmatory analysis.

Occupational Safety and Health Programs

Wildland Fire Suppression

The federal agency had written health and safety programs and protocols for wildland 

fire suppression and response activities in FMU3 including a wildfire response guide and 

fire suppression job hazard analysis. Fire suppression protocols were designed to limit 

firefighters’ exposure to Libby amphibole by first relying on aviation resources (e.g., water 

and retardant dropped from helicopters and air-tankers) to suppress the fire. If ground based 

firefighting personnel were necessary to supplement aviation resources, the agency identified 

and trained 15 non-seasonal employees who volunteered for wildfire suppression activities in 

this area. Mitigation measures for firefighters were identified and included avoiding smoke, 

minimizing the disturbance of duff, and minimizing use of chainsaws. 

When working inside the FMU3 boundaries, the wildfire response guide indicates that 

federal agency personnel are required to wear a powered air purifying respirator (PAPR) 

and go through decontamination when doing suppression activities on the fireline or when 

exposed to smoke. Federal agency employees located outside of the FMU3 boundary, but 

who are supporting fire suppression activities in FMU3, have been approved to use half-mask 

respirators provided they are fit tested and complete an on-line medical screening form and 

the forest respiratory training program [Bradford 2012]. The job hazard analysis describes 

in detail the required wildland fire specific PPE, which includes the use of a PAPR, the PPE 

donning and doffing requirements, and decontamination of personnel and clothing. Since the 

wildland fire suppression guidelines were implemented, the one fire that required a response 

from the federal agency only required aviation resources for suppression. 
Page 12 Health Hazard Evaluation Report 2012-0077-3223

Prior to any assignment associated with fire suppression in FMU3, firefighters must have a 

medical screening exam; be trained, medically cleared, and fit tested for a PAPR; complete 

a review of the respiratory protection plan, the job hazard analysis, and wildfire response 

guide; and complete a fire suppression drill and equipment checklist. In 2011, a medical 

monitoring program was implemented for the 15 employees who would conduct fire 

suppression activities in FMU3. It consists of a baseline medical examination as described in 

the OSHA asbestos standard, 29 CFR 1910.1001(l) Medical Surveillance. 

The wildfire response guide indicates that ambient air sampling would be conducted during 

a wildfire to characterize the potential exposure to Libby amphibole from smoke. Because 

of the potential for ground disturbing activities and exposure to smoke, the federal agency 

should develop an exposure assessment strategy for firefighting personnel during wildland 

fires and prescribed burns. As wildland fires are unpredictable, considerable pre-planning is 

needed to ensure adequate preparation for sampling in the event of a fire.

Forest Management Activities

Since 2008, forest management activities (e.g., road and trail maintenance) have been 

significantly restricted in FMU3. The federal agency had no written protocols for nonwildland fire activities in FMU3; however, a supervisor reviews and approves all proposed 

activities in this area on the basis of need, duration, and time of year. The federal agency 

attempts to schedule work in FMU3 during environmental conditions that minimize dust 

exposures (e.g., when it is raining, or there is at least a 6-inch snow cover). Supervisors 

review activities and conditions in FMU3 and make recommendations on entry requirements, 

PPE, and work protocols/practices.

Although there was no written program for non-wildland fire activities, federal agency 

managers indicated they had a respiratory protection program and decontamination protocols 

for all work inside FMU3. Full facepiece PAPRs or half-mask air purifying respirators with 

P100 filters were required. All personnel we monitored in FMU3 wore respiratory protection. 

It was our understanding that the federal agency would use results from our evaluation 

to update and modify the respiratory protection program as appropriate. Given that our 

evaluation occurred over a limited period of time, additional monitoring under different 

conditions and activities is recommended to assist in determining whether respirator use 

should remain as currently defined, be changed (i.e., downgrade or upgrade the level of 

protection), or be discontinued. Additionally, although characterizing silica exposures was 

not part of this evaluation, the federal agency should evaluate silica exposures during those 

forest management activities having the potential to create a dusty environment, such as 

fireline construction. Ultimately, reducing dust exposures and limiting work in and around 

FMU3 is a reasonable risk-based strategy to reduce potential occupational exposures to 

Libby amphibole and silica.

All employees doing forest management activities in FMU3 were required to undergo 

decontamination upon completion of work and dispose of used equipment and PPE. The 

ranger station obtained a three-stage mobile decontamination unit (described in Table 2 

and shown in Figure 6) and trained employees on how to deploy and use this unit. Only 
Health Hazard Evaluation Report 2012-0077-3223 Page 13

federal agency vehicles are used for work inside FMU3. During our visit the only vehicle 

we observed being washed was the road maintenance vehicle after the work shift. Washing 

the vehicles after traveling in FMU3 or on dusty roads would help in removing potential 

asbestos-containing dust and decrease the potential for secondary exposure. Frequent 

cleaning of the vehicle interior with a vacuum equipped with a high efficiency particulate air 

filter will also help decrease secondary exposures.

Wildland fire fighters are at increased risk of heat-related illness because of the metabolic 

work requirements of the job, the hot environmental conditions they work in, and the 

potential for long work hours. The use of additional PPE (e.g., respirators) to reduce potential 

exposures to Libby amphibole may create an additional physiological burden on the worker 

and may increase the likelihood of heat-related illness, especially during summer months.

