Evaluation of Isocyanate 

Exposure during 

Polyurethane Foam 

Application and Silica 

Exposure during Rock 

Dusting at an Underground 

Coal Mine 

Kenneth W. Fent, PhD

Chad H. Dowell, MS, CIH

Health Hazard Evaluation Report

HETA 2009-0085-3107

Consolidation Coal Company

Blacksville, West Virginia

April 2010

Department of Health and Human Services

Centers for Disease Control and Prevention

Workplace

Safety and Health

 National Institute for Occupational 

Safety and Health

This Health Hazard Evaluation (HHE) report and any recommendations made herein are for the specific 

facility evaluated and may not be universally applicable. Any recommendations made are not to be 

considered as final statements of NIOSH policy or of any agency or individual involved. Additional HHE 

reports are available at http://www.cdc.gov/niosh/hhe/
The employer shall post a copy of this report 

for a period of 30 calendar days at or near 

the workplace(s) of affected employees. The 

employer shall take steps to insure that the 

posted determinations are not altered, defaced, 

or covered by other material during such 

period. [37 FR 23640, November 7, 1972, as 

amended at 45 FR 2653, January 14, 1980].
Health Hazard Evaluation Report 2009-0085-3107 Page i

Appendix A

Report Abbreviations.......................................................................ii

Highlights of the NIOSH Health Hazard Evaluation............ iii

Summary .............................................................................v

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

Assessment.........................................................................3

Results & Dicussion.............................................................4

Conclusions.........................................................................8

Recommendations...............................................................9

References ........................................................................12

Contents

Occupational Exposure Limits and Health Effects.............14

Acknowledgments Acknowledgments and Availability of Report.....................19
Page ii Health Hazard Evaluation Report 2009-0085-3107

μg/m3 Micrograms per cubic meter

ACGIH® American Conference of Governmental Industrial Hygienists

APF Assigned protection factor

CFR Code of Federal Regulations

HHE Health hazard evaluation

IARC International Agency for Research on Cancer

MDC Minimum detectable concentration

MDI Methylene diphenyl isocyanate

mmHg Millimeters of mercury

MQC Minimum quantifiable concentration

MSHA Mine Safety and Health Administration

NAICS North American Industry Classification System

ND Nondetectable

NIOSH National Institute for Occupational Safety and Health

OEL Occupational exposure limit

OSHA Occupational Safety and Health Administration

PAPR Powered air purifying respirator

PBZ Personal breathing zone

PEL Permissible exposure limit

PPE Personal protective equipment

PVC Polyvinyl chloride

REL Recommended exposure limit

STEL Short-term exposure limit

TLV® Threshold limit value

TWA Time-weighted average

WEEL Workplace environmental exposure level

Abbreviations
Health Hazard Evaluation Report 2009-0085-3107 Page iii

Highlights of the

NIOSH Health

Hazard Evaluation

The National Institute for 

Occupational Safety and 

Health (NIOSH) received 

a request for a health 

hazard evaluation (HHE) 

from the United Mine 

Workers of America, 

Local 1702. The request 

concerned potential 

methylene diphenyl 

isocyanate (MDI) exposure 

during the application 

of polyurethane foam 

and silica and asbestos 

exposures during 

rock dusting at the 

Consolidation Coal 

Company Blacksville #2 

Mine in Blacksville, West 

Virginia. 

What NIOSH Did

● We evaluated the mine on March 31, 2009, and September 

14–17, 2009.

● We watched employees apply polyurethane foam and spray 

rock dust.

● We tested the surface of the foam applicator gun to see if it 

was contaminated with MDI. 

● We took samples of the rock dust and analyzed them for 

silica and asbestos. 

● We monitored the rock duster’s breathing zone air for 

respirable silica and dust.

What NIOSH Found

● The foam applicator gun was not contaminated with MDI 

after spraying.

● The nitrile gloves the bratticeman wore while applying the 

foam protected his skin from MDI. Employees are unlikely to 

be exposed to MDI in the air. It does not readily evaporate at 

room temperature, and the foam was not aerosolized during 

application.

● We did not find asbestos in the rock dust, but we did find 

silica. The rock dusters’ exposures to silica were below 

applicable exposure limits. However, statistical analysis 

showed that rock dusters are likely overexposed to silica some 

of the time.

