Evaluation of Wildland Fire 

Fighters' Exposures to Asbestos 

During a Prescribed Burn

HHE Report No. 2017-0076-3352

June 2019
Authors: Michael P. Grant, ScD

Analytical Support: Maxxam Analytics

Desktop Publisher: Jennifer Tyrawski

Editor: Cheryl Hamilton

Industrial Hygiene Field Assistance: Catherine Beaucham, Donald Booher, Guadalupe Gomez

Logistics: Donald Booher, Kevin Moore

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

Forestry), Montana, Wildland, Firefighting, Prescribed Burn, Asbestos, Libby Amphibole, Mine 

Disclaimer

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 USC 669a(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]. 

Availability of Report

Copies of this report have been sent to the employer, employees, and union at the federal forest

management agency. The state and local health departments and the Occupational Safety and

Health Administration Regional Office have also received a copy. This report is not copyrighted and

may be freely reproduced.

Recommended Citation

NIOSH [2019]. Evaluation of wildland fire fighters’ exposures to asbestos during a prescribed burn.

By Grant, MP. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for

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

Hazard Evaluation Report 2017-0076-3352, https://www.cdc.gov/niosh/hhe/reports/pdfs/2017-

0076-3352.pdf. 
Table of Contents

Main Report

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

Our Approach ................................................................................................................................................... 1

Our Key Findings.............................................................................................................................................. 1

Our Recommendations.................................................................................................................................... 2

Supporting Technical Information 

Section A: Workplace Information............................................................................................................ A-1

Workplace.................................................................................................................................................. A-1

Employee Information ............................................................................................................................ A-1

Process Description ................................................................................................................................. A-1

Section B: Methods, Results, and Discussion .......................................................................................... B-1

Methods: Observations of Work Processes and Practices................................................................. B-1

Results: Observations of Work Processes and Practices.................................................................... B-1

Methods: Exposure Assessment ............................................................................................................ B-3

Results: Exposure Assessment ............................................................................................................... B-3

Discussion ................................................................................................................................................. B-4

Limitations................................................................................................................................................. B-5

Conclusions............................................................................................................................................... B-5

Section C: Tables.......................................................................................................................................... C-1

Section D: Occupational Exposure Limits............................................................................................... D-1

Asbestos.................................................................................................................................................... D-2

Health Effects.......................................................................................................................................... D-3

Section E: References.................................................................................................................................. E-1
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1

Introduction

Request

Management at a federal forest management agency was concerned about wildland fire fighters’ 

exposures to asbestos during prescribed burns near a former vermiculite mine.

Workplace

This federal forest management agency is responsible for approximately 28,000 acres of Kootenai 

National Forest. Within this zone, approximately 10,000 acres of land are centered on a former 

vermiculite mine. The geological deposit where the vermiculite was mined contains amphibole asbestos. 

The prescribed burn in this evaluation was just outside of this area.

To learn more about the workplace, go to Section A in the Supporting Technical Information

Our Approach

During our two visits to the worksite, we completed the following activities:

• Reviewed the respiratory protection program.

• Observed work processes and practices.

• Collected air samples for asbestos and total fibers.

To learn more about our methods, go to Section B in the Supporting Technical Information

Our Key Findings

Exposures to total fibers in air were less than the lowest occupational exposure limit 

• We saw the highest concentrations during tasks with greater plant and soil disturbance and 

where water was not used (e.g., fire line construction and dry mop-up). 

• We detected small numbers of asbestos fibers in the air samples we collected. The tasks 

associated with the most asbestos fibers were fire line construction and dry mop-up.

Decontamination line procedures could be improved

• Some confusion and inconsistencies existed around the decontamination line procedures 

because this was one of the first times these procedures were used during a live event. Some 

decontamination steps did not focus on particulate or fiber decontamination, and not all 

employees went through the same level of decontamination as others did.
2

• Some employees were not aware of the overall purpose and intended effectiveness of the 

decontamination process.

The respiratory protection program could be strengthened 

• We observed that the fit testing equipment used was not calibrated according to the 

manufacturer’s specifications.

• We saw fire fighters with facial hair. This would affect the ability of the respirator to get a good 

seal against an employee’s face.

To learn more about our results, go to Section B in the Supporting Technical Information

Our Recommendations

The Occupational Safety and Health Act requires employers to provide a safe workplace.

Benefits of Improving Workplace Health and Safety:

 Improved worker health and well-being  Enhanced image and reputation 

 Better workplace morale  Superior products, processes, and services

 Easier employee recruiting and retention  May increase overall cost savings

The recommendations below are based on the findings of our evaluation. For each recommendation, 

we list a series of actions you can take to address the issue at your workplace. The actions at the 

beginning of each list are preferable to the ones listed later. The list order is based on a well-accepted 

approach called the “hierarchy of controls.” The hierarchy of controls 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 practical, administrative 

measures and personal protective equipment might be needed. Read more about the hierarchy of 

controls at https://www.cdc.gov/niosh/topics/hierarchy/. 