Conclusions

Although Libby amphibole was found in some personal air samples, all concentrations 

we measured during various forest management activities in areas surrounding the former 

vermiculite mine were below OELs. No asbestos was identified in any of the bulk or 

surface samples we collected. Although our evaluation identified no overexposures to Libby 

amphibole, reducing dust generation and limiting the number of employees doing dustgenerating activities is recommended.
Page 14 Health Hazard Evaluation Report 2012-0077-3223

Recommendations

On the basis of our findings, we recommend the actions listed below. We encourage the 

federal agency at the ranger station to use a labor-management health and safety committee 

or working group to discuss our recommendations and develop an action plan. Those 

involved in the work can best set priorities and assess the feasibility of our recommendations 

for the specific situation at the ranger station. 

These recommendations apply to all activities in all areas where forest management activities 

occur, and are good work practices that should be followed whenever dust exposure can 

occur, regardless of the presence or absence of Libby amphibole. These recommendations are 

consistent with the Agency for Toxic Substances and Disease Registry recommendations for 

employees in areas where asbestos may be present.

Our recommendations are based on an approach known as the hierarchy of controls 

(Appendix B). This approach groups actions by their likely effectiveness in reducing or 

removing hazards. In most cases, the preferred approach is to eliminate hazardous materials 

or processes and install engineering controls to reduce exposure or shield employees. Until 

such controls are in place, or if they are not effective or feasible, administrative measures and 

PPE may be needed. 

Administrative Controls

The term administrative controls refers to employer-dictated work practices and policies 

to reduce or prevent hazardous exposures. Their effectiveness depends on employer 

commitment and employee acceptance. Regular monitoring and reinforcement are necessary 

to ensure that policies and procedures are followed consistently.

Minimizing Dust Exposures

1. Limit how often employees enter FMU3.

2. Schedule dust generating activities (e.g. soil and duff disturbance work) when the 

potential for dust generation is low (rain/wet conditions, snow).

3. Use wet methods, where possible, to reduce dust generation. As is commonly done at 

construction and other outdoor work sites, use water trucks for dust suppression.

4. Wet wash equipment and vehicle exteriors at the end of the day/shift, and clean vehicle 

interiors frequently using a vacuum equipped with a high efficiency particulate air 

filter and wet wiping methods.

5. Ensure employees are informed of the need to use dust control methods during any 

work and that they are trained on dust control techniques. Inform contractors about 

potential exposures to Libby amphibole and procedures for reducing dust generation.

6. Prohibit dry sweeping, the use of leaf blowers, and the use of compressed air for 

cleaning clothing or other dusty materials and equipment.

7. Train ranger station employees about the hazards of Libby amphibole, areas where 
Health Hazard Evaluation Report 2012-0077-3223 Page 15

Libby amphibole contamination is known or suspected, what is known and not 

known about exposure and health effects, actions to reduce their potential for 

exposure, scheduling work in FMU3, PPE use, and cleaning and decontamination, at a 

minimum. Update employees as new information is received. 

8. Establish protocols for vehicle use on dirt/gravel roads (e.g., drive slowly, have vents 

closed, and keep windows closed).

9. Instruct employees to change into clean clothing before leaving the worksite or 

returning to their residence when they have been working in dusty areas. Work 

clothing should be cleaned according to the requirements of the OSHA asbestos 

standard, 29 CFR 1910.1001.

10.Instruct employees to move away from dusty work areas for breaks and wash their 

hands and face before eating, drinking, or smoking. Ensure that employees have clean 

water for this purpose.

11.Limit bystander exposure by preventing visitors and coworkers from standing in work 

areas where dust is generated. 

Monitoring

1. Establish a program to periodically monitor exposure to Libby amphibole among 

federal agency employees. This program should include evaluating activities in and 

around FMU3 and during different climatic conditions. Further characterization of 

work activities, especially those that create dust, will provide additional data and help 

inform decisions about work practices and PPE. 

2. Use TEM per NIOSH Method 7402 for all analyses to augment and confirm the results 

of any samples analyzed using the traditional PCM method, NIOSH Method 7400. 

3. Characterize firefighter exposure to Libby amphibole during fire suppression activities 

(wildland fires and prescribed burns). As wildland fires are unpredictable, considerable 

pre-planning is needed to ensure adequate preparation for sampling in the event of a fire. 

4. Evaluate employee exposure to silica during forest management activities that 

generate dust. 

Personal Protective Equipment

PPE is the least effective means for controlling hazardous exposures. Proper use of 

PPE requires a comprehensive program and a high level of employee involvement and 

commitment. The right PPE must be chosen for each hazard. Supporting programs such as 

training, change-out schedules, and medical assessment may be needed. PPE should not 

be the sole method for controlling hazardous exposures. Rather, PPE should be used until 

effective engineering and administrative controls are in place.

1. Develop a written respiratory protection program to identify the job activities, type of 

respirator, and locations where respirator use is required. Respiratory hazards should 

be evaluated for job activities where respiratory protection is currently required to 
Page 16 Health Hazard Evaluation Report 2012-0077-3223

ensure that the respirators being used are necessary and appropriate. 

a. If respirators are deemed necessary, the respiratory protection program must 

identify the type of respirator required for those activities. 

b. Ensure that all requirements in the OSHA respiratory protection standard [29 

CFR 1910.134] are met (e.g., training, fit testing, medical clearance, respirator 

cleaning and storage).