● The bratticeman wore an appropriate respirator during foam 

application. The rock dusters wore appropriate respirators 

during most rock dusting activities. However, the mine did 

not have a written respiratory protection plan.

What Managers Can Do

● Continue to require bratticemen to wear nitrile gloves while 

applying polyurethane foam. Ensure that airflow in the mine 

carries rock dust away from the rock dusters.

● Require the use of respirators during rock dusting that are 

at least as protective as half-mask N95 filtering facepiece 

respirators. 

● Implement a written respiratory protection program. The 

program should include medical evaluations, respirator fit 

testing, and periodic air monitoring. 
Page iv Health Hazard Evaluation Report 2009-0085-3107

Highlights of the

NIOSH Health

Hazard Evaluation

(continued)

What Employees Can Do

● Follow the Blacksville #2 Mine “Safe Work Instructions.” 

● Wear nitrile gloves while applying polyurethane foam, and 

discard these gloves after each use. Once leather gloves are 

used for foam application, they should not be used for other 

processes or worn over bare skin. 

● Tell management about any health and safety concerns you 

may have. 

● Take part in the labor-management health and safety 

committee.
Health Hazard Evaluation Report 2009-0085-3107 Page v

NIOSH received a request for an HHE from the United Mine 

Workers of America, Local 1702 representing employees at the 

Consolidation Coal Company Blacksville #2 Mine in Blacksville, 

West Virginia. The HHE request concerned potential exposure to 

MDI during the application of polyurethane foam and exposure to 

silica and asbestos during rock dusting.

In an initial evaluation on March 31, 2009, we sampled the surface 

of the foam applicator gun for MDI contamination and collected 

bulk samples of the rock dust for silica and asbestos analysis. 

During a second evaluation on September 14–17, 2009, we 

collected PBZ air samples on day-shift rock dusters for respirable 

silica and dust. 

We did not detect MDI on the surface of the foam applicator 

gun. The bratticeman who applied the foam wore nitrile gloves 

that protected his skin from MDI. Inhalation exposure to MDI is 

unlikely because the foam was not aerosolized during application 

and does not readily evaporate due to its low vapor pressure. 

Low levels of silica were found in bulk samples of rock dust. 

Asbestos was not present in the rock dust. The PBZ air 

concentrations of respirable silica were below applicable OELs. 

However, according to a statistical analysis, there is a 73% 

probability that the rock dusters’ PBZ concentrations may exceed 

the ACGIH TLV 5% of the time. 

Because of the potential for overexposure to respirable silica, we 

recommend continued use of N95 filtering facepiece respirators. 

Additionally, the company should implement a written respiratory 

protection program that incorporates medical evaluations and 

respirator fit testing. 

Keywords: NAICS 212112 (Bituminous Coal Underground Mining), 

silica, asbestos, calcium carbonate, isocyanates, MDI, rock dust, 

polyurethane foam, respirable dust

Summary

We found no evidence 

that the skin of the 

bratticemen was 

exposed to MDI during 

polyurethane foam 

application. The rock 

dusters’ silica exposures 

we measured in air were 

below OELs. However, 

statistical analysis 

showed they are likely 

overexposed to silica 

some of the time. We 

recommended that 

bratticemen wear nitrile 

gloves, that rock dusters 

wear respirators at least 

as protective as half-mask 

N95 filtering facepiece 

respirators, and that rock 

dust be applied in wellventilated areas. The mine 

should also implement 

a written respiratory 

protection program that 

incorporates medical 

evaluations and respirator 

fit testing. 
This page intentionally left blank.
Health Hazard Evaluation Report 2009-0085-3107 Page 1

Introduction

On February 6, 2009, NIOSH received a request for an HHE from 

the United Mine Workers of America, Local 1702. The request 

concerned potential isocyanate exposures during polyurethane 

foam application and potential silica and asbestos exposures during 

rock dusting at the Consolidation Coal Company, Blacksville 

#2 Mine. On March 31, 2009, and September 14–17, 2009, we 

evaluated employee exposures to isocyanates, silica, dust, and 

asbestos.