We encourage the company to use a health and safety committee to discuss our 

recommendations and develop an action plan. Both employee representatives and 

management representatives should be included on the committee. Helpful guidance can be 

found in “Recommended Practices for Safety and Health Programs” at

https://www.osha.gov/shpguidelines/index.html. 
3

Recommendation 1: Use wet mop-up methods whenever possible

Why? Wet methods are better for preventing exposures to hazardous dusts, particles, or fibers. Water 

helps keep the dust, particles, or fibers from getting into the air. Water can also suppress dust, 

particles, and fibers that have already become airborne and can minimize the distance that they travel. 

We saw that dry mop-up produced more visual dust than wet mop-up. Most of the asbestos fibers we 

measured occurred during dry mop-up tasks. Wherever possible, wet methods should be used.

How? At your workplace, we recommend these specific actions:

Use wet mop-up methods instead of dry mop-up methods.

• Using wet methods or a combination of wet and dry methods will further reduce the 

amount of dust and potential asbestos exposures.

Recommendation 2: Review the decontamination line setup

Why? Decontamination lines protect employees from exposures to hazardous substances that may 

have contaminated the personal protective equipment, tools, and vehicles used in the burn. A wellconstructed decontamination line protects employees by minimizing or eliminating the migration of 

hazardous substances from dirty areas into clean areas 

(https://www.osha.gov/SLTC/hazardouswaste/training/decon.html).

We observed some confusion, inconsistencies, and deviation from written protocol around the 

decontamination line procedures. The decontamination line could be improved with better 

communication and training.

How? At your workplace, we recommend these specific actions:

Talk with employees about the effectiveness of decontamination.

• Explain to employees that the decontamination process is designed to remove 

contaminant from the gear before leaving the fire zone. So fire packs that have been 

decontaminated thoroughly with high efficiency particulate air-filtered vacuums and/or 

water are clean and present minimal risk of exposure once dry.

The decontamination line should be open and ready to receive fire fighters 

before they enter the fire zone.

• Be prepared to decontaminate and remove fire fighters from the fire zone immediately 

if an emergency arises. Do not allow fire fighters to enter the fire zone without the 

decontamination line being set up first. 
4

Follow a decontamination plan focused on particulate or 

fiber contamination.

• Do not include a chlorine bath step if asbestos is the only contaminant of concern—

chemical rinses do not eliminate asbestos.

• Do not use biohazard bags unless disposing of a biological hazard. Use asbestos 

disposal bags instead.

• Consider adding a high efficiency particulate air vacuum to the gross decontamination 

step. It is an effective method to remove dust and particulates from fabric and other 

surfaces, such as radios or other equipment that should not get wet during 

decontamination. If you decide to use these vacuums, establish appropriate protocols 

for emptying the vacuum and cleaning the filters.

Avoid deviating from decontamination line standard operating procedures.

• Fire zone employees should go through the decontamination line first. The 

decontamination line employees should go through the line once all fire zone employees 

have been decontaminated.

• Employees furthest away from the clean side should start going through the 

decontamination line first.

Provide training on decontamination line setup, use, and breakdown.

• Practice dry runs of setting up and breaking down the decontamination line to improve 

efficiency during live events. This training should focus on the following:

o Never backtrack while in the decontamination line. Individuals moving through 

the line should always be moving from the dirty side to the clean side. If current 

practices involve moving people from the clean side to the dirty side, adjust 

those practices.

o Do not allow employees to skip parts of the decontamination line. Every 

employee should go through the decontamination process as it is written in your 

standard operating procedures.

o Develop a standard operating procedure to keep pools that catch contaminated 

water clean. We observed buildup of debris in the boot wash station. Empty the 

pools more frequently to prevent excessive buildup. 

o Do not allow employees working on the decontamination line to break down 

equipment like a chainsaw. Instead, instruct the individual going through the 

decontamination line to break down the tool. The decontamination line employee 

can then clean the parts of the tool.

• Avoid dry sweeping, and incorporate high efficiency particulate air vacuums if feasible.
5

Clean all equipment after each fire event.

• There were totes were left over from previous fire events. Handling the gear left inside 

could cause a resuspension of dust. Cleaning all gear after each event will eliminate the 

risk of resuspension when handling the gear in the future.

Recommendation 3: Strengthen your respiratory protection program

Why? Because respiratory protection is required for certain tasks, a respiratory protection program is 

also required. Mandatory respiratory protection programs must be in compliance with the 

Occupational Safety and Health Administration (OSHA) respiratory protection standard, 29 CFR 

1910.134. This program must be a written program that documents worksite-specific procedures 

requiring respirator use as well as identifying a competent program administrator. Requirements 

include annual fit testing, documented training, and medical clearance, among other things.

We identified some technical issues that affected the validity of fit testing results during one of our 

visits. We also saw employees with facial hair and noted that your fit testing equipment calibration 

was not up to date according to manufacturer’s recommendations.

How? At your workplace, we recommend these specific actions:

Perform fit tests and calibrate fit testing equipment annually.

• Make sure all employees required to wear a respirator are fit tested prior to the start of 

each fire season.

• Follow the manufacturer’s recommendations related to calibration and maintenance of 

the fit testing equipment. This will ensure that equipment is operating as intended.

Inspect your equipment thoroughly before each use.