2. Provide a copy of Appendix D of the OSHA respiratory protection standard [29 CFR 

1910.134] to employees to meet the OSHA requirements for voluntary respirator use, 

if the federal agency allows voluntary respirator use (after a determination is made that 

respiratory protection is not required).

a. Ensure that any employee using a respirator of higher protection than a 

filtering facepiece respirator is medically fit to use that respirator, and that the 

respirator is cleaned, stored, and maintained so that its use does not present a 

health hazard to the user. 

b. Job activities where employees voluntarily wear respirators should be noted in 

the written respiratory protection program. 

c. Encourage employees who voluntarily wear respirators to follow all aspects 

of proper respirator use including being clean shaven when using the 

respirator to ensure a good seal.

3. Consider how additional PPE may increase the physiological burden on the worker in 

this environment. Heat-related illness recommendations for wildland fire fighters can 

be found at http://www.fs.fed.us/eng/pubs/pdfpubs/pdf10512316/pdf10512316dpi300.

pdf and http://www.cdc.gov/niosh/fire/reports/face201117.html. 
Health Hazard Evaluation Report 2012-0077-3223 Page 17

Appendix A: Tables

Table A1. Personal air samples collected during sawing and clearing activities at the Alexander 

trail Head on August 13, 2012, and analyzed for asbestos with phase contrast microscopy 

Job/Activity Sample

number

Sample

time

(military)

Sample

volume

(liters)

Sample

concentration

(f/cc)

Full shift

TWA

(f/cc)*

Full shift sampling†

Swamper 1 135 0958–1701¶ 792 — 0.037

Swamper 2 144 1000–1700¶ 777 — 0.027

Swamper 3 129 1008–1659¶ 740 — 0.021

Swamper 4 123 1009–1700¶ 729 — 0.043

Sawyer 1 86

137

0835–1236

1312–1647¶

471

420

0.044

0.037

0.041

Sawyer 2 122

88

0821–1236

1338–1631¶

506

341

0.046

0.015

0.033

Activity-specific sampling§

Swamper 1 134‡ 1130–1528 724 0.048 —

Swamper 2 131 1132–1527 714 0.035 —

Swamper 3 138 1118–1528 756 0.035 —

Swamper 4 132 1119–1520 736 0.037 —

Sawyer 1 145‡ 0914–1234 690 0.084 —

Sawyer 2 127‡ 0928–1236 566 0.075 —

*The NIOSH REL and OSHA PEL for asbestos, including Libby amphibole, is 0.1 f/cc

†Full shift sampling, includes driving time, activities conducted, other ancillary (e.g., office) work

‡Sample also analyzed by TEM (Table A9) 

§Activity-specific sampling for the activity as described in Tables 1 and 2

¶Employee went through decontamination; pump removed for approximately 20 minutes
Page 18 Health Hazard Evaluation Report 2012-0077-3223

Table A2. Personal air samples collected during sawing and clearing activities at the fire cache on 

August 16, 2012, and analyzed for asbestos with phase contrast microscopy 

Job/Activity Sample

number

Sample

time

(military)

Sample

volume

(liters)

Sample

concentration

(f/cc)

Full shift

TWA

(f/cc)*

Full-shift sampling†

Swamper 1 82

157

0813–1247

1343–1603

507

421

0.031

0.018

0.026

Swamper 2 92

156

0814–1245

1341–1601

530

424

0.0068

0.020

0.011

Swamper 3 1

142

0817–1249

1345–1602

529

404

0.021

0.016

0.019

Sawyer 1 80

158

0804–1250

1347–1603

551

409

0.0087

0.021

0.013

Sawyer 2 72

161

0810–1248

1346–1603

534

418

0.011

0.0075

0.010

Sawyer 3 146

160

0809–1248

1344–1602

552

421

0.011

0.018

0.013

Sawyer 4 136

159

0810–1246

1342–1602

550

275

0.019

0.024

0.021

Activity-specific sampling§

Swamper 1 43

157

0940–1247

1343–1603

562

421

0.018

0.018

—

Swamper 2 65

156

0936–1245

1341–1601

572

424

0.010

0.020

—

Swamper 3 17‡

142

0938–1249

1345–1602

563

404

0.013

0.016

—

Sawyer 1 103‡

15

0934–1250

1347–1603

589

409

0.018

0.021

—

Sawyer 2 113

161

0933–1248

1346–1603

595

418

0.013

0.0075

—

Sawyer 3 91

160

0932–1248

1344–1602

598

421

0.014

0.018

—

Sawyer 4 119

159

0930–1246

1342–1602

595

275

0.013

0.024

—

*The NIOSH REL and OSHA PEL for asbestos, including Libby amphibole, is 0.1 f/cc

†Full-shift sampling, includes driving time, activities conducted, other ancillary (e.g., office) work

‡Sample also analyzed by TEM (Table A9) 

§Activity-specific sampling for the activity as listed in Tables 1 and 2
Health Hazard Evaluation Report 2012-0077-3223 Page 19

Table A3. Personal air samples collected during sample analysis activities in the hydrology 

laboratory and analyzed for asbestos with phase contrast microscopy

Job/Activity Sample

number

Sample

time

(military)

Sample

volume

(liters)

Sample

concentration

(f/cc)

Full shift

TWA

(f/cc)*

Full-shift sampling†

Laboratorian 1 –

8/13/13

126‡ 0723–1153 536 0.010¶ —

Laboratorian 2 –

8/16/13

41

33

63

0746–0911

0911–1010

1010–1722

168

116

852

0.033

0.025

Overloaded

—

Activity-specific sampling§

Laboratorian 1 –

8/13/13

110 0755–1152 720 0.007 —

Laboratorian 2 –

8/16/13

20

58

50‡

0746–0912

0912–1010

1010–1204

262

177

347

0.027

0.035

0.017

—

NIOSH observer 25 0840–0916 72 0.031 —

*The NIOSH REL and OSHA PEL for asbestos, including Libby amphibole, is 0.1 f/cc

†Full-shift sampling includes driving time, activities conducted, other ancillary (e.g., office) work

‡Sample also analyzed by TEM (Table A9) 

§Activity-specific sampling for the activity as listed in Tables 1 and 2

¶Employee left the hydrology laboratory after lunch. Full-shift sampling was not done.
Page 20 Health Hazard Evaluation Report 2012-0077-3223

Table A4. Personal air samples collected during fireline construction activities on August 14, 

2012, and analyzed for asbestos with phase contrast microscopy 

Job/Activity Sample

number

Sample

time

(military)

Sample

volume

(liters)

Sample

concentration

(f/cc)

Full shift

TWA

(f/cc)*

Full-shift sampling†

Employee 1 61‡

133

0810–1207

1248–1649

474

729

0.13

0.0082

0.069

Employee 2 45‡

105

0810–1205

1249–1647

468

728

0.094

0.0069

0.050

Employee 3 81

117

0825–1205

1250–1646

424

728

0.026

0.0089

0.017

Employee 4 68‡

107

0829–1207

1251–1646

415

722

0.051

0.013

0.031

Employee 5 89‡

101

0825–1208

1252–1647

432

707

0.10

0.013

0.055

Employee 6 24‡

116

0829–1206

1253–1648

413

712

0.11

0.0053

0.056

Employee 7 39‡

102

0839–1205

1253–1648

398

712

0.16

0.0088

0.079

Activity-specific sampling§

Employee 1 125‡

133

0918–1207

1248–1649

511

729

0.17

0.0082

—

Employee 2 27

105

0925–1205

1249–1647

489

728

Overloaded

0.0069

—

Employee 3 30

117

925–1204

1250–1646

491

728

0.026

0.089

—

Employee 4 51‡

107

0931–1207

1251–1646

480

722

0.058

0.013

—

Employee 5 74‡

101

0929–1208

1252–1647

478

707

0.081

0.013

—

Employee 6 77

116

0930–1206

1253–1648

479

712

Overloaded

0.0053

—

Employee 7 78‡

102

0928–1203

1253–1648

469

712

0.14

0.0088

—

NIOSH Observer 94 1003–1218 412 0.033 —

*The NIOSH REL and OSHA PEL for asbestos, including Libby amphibole, is 0.1 f/cc

†Full-shift sampling, includes driving time, activities conducted, other ancillary (e.g., office) work

‡Sample also analyzed by TEM (Table A9) 

§Activity-specific sampling for the activity as listed in Tables 1 and 2
Health Hazard Evaluation Report 2012-0077-3223 Page 21

Table A5. Personal air samples collected during various activities at the ranger station on August 

14, 2012, and analyzed for asbestos with phase contrast microscopy 

Job/Activity Sample

number

Sample

time

(military)

Sample

volume

(liters)

Sample

concentration

(f/cc)

Full shift

TWA

(f/cc)*

Full-shift sampling†

Office employee,

technical services

building

76 0733–1545 958 0.016 0.016

Maintenance, facilities

and lawn care

143

66

0737–0956

0956–1103

279

134

0.022

0.036

0.027

Office employee, 

main building

139 0745–1147¶

1317–1612

817 0.007 0.007

Activity-specific sampling§

Office employee,

technical services

building

54 0733–1545 1500 0.009 —

Maintenance, facilities

and lawn care

118

97

0737–0956

0956–1103

421

203

0.015

0.025

—

Office employee, 

main building

69 0745–1612 1543 0.004 —

*The NIOSH REL and OSHA PEL for asbestos, including Libby amphibole, is 0.1 f/cc

†Full-shift sampling, includes driving time, activities conducted, other ancillary (e.g., office) work

‡Sample also analyzed by TEM (Table A9) 

§Activity-specific sampling for the activity as listed in Tables 1 and 2

¶Pump fault at 1147. Missing approximately 1.5 hours.
Page 22 Health Hazard Evaluation Report 2012-0077-3223

Table A6. Personal air samples collected during trail maintenance activities on the Alexander 

Peak trail on August 14, 2012, and analyzed for asbestos with phase contrast microscopy 

Job/Activity Sample

number

Sample

time

(military)

Sample

volume

(liters)

Sample

concentration

(f/cc)