Provide annual respiratory protection training.

• Provide more frequent training to employees on the appropriate donning and doffing 

procedures. Some employees had difficulty donning and doffing their respiratory 

protection. Employees were observed helping each other navigate this process.
6

Develop a plan for addressing employees who arrive to a burn with 

facial hair.

• Provide training to increase awareness around the importance of having a tight seal.

• Offer a mechanism for employees to correct the issue (e.g., keep disposable razors on 

site in case they are needed).
Supporting Technical Information

Evaluation of Wildland Fire Fighters’ Exposures to 

Asbestos During a Prescribed Burn

HHE Report No. 2017-0076-3352

June 2019
A-1

Section A: Workplace Information

Workplace

Various forest management activities, including fire response and prescribed burns, are performed 

within an area of national forest (approximately 28,000 acres) overseen by a federal forest management

agency. Within the forest management area is a zone known as Operable Unit 3 (OU3) by the United 

States Environmental Protection Agency (EPA). OU3 surrounds a former vermiculite mine and areas 

impacted by the releases from the mine. OU3 is approximately 10,000 acres centered on the mine and is 

an EPA National Priorities List Superfund site. The National Priorities List contains sites with known 

releases of hazardous substances throughout the United States. The boundary of OU3 changes from 

year to year. The prescribed burn in this evaluation was just outside of OU3. 

Employee Information

• Among 19 employees, 6 worked on the decontamination line, and 13 worked in various 

capacities as fire fighters.

• All employees worked a single shift lasting approximately 12 hours on the day of a 

prescribed burn.

• Most employees belonged to a union.

Process Description

The prescribed burn day had five parts: briefing and preparation, fire line construction, burn, mop-up, 

and decontamination.

Briefing and Preparation

On the morning of the prescribed burn, employees gathered at the ranger station to prepare for the day. 

The agency follows Incident Command Structure (ICS), so the entire group reviewed the Incident 

Action Plan. The plan lays out all pertinent information for the prescribed burn including safety, 

communications, logistics, and weather. After the briefing, employees prepared their fire packs, dressed 

in their wildland fire gear, and ensured that their powered air purifying respirators (PAPRs) were 

working. Employees then put their packs onto various vehicles and departed for the site of the burn. 

Different types of vehicles were used including fire trucks, a decontamination equipment truck, utility 

task vehicles (UTVs), and personal vehicles.

Fire Line Construction

Fire fighters put on their PAPRs prior to leaving the cold zone (the “clean” side of the decontamination 

line) and entering the fire zone (the “dirty” side of the decontamination line). The fire trucks departed 

for the burn site, and UTVs shuttled fire fighters into the site. Fire fighters worked to construct a fire 

line around the perimeter of the proposed burn site (Figure 1). They were able to utilize existing forest 

roads along two sides of the burn site, reducing the amount of fire line construction necessary 
A-2

(Figure 2). Fire hose was laid along those lines to ensure access to water across the burn area. One fire 

fighter used a leaf blower to clear debris from the fire line. Another fire fighter used a chainsaw to 

manage the fuel (e.g., grass, brush, or timber) within the burn zone, preparing it for the burn.

Figure 1. Fire fighters using tools to construct a fire line by digging into the forest floor to create a 

break in the fuel. Photo provided by employer.

Figure 2. Diagram of the burn site showing fire lines and forest road boundaries. A fire line cuts 

through the middle of the burn area in order to make it easier to move from one side to the other. The 

division of wet and dry mop-up is also indicated. Figure by NIOSH.
A-3

Prescribed Burn

Two fire fighters were tasked with ignition duties once the fire line was constructed. They walked the 

perimeter of the burn lighting the fire with drip torches (Figure 3). Fire fighters spread out across the 

perimeter of the fire once it was lit and let it burn for approximately 100 minutes. During this time, fire 

fighters worked to keep the fire from crossing the fire line and, where appropriate, from climbing too 

high up tree trunks (Figure 4).

Figure 3. Fire fighter using a drip torch to start the burn. Photo provided by employer.

Figure 4. Fire moving along the planned burn area along the fire line. Photo provided by employer.
A-4

Mop Up 

Fire fighters were assigned to either wet or dry mop-up duties to put out the fire completely (Figure 5). 

Wet mop-up methods were used on the east side of the burn and dry mop-up methods were used on 

the west side (Figure 2). Wet mop-up uses water to put out the fire. Dry mop-up uses physical 

disruption of the soil and roots to put out the fire. Three fire fighters were assigned to wet mop-up, and 

seven were assigned to dry mop-up. The remaining three fire fighters served in supervisory roles and 

helped with mop up as necessary.

Figure 5. Fire fighters performing wet and dry mop-up activities. The fire fighter on the wet mop-up

side of the line is using the hose to apply water. The dry mop-up side of the line is using the hand tool 

to dig and turn soil to extinguish the fire. Photo provided by employer.