Full shift

TWA

(f/cc)*

Full-shift sampling†

Swamper 1 140

9

0739–1244

1244–1659¶

601

473

0.0092

0.012

0.010

Sawyer 1 2

15

0737–1243

1243–1608¶

607

371

0.0071

0.012

0.009

Swamper 2 6

40

0738–1246

1246–1659¶

596

364

0.019

0.011

0.016

Sawyer 2 104

52

0739–1241

1241–1609¶

598

343

0.017

0.031

0.022

Activity-specific sampling§

Swamper 1 121

26

0940–1244

1244–1524

561

488

0.013

0.014

—

Sawyer 1 128

49

0940–1243

1243–1525

553

490

0.014

0.011

—

Swamper 2 148‡

16

0940–1246

1246–1525

563

481

0.016

0.014

—

Sawyer 2 34‡

31‡

0920–1241

1241–1521

610

485

0.019

0.027

—

*The NIOSH REL and OSHA PEL for asbestos, including Libby amphibole, is 0.1 f/cc

†Full-shift sampling, includes driving time, activities conducted, other ancillary (e.g., office) work

‡Sample also analyzed by TEM (Table A9) 

§Activity-specific sampling for the activity as listed in Tables 1 and 2

¶Employee went through decontamination; pump removed for approximately 20 minutes
Health Hazard Evaluation Report 2012-0077-3223 Page 23

Table A7. Personal air samples collected during timber stand assessments in Jackson Creek and 

South Fork Junction on August 15, 2012, and analyzed for asbestos with phase contrast microscopy 

Job/Activity Sample

number

Sample time

(military)

Sample

volume

(liters)

Sample

concentration

(f/cc)

Full shift

TWA

(f/cc)*

Full-shift sampling†

Timber supervisor 37 0800–1542 885 0.098 0.098

Sr. fire fighter 112 0801–1541 888 0.018 0.018

Forestry technician 1 100

79

0803–1340

1341–1706

659

400

0.015

0.019

0.017

Forestry technician 2 62‡

95‡

0843–1342

1342–1707

585

396

0.025

0.033

0.028

NIOSH observer 18

83

0810–1343

1344–1708

662

406

0.015

0.010

0.013

Activity-specific sampling§

Timber supervisor¶ 38‡ 0844–1118 476 0.026 —

Sr. fire fighter 32

73

0845–1117

1212–1454

458

488

0.0089

0.011

—

Forestry technician 1 21

109

0845–1117

1223–1627

467

749

0.023

0.014

—

Forestry technician 2 84‡

106‡

0845–1117

1221–1625

470

754

0.026

0.017

—

NIOSH observer 35 0847–1118

1227–1628

1196 0.0064 —

*The NIOSH REL and OSHA PEL for asbestos, including Libby amphibole, is 0.1 f/cc

†Full-shift sampling, includes driving time, activities conducted, other ancillary (e.g., office) work

‡Sample also analyzed by TEM (Table A9) 

§Activity-specific sampling for the activity as listed in Tables 1 and 2

¶Air sample collected on this employee in the afternoon was lost. Morning sample result is 

provided.
Page 24 Health Hazard Evaluation Report 2012-0077-3223

Table A8. Personal air samples collected during other activities on August 15 and 16, 2012, and 

analyzed for asbestos with phase contrast microscopy 

Job/Activity Sample

number

Sample

time

(military)

Sample

volume

(liters)

Sample

concentration

(f/cc)

Full shift

TWA

(f/cc)*

Full-shift sampling†

Civil engineering technician,

observe road grading and brush

cutting on Alexander Creek Road,

Tamarak Creek Road, and Bear

Creek Road – August 15, 2012

70‡ 0800–1536 889 0.023 0.023

Road raking and maintenance – 

August 16, 2012

93 0742–1552 955 0.021 0.021

Activity-specific sampling§

Road raking and maintenance 48‡ 0927–1420 898 0.011 —

*The NIOSH REL and OSHA PEL for asbestos, including Libby amphibole, is 0.1 f/cc

†Full-shift sampling, includes driving time, activities conducted, other ancillary (e.g., office) work

‡Sample also analyzed by TEM (Table A9) 

§Activity-specific sampling for the activity as listed in Tables 1 and 2
Health Hazard Evaluation Report 2012-0077-3223 Page 25

Table A9. Personal air samples analyzed for asbestos using transmission electron microscopy

Job/Activity Sample

number

PCM concentration

(f/cc)

Number and type of

fiber detected by TEM*

Fuel reduction at the Alexander trail

Swamper 1 134 0.048 0

Sawyer 1 145 0.084 0

Sawyer 2 127 0.075 0

Trail maintenance on Alexander trail

Swamper 2 148 0.016 0

Sawyer 2 34 0.019 2 (richterite)

Sawyer 2 31 0.027 0

Fire cache fuel reduction and cleanup

Sawyer 1 103 0.018 0

Swamper 3 17 0.013 1 (richterite)

Hydrology 

Laboratorian 1 126 0.010 0

Laboratorian 2 50 0.017 1 (chrysotile)

Fireline construction

Employee 1 61 0.13 1.5 (richterite)

Employee 1 125 0.17 0

Employee 2 45 0.094 1 (richterite)

Employee 4 68 0.051 1 (richterite)

Employee 4 51 0.058 0

Employee 5 89 0.10 0

Employee 5 74 0.081 0

Employee 6 24 0.11 0

Employee 7 39 0.16 0

Employee 7 78 0.14 0

Timber stand assessment

Timber supervisor 38 0.026 0

Forestry technician 2 62 0.025 0

Forestry technician 2 95 0.033 0

Forestry technician 2 84 0.026 0

Forestry technician 2 106 0.017 0

Other job/activities

Civil engineering technician 70 0.023 0

Road maintenance 48 0.011 0

*The number and type of mineral fibers, including asbestos, confirmed by TEM on that sample
Page 26 Health Hazard Evaluation Report 2012-0077-3223

Appendix B: Occupational Exposure Limits and 

Health Effects

NIOSH investigators refer to mandatory (legally enforceable) and recommended OELs for 

chemical, physical, and biological agents when evaluating workplace hazards. OELs have 

been developed by federal agencies and safety and health organizations to prevent adverse 

health effects from workplace exposures. Generally, OELs suggest levels of exposure that 

most employees may be exposed to for up to 10 hours per day, 40 hours per week, for a 

working lifetime, without experiencing adverse health effects. However, not all employees 

will be protected if their exposures are maintained below these levels. Some may have 

adverse health effects because of individual susceptibility, a pre-existing medical condition, 

or a hypersensitivity (allergy). In addition, some hazardous substances act in combination 

with other exposures, with the general environment, or with medications or personal habits of 

the employee to produce adverse health effects. Most OELs address airborne exposures, but 

some substances can be absorbed directly through the skin and mucous membranes.

Most OELs are expressed as a TWA exposure. A TWA refers to the average exposure during 

a normal 8- to 10-hour workday. Some chemical substances and physical agents have 

recommended short-term exposure limit or ceiling values. Unless otherwise noted, the shortterm exposure limit is a 15-minute TWA exposure. It should not be exceeded at any time 

during a workday. The ceiling limit should not be exceeded at any time.

In the United States, OELs have been established by federal agencies, professional 

organizations, state and local governments, and other entities. Some OELs are legally 

enforceable limits; others are recommendations. 

● The U.S. Department of Labor OSHA PELs (29 CFR 1910 [general industry]; 29 CFR 

1926 [construction industry]; and 29 CFR 1917 [maritime industry]) are legal limits. 

These limits are enforceable in workplaces covered under the Occupational Safety and 

Health Act of 1970. 

● NIOSH RELs are recommendations based on a critical review of the scientific and 

technical information and the adequacy of methods to identify and control the hazard. 

NIOSH RELs are published in the NIOSH Pocket Guide to Chemical Hazards [NIOSH 

2010]. NIOSH also recommends risk management practices (e.g., engineering controls, 

safe work practices, employee education/training, PPE, and exposure and medical 

monitoring) to minimize the risk of exposure and adverse health effects.

● Other OELs commonly used and cited in the United States include the threshold 

limit values (TLVs), which are recommended by the American Conference of 

Governmental Industrial Hygienists, a professional organization, and the workplace 

environmental exposure levels, which are recommended by the American Industrial 

Hygiene Association, another professional organization. The threshold limit values and 

workplace environmental exposure levels are developed by committee members of 

these associations from a review of the published, peer-reviewed literature. These OELs 

are not consensus standards. Threshold limit values are considered voluntary exposure 
Health Hazard Evaluation Report 2012-0077-3223 Page 27

guidelines for use by industrial hygienists and others trained in this discipline “to assist 

in the control of health hazards” [ACGIH 2014]. Workplace environmental exposure 

levels have been established for some chemicals “when no other legal or authoritative 

limits exist” [AIHA 2014].

Outside the United States, OELs have been established by various agencies and organizations 

and include legal and recommended limits. The Institut für Arbeitsschutz der Deutschen 

Gesetzlichen Unfallversicherung (Institute for Occupational Safety and Health of the German 

Social Accident Insurance) maintains a database of international OELs from European 

Union member states, Canada (Québec), Japan, Switzerland, and the United States. The 

database, available at http://www.dguv.de/ifa/Gefahrstoffdatenbanken/GESTIS-InternationaleGrenzwerte-für-chemische-Substanzen-limit-values-for-chemical-agents/index-2.jsp, contains 

international limits for more than 1,500 hazardous substances and is updated periodically. 

OSHA requires an employer to furnish employees a place of employment free from 

recognized hazards that cause or are likely to cause death or serious physical harm 

[Occupational Safety and Health Act of 1970 (Public Law 91–596, sec. 5(a)(1))]. This is 

true in the absence of a specific OEL. It also is important to keep in mind that OELs may not 

reflect current health-based information.

When multiple OELs exist for a substance or agent, NIOSH investigators generally 

encourage employers to use the lowest OEL when making risk assessment and risk 

management decisions. NIOSH investigators also encourage use of the hierarchy of controls 

approach to eliminate or minimize workplace hazards. This includes, in order of preference, 

the use of (1) substitution or elimination of the hazardous agent, (2) engineering controls 

(e.g., local exhaust ventilation, process enclosure, dilution ventilation), (3) administrative 

controls (e.g., limiting time of exposure, employee training, work practice changes, medical 

surveillance), and (4) PPE (e.g., respiratory protection, gloves, eye protection, hearing 

protection). Control banding, a qualitative risk assessment and risk management tool, is a 

complementary approach to protecting employee health. Control banding focuses on how 

broad categories of risk should be managed. Information on control banding is available at 

http://www.cdc.gov/niosh/topics/ctrlbanding/. This approach can be applied in situations 

where OELs have not been established or can be used to supplement existing OELs.