Decontamination

Fire fighters were sent through the decontamination line at staggered times once the fire was under 

control. Employees working on the decontamination line were responsible for breaking down and 

cleaning the equipment and tools at each step. First, UTVs dropped the fire fighters at the beginning of 

the decontamination line where they left any tools (e.g., chainsaw) that they had used. We then observed 

the fire fighters go through these steps:

1. Remove fire pack, detach PAPR from fire pack, and keep PAPR and facemask on.

2. Place radio and helmet on table.

3. Proceed to gross decontamination of boots. Wet down boots, remove boots, and discard laces.

4. Perform gross decontamination rinse with clothing and PAPR on.

5. Move to decontamination trailer.

6. Remove wildland fire clothing, and keep PAPR on.

7. Enter “dirty” side of the trailer. Keep PAPR on. Cut or remove undershirt and undress.
A-5

8. Move into shower stalls and rinse head to toe in shower with PAPR on.

9. Remove PAPR. Move backward in decontamination line (“upstream”) to hang PAPR on hook.

10. Move into shower stalls and shower with soap and shampoo.

11. Proceed to clean side of trailer, put on personal clothing, and exit trailer.

Fire fighters gathered at a resting area after decontamination was complete to wait for the remainder of 

the fire fighters to complete decontamination. UTVs were decontaminated at the station where tools 

were dropped before being driven out of the fire zone.
B-1

Section B: Methods, Results, and Discussion

Methods: Observations of Work Processes and Practices 

On one visit, we observed the fit testing procedures and storage areas for equipment. On a second visit, 

we evaluated the use of personal protective equipment (PPE) and the decontamination line during a 

prescribed burn.

Results: Observations of Work Processes and Practices

Fit Testing

• We observed fit testing procedures as part of this evaluation. Fire fighters are required to be fit 

tested annually. Many of the employees who respond in or around OU3 are stationed in other 

parts of the forest full time or are seasonal fire fighters. 

• This agency used quantitative fit testing methods (PortaCount, TSI Inc.). The PortaCount used 

had not been calibrated according to the manufacturer’s recommendations. The manufacturer 

recommends that the instrument be calibrated annually.

• We observed that the tube connecting the PortaCount to the PAPR mask through the air hose 

was twisted and pinched just enough to allow some air through but not enough to register an 

error on the machine. The pinched tube was causing automatic passes for all fit tests.

• We advised the agency to adjust their practices to avoid getting the PortaCount tube twisted up 

in the hose of the PAPR. We also advised them to re-test any employees who had been fit tested 

recently. After identifying these issues, the worksite made efforts to re-fit test employees prior to 

the prescribed burn and fire season. All employees participating in the prescribed burn were refit tested before the burn. 

• Some employees had facial hair, which can affect the ability to get a good seal of the respirator 

to the face.

Storage

All fire fighters had their own tote where they stored their equipment. The agency used different 

colored tops for the totes to indicate whether the equipment inside was clean (black) or dirty (red). If an 

event were to last multiple days, the fire fighters might not clean certain items and simply store them in 

the red topped tote. Fire fighters discarded or cleaned all gear and washed out the totes at the end of an 

event. At the time of our first visit, we recommended that they store their black and red totes in 

separate areas to minimize the chances of someone mistaking the dirty totes for clean ones. When we 

arrived for our second visit, the totes were stored in separate areas.

Prescribed Burn

• Fire fighters were required to wear a wildland fire shirt and pants, tall leather boots, a fire pack 

with a fire shelter, a full-face elastomeric PAPR, leather gloves, and a fire helmet. 
B-2

• Employees working on the decontamination line were required to wear a Tyvek® suit with hood, 

shoe covers, half-face elastomeric air purifying respirator with P100 cartridges, nitrile gloves, 

safety glasses, and a fire helmet.

• Fire fighters removed their PAPRs and fire packs for the drive over to the burn site after the 

morning briefing and equipment preparation.

• Fire fighters drove two fire trucks, two UTVs, and the decontamination equipment truck to the 

burn site. A water truck and the decontamination trailer were already on site.

• Fire fighters were sent into the fire zone to begin fire line construction before the 

decontamination line was operational.

• Many fire fighters had drinking tubes in their respirator masks.

• We observed employees dry sweeping to clean out the bottom of the decontamination 

equipment truck after the event. The employees cleaning the truck were not wearing 

respiratory protection.

Decontamination

• The decontamination line was not set up prior to the fire fighters entering the fire zone to 

begin working. 

• One of the steps in the decontamination process was to clean PAPR hoses in a chlorine bath.

• Pools used to catch water from boot rinsing were not changed between each person. These 

pools filled with contaminated water quickly.

• Biohazard (red) bags were used to collect discarded items.

• Two high efficiency particle air (HEPA) filter vacuums were available, but they were not used 

during the decontamination process.

• We were told that decontamination employees cleaned out some totes during the burn that 

contained contaminated gear from a previous event. We did not directly observe this process.

• Decontamination employees were helping, rather than instructing, fire fighters during some of 

the steps in the process. 

• Steps for entering the decontamination trailer “dirty” side and removing the PAPR involved 

moving upstream (backward) through the decontamination line.

• Some employees voiced concerns that dried fire packs that had gone through the 

decontamination line could expose or harm them. 