Asbestos

Asbestos is a commercial name, not a mineralogical definition, given to a group of six 

different fibrous minerals (amosite, chrysotile, crocidolite, and the fibrous varieties of 

tremolite, actinolite, and anthophyllite) that occur naturally in the environment. One of these, 

chrysotile, belongs to the serpentine family of minerals, while all of the others belong to 

the amphibole family. These minerals possess high tensile strength, flexibility, resistance to 

chemical, biological, and thermal degradation, and electrical resistance. Because of these 

properties, asbestos has been mined for use in a wide range of manufactured products, mostly 

in building materials, friction products, and heat-resistant fabrics. Chrysotile, also known as 

white asbestos, is the predominant commercial form of asbestos; amphiboles are considered 

of minor commercial importance. Historically, chrysotile accounted for more than 90% of 
Page 28 Health Hazard Evaluation Report 2012-0077-3223

the world’s mined asbestos; it presently accounts for over 99% [Ross and Virta 2001; USGS 

2008]. Chrysotile asbestos has been used in a number of applications in the United States, 

including thermal piping and industrial oven insulation, floor tile, vehicle brake pads, and in 

building material such as soffits. More information about asbestos is available at the NIOSH 

asbestos topic page http://www.cdc.gov/niosh/topics/asbestos/.

The current OSHA occupational 8-hour TWA exposure limit for airborne asbestos, including 

Libby amphibole, as determined by PCM is 0.1 f/cc for fibers greater than 5 micrometers in 

length and an aspect ratio (length to width) greater than or equal to 3:1 [29 CFR 1910.1001]. 

OSHA has also established an excursion limit that requires the employer to ensure that 

no employee is exposed to an airborne concentration of asbestos in excess of 1.0 f/cc as 

averaged over a sampling period of 30 minutes. Exposure limits or risk criteria for bulk or 

surface samples for asbestos have not been established. OSHA’s definition of asbestos applies 

to chrysotile, amosite, crocidolite, tremolite asbestos, anthophyllite asbestos, actinolite 

asbestos, and any of these minerals that have been chemically treated and/or altered [29 CFR 

1910.1001]. The OSHA definition of asbestos-containing material is any material containing 

more than 1% asbestos.

In 1990, NIOSH reviewed the available information on elongate mineral particles and 

concerns about potential health risks associated with employee exposures to the analogs of 

the asbestos minerals [NIOSH 1990a,b]. These analogs occur in a different mineral “habit” 

and are often referred to as cleavage fragments. PCM, the analytical method routinely used 

for characterizing airborne exposures, is incapable of differentiating these nonasbestiform 

analogs from asbestos fibers on the basis of physical appearance. To address these concerns 

and ensure that employees are protected, NIOSH defined “airborne asbestos fibers” to 

encompass not only fibers from the six asbestos minerals (chrysotile, crocidolite, amosite, 

anthophyllite asbestos, tremolite asbestos and actinolite asbestos) but also elongate mineral 

particles from their nonasbestiform analogs as a precautionary measure. NIOSH retained the 

use of PCM for measuring airborne fiber concentrations and counting those elongate mineral 

particles having an aspect ratio of 3:1 or greater and a length greater than 5 μm. The REL 

(0.1 f/cc) was set at the limit of quantification for the PCM analytical method for a 400-liter 

sample, but risk estimates indicated that exposure at 0.1 f/cc throughout a working lifetime 

would be associated with a residual risk for lung cancer. No risk-free level of exposure to 

airborne asbestos fibers has been established [NIOSH 1976, 1984, 2011]. More information 

on asbestos from NIOSH can be found at http://www.cdc.gov/niosh/docs/2011-159/.

Libby amphibole is a complex mixture of amphibole fibers found in the rocks and ore of 

Zonolite Mountain, 6 miles northeast of Libby, Montana (Figure 1). The mixture primarily 

includes tremolite, winchite, and richterite fibers with trace amounts of other minerals. 

These fibers exhibit a complete range of morphologies from prismatic crystals to asbestiform 

fibers [Meeker et al. 2003]. Zonolite Mountain contains a large vermiculite deposit that has 

been mined since the early 1920s for various commercial uses. Vermiculite miners, mill 

employees, and those working in the processing plants were exposed to these amphibole 

fibers, which remain within vermiculite ore and product. As amphibole asbestos is present 

in the geological deposit from which the vermiculite ore was being mined, employees were 

exposed to asbestos fibers during various activities such as extracting ore from the 
Health Hazard Evaluation Report 2012-0077-3223 Page 29

mine, transporting ore and waste rock, milling operations and shipping the final product 

[Meeker et al. 2003]. 

Inhalation exposure to asbestos can result in a scarring disease of the lung known as 

asbestosis, inflammation of the chest cavity (pleuritis) with or without fluid build-up, lung 

cancer, and another type of cancer known as malignant mesothelioma. The risk of these 

diseases, which can be disabling or fatal, generally increases with intensity and duration of 

exposure. The risk of lung cancer from inhaling asbestos fibers is also increased in smokers. 