• Fire fighters gathered at a resting area after decontamination was complete to wait for the 

remainder of the fire fighters to complete decontamination. A table and some chairs were set up, 

but some fire fighters chose to sit on the ground.
B-3

• Employees working on the decontamination line broke down the line and then went through a 

shorter, dry decontamination procedure after all fire fighters passed through the 

decontamination line. These employees removed their protective Tyvek suits and shoe covers, 

wiped their faces and exposed skin, removed their respirators, and wiped their faces again. These 

employees then moved directly into the cold zone without passing through the trailer or using 

the gross wet decontamination methods used for the fire fighters.

Methods: Exposure Assessment 

• We collected a series of task-based personal air samples that covered the entire shift for 

19 employees. 

• We analyzed each sample for total fibers using the National Institute for Occupational Safety 

and Health (NIOSH) Method 7400. This method uses Phase Contrast Microscopy (PCM).

• We analyzed a subset of samples for asbestos fibers using NIOSH Method 7402. This method 

uses Transmission Electron Microscopy (TEM). For samples that became overloaded, we first 

used International Organization for Standardization (ISO) Method 13794 via indirect 

preparation, and then we analyzed them using NIOSH Method 7402.

• We changed the sampling media between every step in the burn process (e.g., between fire line 

construction and the burn) as well as when we suspected that samples were in danger of 

being overloaded. 

• We visually inspected the filters as often as possible to determine when to change them. If we 

saw any sign of color on the filter, we changed it, because no conventional method existed in 

this setting to determine when a sample became overloaded.

Results: Exposure Assessment

Fibers by Phase Contrast Microscopy

Although we tried to minimize the possibility, some samples taken on fire fighters during the prescribed 

burn were overloaded with debris. None of the samples collected on the decontamination employees 

were overloaded. The overloaded samples could not be analyzed for total fiber counts, and we could 

not calculate a time-weighted average (TWA) that could be compared directly to an occupational 

exposure limit (OEL). However, we were able to analyze the overloaded samples for the presence of 

asbestos fibers. 

• For the 55 task samples that were not overloaded, all exposures to fibers in air were below the 

lowest OEL. For asbestos, the OSHA permissible exposure limit (PEL), the NIOSH 

recommended exposure limit (REL), and the American Conference of Governmental Industrial 

Hygienists® (ACGIH) threshold limit value® (TLV) are 0.1 fibers per cubic centimeter of air 

(f/cc).

• For samples that were not overloaded with debris, task-based fiber concentrations ranged from 

0.0013 through 0.13 f/cc for fire fighters (Table C1). The highest concentrations came during 

mop-up (average = 0.065 f/cc) and fire line construction (average = 0.031 f/cc) activities. The 
B-4

lowest concentrations were found in the samples taken while traveling to the burn site (average 

= 0.0061 f/cc) and after going through the decontamination line (average = 0.018 f/cc). All 

samples collected during the burn and many of the samples collected during the mop-up 

were overloaded. 

• For employees on the decontamination line, full-shift TWA fiber concentrations ranged from 

0.0016 through 0.050 f/cc (average = 0.013 f/cc) (Table C2).

Asbestos Fibers by Transmission Electron Microscopy

We detected 13 asbestos fibers (12 Tremolite and 1 Richterite) in the samples that were analyzed using 

TEM (Table C3). The greatest number of asbestos fibers were detected during the mop-up (six fibers) 

and fire line construction (four fibers) tasks. Five of the six fire fighters who had asbestos fibers 

detected during mop-up activities were assigned to the dry mop-up task. The sixth fire fighter’s time 

was split between wet and dry mop-up. There was one fiber detected on a sample taken during the 

burn, one fiber detected on a sample taken after decontamination (these samples covered the time 

period between when an employee finished going through the decontamination line through leaving the 

burn site), and one fiber detected on a sample taken on a decontamination employee during the burn.

Discussion 

We found low concentrations of total fibers in the air during prescribed burn activities. The highest 

concentrations were detected during tasks with greater plant and soil disturbance (e.g., fire line 

construction and mop-up). Most exposures to total fibers in air were below all applicable OELs, 

although, one fire fighter had a task concentration of 0.13 f/cc during dry mop-up. Because this sample 

was approximately one hour long, the employee was not overexposed. However, if this employee was to 

perform mop-up activities for the entire day, the OSHA PEL of 0.1 f/cc may be exceeded. 

We were not able to determine fiber concentrations in air during the burn work tasks due to 

overloading of the filters. It is likely that the filters were overloaded due to an excess of organic material 

resulting from the burning vegetation. It is also very likely that the greatest potential for exposure to 

asbestos fibers would be during the fire line construction and mop-up tasks, as these activities have the 

greatest direct disruption of soil. This latter assumption is supported by our TEM analyses, which found 

that tasks associated with detection of the most asbestos fibers were the fire line construction and mopup tasks.

We detected multiple asbestos fibers on a subset of the air samples. The tasks associated with the most 

asbestos fibers were fire line construction and dry mop-up. This is likely due to the amount of soil and 

plant disturbance and the lack of water used in these tasks. Water is an excellent method for controlling 

dust exposures in many occupational settings, so wet mop-up methods should be used when possible. 