Most people who get asbestos-related diseases have been exposed to high levels of asbestos 

for a long time. Most asbestos-related diseases rarely occur until at least 15 years after 

first exposure to asbestos. All forms of asbestos are hazardous, and all can cause cancer, 

but amphibole forms of asbestos are considered to be somewhat more hazardous to health 

than chrysotile [ATSDR 2001]. Asbestos fibers have no detectable odor or taste and fibers 

associated with these health risks are too small to be seen with the naked eye. A summary of 

asbestos-related diseases are listed below:

● Asbestosis – a serious, progressive, long-term disease of the lungs. It is caused by 

inhaling asbestos fibers that irritate lung tissues and cause the tissues to scar. The 

scarring makes it hard for oxygen to get into the blood. 

● Lung cancer – people who mine, mill or manufacture asbestos, and those who use 

asbestos, and products containing asbestos, are more likely than the general population 

to develop lung cancer, as well as other cancers of the respiratory tract, including 

tracheal, laryngeal and bronchial cancers. 

● Mesothelioma – a rare form of cancer that is found in the thin membrane lining (pleura) 

of the lung, chest, abdomen, and heart. The vast majority of cases are linked to asbestos 

exposure. 

Exposure may also occur through ingesting (swallowing) asbestos, especially where airborne 

asbestos may deposit in the nose and mouth. Although some gastrointestinal cancers have 

been reported in asbestos-exposed employees, the evidence is considered suggestive, but not 

sufficient, to link asbestos exposure to those cancers [IOM 2006]. 

Exposure to Libby amphibole results in the same types of adverse health effects as are seen 

with exposure to other asbestos fibers. Mortality and morbidity studies on the mine and 

mill workers from Libby have reported adverse health effects in these employees including 

lung cancer, mesothelioma, nonmalignant respiratory disease, asbestosis, pleural anomalies, 

interstitial fibrosis, and altered lung function epidemiologic studies of workers exposed to 

Libby amphibole asbestos fibers indicate increased lung cancer and mesothelioma, as well 

as asbestosis and other nonmalignant respiratory diseases [Amandus and Wheeler 1987; 

Amandus et al. 1987; Peipins et al. 2003; Sullivan 2007; Larson et al. 2010]. 
Page 30 Health Hazard Evaluation Report 2012-0077-3223

Asbestos minerals are widespread in the environment. They may occur in large natural 

deposits, or as contaminants in other minerals. Low levels of asbestos can be detected 

in almost any air sample. The results of numerous measurements indicate that average 

concentrations of asbestos in ambient outdoor air are within the range of 10−8 to 10−4 PCM 

f/cc; levels in urban areas may be an order of magnitude higher than those in rural areas 

[ATSDR 2001]. In indoor air, the concentration of asbestos depends on whether asbestos 

was used for insulation, ceiling or floor tiles, or for other purposes, and whether these 

asbestos-containing materials are in good condition or are deteriorated and easily crumbled. 

Concentrations measured in homes, schools and other buildings that contain asbestos 

range from about 0.00003–0.006 f/cc. Indoor air concentrations of asbestos ranged from 

approximately 10−5 to 10−4 f/cc in a study of air concentrations measured in 315 U.S. public 

and commercial facilities [ATSDR 2001].
Health Hazard Evaluation Report 2012-0077-3223 Page 31

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Page 34 Health Hazard Evaluation Report 2012-0077-3223

Keywords: North American Industry Classification System 115310 (Support Activities for 

Forestry), Montana, Libby Amphibole, asbestos, forest
Health Hazard Evaluation Report 2012-0077-3223 Page 35

The Health Hazard Evaluation Program investigates possible health hazards in the workplace 

under the authority of the Occupational Safety and Health Act of 1970 (29 U.S.C. § 669(a)

(6)). The Health Hazard Evaluation Program also provides, upon request, technical assistance 

to federal, state, and local agencies to investigate occupational health hazards and to prevent 

occupational disease or injury. Regulations guiding the Program can be found in Title 42, Code 

of Federal Regulations, Part 85; Requests for Health Hazard Evaluations (42 CFR Part 85).

Disclaimer

The recommendations in this report are made on the basis of the findings at the workplace 

evaluated and may not be applicable to other workplaces.

Mention of any company or product in this report does not constitute endorsement by NIOSH.

Citations to Web sites external to NIOSH do not constitute NIOSH endorsement of the 

sponsoring organizations or their programs or products. NIOSH is not responsible for the 

content of these Web sites. All Web addresses referenced in this document were accessible as of 

the publication date.

Acknowledgments

Analytical Support: Bureau Veritas North America

Desktop Publisher: Shawna Watts

Editor: Ellen Galloway 

Logistics: Donnie Booher, Karl Feldmann

Availability of Report

Copies of this report have been sent to the employer, employees, and union at the facility. 

The state and local health department and the Occupational Safety and Health Administration 

Regional Office have also received a copy. This report is not copyrighted and may be freely 

reproduced. 

This report is available at http://www.cdc.gov/niosh/hhe/reports/pdfs/2012-0077-3223.pdf.

Recommended citation for this report:

NIOSH [2014]. Health hazard evaluation report: evaluation of employee exposures 

to Libby amphibole asbestos during forest management activities in the Kootenai 

National Forest. By Butler C, McCleery R, Kiefer M, Harper M, Lee E, Wallingford K. 

Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease 

Control and Prevention, National Institute for Occupational Safety and Health, NIOSH 

HHE Report No. 2012-0077-3223.
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