We are unsure about the origin of the one asbestos fiber found after the decontamination process was 

finished. The concentration of total fibers for the sample was 0.032 f/cc, which was below the OEL for 

total fibers of 0.1 f/cc (Table C1). The concentration was also the highest concentration detected 

among fire fighters during that task (range: not detected–0.032 f/cc). The exposure occurred while an 

employee was sitting on the ground after going through the decontamination line. A lot of debris was 

not disturbed, however, asbestos is endemic to the region, especially near the mine. 
B-5

It is also unclear where the asbestos fiber found on the decontamination employee’s sample may have 

come from. The sample that this fiber was found on was collected during the burn and 

decontamination process. It had the second highest concentration of fibers (0.009 f/cc) out of the 

employees working on the decontamination line (average = 0.013 f/cc). This exposure may have come 

from working closely with contaminated fire fighters and gear that moved through the decontamination 

line or from cleaning out totes with contaminated gear during the burn. These totes were left over from 

previous fire events, and there could have been a re-suspension of dust during the handling of this gear. 

During our visit was one of the first times that this decontamination process was implemented in a live 

situation. Some confusion and inconsistencies around the decontamination line procedures occurred, 

for example, the line was not fully set up before the fire fighters entered the fire zone; decontamination 

line employees did not undergo the same decontamination procedures as fire fighters (a deviation from 

the written protocol); and some steps did not apply to particulate or fiber decontamination (i.e., an 

unnecessary chlorine bath step for PAPR hoses). Additionally, decontamination line employees gave 

help instead of just instruction to fire fighters, thereby, increasing line employees’ risk of contamination. 

We also learned that some employees were concerned that they could be exposed to asbestos when 

handling fire packs that had been through the decontamination line and had dried. Fire packs that have 

been decontaminated thoroughly with HEPA vacuums and/or water are clean and present minimal risk 

of exposure when they dry. The decontamination process is designed to remove contaminant from the 

gear before leaving the fire zone.

Some areas of the respiratory protection program could be improved. This includes providing annual fit 

testing for all employees required to wear respirators and calibrating the fit testing equipment according 

to the manufacturer’s recommendations. Another area for improvement would be confirming that 

employees shave before wearing respirators to ensure a tight seal between the face and the respirator.

Limitations 

This evaluation is subject to several limitations. First industrial hygiene sampling can only document 

exposures on the days of sampling in the locations sampled. These results may not be representative of 

conditions during other days. Although steps were taken to select the samples with the greatest 

likelihood for having asbestos fibers, there could have been additional asbestos fibers on the samples 

that were not analyzed by TEM. In addition, the small size and homogenous nature of the population 

sampled limit the generalizability of our evaluation results.

Conclusions

All exposures to total fibers in air were below the lowest OEL—these concentrations were able to be 

determined for samples that were not overloaded with debris. Fibers, including asbestos fibers, were 

detected during multiple tasks performed throughout the prescribed burn. The majority of fibers were 

found during dry activities and during tasks associated with greater plant and soil disturbance, such as 

fire line construction and dry mop-up. Using wet mop-up procedures whenever possible could decrease 

fiber exposures. Reworking decontamination line procedures and setup and improving the respiratory 

protection program will further protect employees from fiber exposures. 
C-1

Section C: Tables

Table C1. Personal breathing zone samples for fibers analyzed by phase contrast microscopy for fire fighters during a prescribed burn

Task: Travel to burn site Fire line construction Burn Mop-up After decontamination

Fire fighter # Time 

(min)

Concentration 

(f/cc)*†

Time 

(min)

Concentration 

(f/cc)*†

Time 

(min)

Concentration 

(f/cc)*†

Time 

(min)

Concentration 

(f/cc)*†

Time 

(min)

Concentration 

(f/cc)*†

1 283 0.0096 104 0.012 88 Overloaded 93 0.043 100 Not detected

2 324 Not detected 46 0.018 98 Overloaded 73 0.026 116 Not detected

3 300 0.0059 76 0.029 103 Overloaded 152 Overloaded 41 0.022

4 80 0.0036 12 0.018 155 Overloaded 41 Overloaded 83 0.023

5 310 0.0085 48 Overloaded 100 Overloaded 142 Overloaded 70 0.0013

6 285 Not detected 96 Not detected 81 Overloaded 118 0.061 80 Not detected

7 312 0.0051 50 0.052 108 Overloaded 148 Overloaded 21 Not detected

8 278 0.0040 93 0.022 80 Overloaded 127 Overloaded 82 Not detected

9 315 0.0035 50 0.027 97 Overloaded 118 Overloaded 86 0.011

10 294 0.011 86 0.032 81 Overloaded 146 Overloaded 68 0.022

11 283 0.0045 88 0.049 93 Overloaded 140 Overloaded 56 0.032

12 326 0.0064 50 0.039 106 Overloaded 62 0.13 110 0.016

13 279 0.0046 95 0.046 75 Overloaded 148 Not detected 60 Not detected

*The minimum detectable concentrations ranged 0.002–0.03 f/cc.

†OSHA, NIOSH, and ACGIH have OELs of 0.1 f/cc for asbestos. OSHA has a short-term excursion limit of 1 f/cc.
C-2

Table C2. Personal breathing zone samples for fibers analyzed by phase contrast microscopy for 

decontamination employees during a prescribed burn

Employee Travel to burn site* Prescribed burn† Time-weighted 

average (f/cc)‡ 

 Time (min) Concentration (f/cc) Time (min) Concentration (f/cc) 

1 295 Not detected§ 414 0.0079 0.0016

2 339 0.010 373 0.086 0.050

3 341 0.0027 374 0.0090 0.0060

4 332 0.0034 365 0.0079 0.0058

5 339 0.0071 379 0.0065 0.0068

6 338 0.0050 374 0.0064 0.0057

*These samples included prepping gear, safety briefing, gathering gear, loading trucks, driving to the site, 

further briefing, and then lunch. 

†These samples spanned the entire prescribed burn, including fire line construction, burn, and mop-up 

activities.

‡OSHA, NIOSH, and ACGIH have occupational exposure limits of 0.1 f/cc for asbestos. OSHA has a shortterm excursion limit of 1 f/cc. 

§The minimum detectable concentration was 0.002 f/cc.
C-3

Table C3. Personal breathing zone samples for asbestos 

analyzed by transmission electron microscopy (TEM) for 

fire fighters and decontamination employees during a 

prescribed burn

Employee Task Number and 

type of fiber 

detected by TEM

Fire fighter #1 Burn 0 

 Mop-up (dry) 0 

Fire fighter #2 Burn 0 

 Mop-up (dry) 0 

Fire fighter #3 Fire line construction 0 

 Burn 0 

 Mop-up (wet/dry) 0 

 After decontamination 0 

Fire fighter #4 Burn 0 

 Mop-up (wet/dry) 1 (Richterite)

 After decontamination 0 

Fire fighter #5 Fire line construction 0 

 Burn 1 (Tremolite)

 Mop-up (dry) 1 (Tremolite)

Fire fighter #6 Burn 0 

 Mop-up (dry) 4 (Tremolite)

Fire fighter #7 Fire line construction 2 (Tremolite)

 Burn 0 

 Mop-up (dry) 0 
C-4

Table C3 (continued). Personal breathing zone samples for 

asbestos analyzed by transmission electron microscopy 

(TEM) for fire fighters and decontamination employees during 

a prescribed burn

Job Title Task Number and 

type of fiber 

detected by 

TEM

Fire fighter #8 Fire line construction 0 

 Burn 0 

 Mop-up (dry) 0 

Fire fighter #9 Fire line construction 1 (Tremolite)

 Burn 0 

 Mop-up (dry) 0 

Fire fighter #10 Travel to burn site 0 

 Fire line construction 0 

 Burn 0 

 Mop-up (wet) 0 

 After decontamination 0 

Fire fighter #11 Fire line construction 1 (Tremolite)

 Burn 0 

 Mop-up (dry) 0 

 After decontamination 1 (Tremolite)

Fire fighter #12 Fire line construction 0 

 Burn 0 

 Mop-up (dry) 0 

Fire fighter #13 Fire line construction 0 

 Burn 0 

Decontamination 

employee #2

Travel to burn site 0 

 Prescribed burn* 0 

Decontamination 

employee #3

Prescribed burn* 1 (Tremolite)

*These samples spanned the entire prescribed burn, including 

fire line construction, burn, and mop-up activities.
D-1

Section D: Occupational Exposure Limits

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 preexisting 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 limits (STEL) or ceiling values. Unless otherwise noted, the STEL 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. 

• OSHA, an agency of the U.S. Department of Labor, publishes permissible exposure limits 

[29 CFR 1910 for general industry; 29 CFR 1926 for construction industry; and 29 CFR 1917 for 

maritime industry] called PELs. These legal 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 2007]. 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.

• Another set of OELs commonly used and cited in the United States include the threshold limit 

values or TLVs, which are recommended by ACGIH. The ACGIH TLVs are developed by 

committee members of this professional organization from a review of the published, peerreviewed literature. TLVs are not consensus standards. They are considered voluntary exposure 

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

control of health hazards” [ACGIH 2019].
D-2

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 

https://www.dguv.de/ifa/gestis/gestis-stoffdatenbank/index-2.jsp, contains international limits for 

more than 2,000 hazardous substances and is updated periodically. 

OSHA (Public Law 91-596) 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. 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.

Asbestos

Asbestos is a commercial name that includes 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. Chrysotile accounts for more than 99% of the world’s 

mined asbestos [USGS 2019]. 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 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. The OSHA 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 
D-3

cleavage fragments. PCM, the analytical method routinely used for characterizing airborne exposures, is 

incapable of differentiating these non-asbestiform 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 non-asbestiform 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 micrometers. 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 

indicate 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. 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 mine, transporting 

ore and waste rock, milling operations, and shipping the final product [Meeker et al. 2003].

Health Effects

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 
D-4

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 employees 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 employees 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; Larson et al. 2010; Peipins et al. 2003; 

Sullivan 2007].

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 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].
E-1

Section E: References 

Asbestos

Meeker GP, Bern AM, Brownfield IK, Lowers HA, Sutley SJ, Hoeffen TM, Vance JS [2003]. The 

composition and morphology of amphiboles from the Rainy Creek Complex, near Libby, Montana. Am 

Mineral 88(11–12):1955–1969, https://doi.org/10.2138/am-2003-11-1239. 

NIOSH [1976]. Revised recommended asbestos standard. Cincinnati, OH: U.S. Department of Health, 

Education, and Welfare, Center for Disease Control, National Institute for Occupational Safety and 

Health, DHEW (NIOSH) Publication No. 77-169, https://doi.org/10.26616/nioshpub77169. 

NIOSH [1984]. NIOSH testimony to the U.S. Department of Labor: statement of the National 

Institute for Occupational Safety and Health. Presented at the public hearing on occupational exposure 

to asbestos, June 21, 1984. NIOSH policy statements. Cincinnati, OH: U.S. Department of Health and 

Human Services, Centers for Disease Control, National Institute for Occupational Safety and Health. 

NIOSH [1990a]. Comments of the National Institute for Occupational Safety and Health on the 

Occupational Safety and Health Administration’s notice of proposed rulemaking on occupational 

exposure to asbestos, tremolite, anthophyllite, and actinolite, April 9, 1990, OSHA Docket No. H-033d. 

NIOSH policy statements. U.S. Department of Health and Human Services, Centers for Disease 

Control, National Institute for Occupational Safety and Health. 

NIOSH [1990b]. Testimony of the National Institute for Occupational Safety and Health on the 

Occupational Safety and Health Administration’s notice of proposed rulemaking on occupational 

exposure to asbestos, tremolite, anthophyllite, and actinolite, May 9, 1990, OSHA Docket No. H-033d. 

NIOSH policy statements. U.S. Department of Health and Human Services, Centers for Disease 

Control, National Institute for Occupational Safety and Health.

NIOSH [2011]. Current intelligence bulletin 62: asbestos fibers and other elongate mineral particles; 

state of the science and roadmap for research, revised edition. Cincinnati, OH: U.S. Department of 

Health and Human Services, Centers for Disease Control and Prevention, National Institute for 

Occupational Safety and Health, DHHS (NIOSH) Publication No. 2011-159, 

https://doi.org/10.26616/nioshpub2011159. 

USGS [2019]. Mineral commodity summaries. United States Geological Survey, 

https://www.usgs.gov/centers/nmic/mineral-commodity-summaries. 

Health Effects

Amandus HE, Wheeler R [1987]. The morbidity and mortality of vermiculite miners and millers 

exposed to tremolite-actinolite: part II. Mortality. Am J Ind Med 11(1):15–26, 

https://doi.org/10.1002/ajim.4700110103. 

Amandus HE, Wheeler PE, Jankovic J, Tucker J [1987]. The morbidity and mortality of vermiculite 

miners and millers exposed to tremolite-actinolite: part I. Exposure estimates. Am J Ind Med 11(1):1–

14, https://doi.org/10.1002/ajim.4700110102. 
E-2

ATSDR [2001]. Toxicological profile for asbestos. U.S. Department of Health and Human Services, 

Agency for Toxic Substances and Disease Registry, https://www.atsdr.cdc.gov/toxprofiles/tp61.pdf. 

IOM [2006]. Asbestos: selected cancers. Washington, DC: Institute of Medicine. The National 

Academies Press, https://doi.org/10.17226/11665. 

Larson TC, Meyer CA, Kapil V, Gurney JW, Tarver RD, Black CB, Lockey JE [2010]. Workers with 

Libby amphibole exposure: retrospective identification and progression of radiographic changes. Radiol 

255(3):924–933, https://doi.org/10.1148/radiol.10091447. 

Peipins LA, Lewin M, Campolucci S, Lybarger JA, Miller A, Middleton D, Weis C, Spence M, Black B, 

Kapil V [2003]. Radiographic abnormalities and exposure to asbestos-contaminated vermiculite in the 

community of Libby, Montana, USA. Environ Health Perspect 111(14):1753–1759, 

https://doi.org/10.1289/ehp.6346. 

Sullivan PA [2007]. Vermiculite, respiratory disease, and asbestos exposure in Libby, Montana: update 

of a cohort mortality study. Environ Health Perspect 115(4):579–585, 

https://doi.org/10.1289/ehp.9481. 

Occupational Exposure Limits 

ACGIH [2019]. 2019 TLVs and BEIs: threshold limit values for chemical substances and physical 

agents and biological exposure indices. Cincinnati, OH: American Conference of Governmental 

Industrial Hygienists, https://www.acgih.org/tlv-bei-guidelines/policies-procedurespresentations/overview. 

CFR [2019]. Code of Federal Regulations. Washington, DC: U.S. Government Printing Office, Office 

of the Federal Register, https://www.ecfr.gov/cgi-bin/ECFR?page=browse. 

NIOSH [2007]. NIOSH pocket guide to chemical hazards. Cincinnati, OH: U.S. Department of Health 

and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational 

Safety and Health, DHHS (NIOSH) Publication No. 2005-149, http://www.cdc.gov/niosh/npg/. 
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