Process Description

The Blacksville #2 Mine is a longwall bituminous coal mine 

between 500 and 900 feet underground. The mine opened in 

1969, and approximately 10 square miles have been mined. 

Outdoor air is drawn into the mine using nine exhaust fans 

situated at various locations throughout the mine. At the time 

of the evaluation, 560 employees worked at the mine over three 

shifts. We evaluated two processes in the Blacksville #2 Mine, the 

application of polyurethane foam and rock dusting. 

Bratticemen apply polyurethane foam to steel ventilation stoppings 

that block and direct airflow throughout the mine (Figure 1). 

The foam consists of Component A, containing monomeric 

and polymeric MDI, and Component B, containing a mixture 

of polyols. When Components A and B mix in the nozzle of 

the foam applicator gun, the MDI and polyols react rapidly to 

form polyurethane foam. The foam dries to touch in less than a 

minute and provides an impervious air seal. After application, the 

disposable nozzle is discarded, and petroleum jelly is applied to the 

gun face and valve stems before the applicator gun is stored. 
Page 2 Health Hazard Evaluation Report 2009-0085-3107

Introduction 

(continued)

Two rock dusters work each shift. One rock duster (called the pod 

operator) regulates the air pressure at the generator attached to the 

storage pods while the other (called the hose operator) aims the 

pressurized hose and applies the rock dust to the mine surfaces. 

The rock dusters we evaluated traded duties each day. Rock dust, 

which is primarily calcium carbonate, is applied to the surfaces 

of the mine to reduce the fraction of combustible material in the 

mine (Figure 2). 

Figure 2. Spraying rock dust onto the surfaces inside the coal mine.

Figure 1. Applying polyurethane foam to a steel ventilation stopping.
Health Hazard Evaluation Report 2009-0085-3107 Page 3

Assessment

First Evaluation

We did not do air sampling for MDI because aerosols were not 

generated during the foaming process, and the evaporation of MDI 

is minimal because of its low vapor pressure (5.4 x 10–6 mmHg at 

68°F) [American Plastics Council 1999]. However, we believed that 

dermal exposure could result from MDI-contaminated equipment 

or unreacted foam coming into contact with unprotected skin. To 

evaluate dermal exposure, we sampled the surface of the gun for 

aromatic isocyanate contamination using Surface SwypesTM (SKC 

Inc., Eighty Four, Pennsylvania) wipe samples. The foam applicator 

gun was sprayed with a developer solution and then wiped with 

a Surface Swype. A second Surface Swype was wiped across the 

tip of the foam applicator gun where foam material was present 

(a positive control). A color change to orange or red indicates the 

presence of aromatic isocyanates.

We collected bulk samples of the rock dust from the storage pods 

in the mine with a metal spatula and 40-milliliter plastic vials. 

Two samples each were collected from the storage pods. Half of 

each sample was analyzed for asbestos using NIOSH Method 9002 

[NIOSH 1994]; the other half of each sample was analyzed for silica 

(specifically quartz) using MSHA Method P-7 [MSHA 1994]. 

Second Evaluation 

Over 3 days, we collected six full-shift PBZ air samples (three 

from each day-shift rock duster) for respirable dust and silica. 

Air samples were collected with 37-millimeter sampling cassettes 

containing preweighed 5-micrometer pore size PVC filters. The 

filter cassettes were attached to Dorr-Oliver nylon cyclones. 

AirCheck 2000 pumps (SKC Inc., Eighty Four, Pennsylvania) were 

used to draw 1.7 liters per minute of air through the sampling 

media. The Dorr-Oliver nylon cyclones are designed to remove 

larger particles from the sampled airstream so that the PVC filters 

collect particles in the size range representative of particles that 

deposit in the human respiratory tract (i.e., respirable particles). 

The PVC filters were analyzed for respirable dust using NIOSH 

Method 0600 [NIOSH 1994] and respirable silica using NIOSH 

Method 7500 [NIOSH 1994]. In addition, bulk samples from the 

storage pods were collected daily over the 3-day sampling period 

and analyzed for silica using NIOSH Method 7500. NIOSH 

Method 7500 is able to analyze for quartz, crystobalite, and 
Page 4 Health Hazard Evaluation Report 2009-0085-3107

Assessment (continued) tridymite. For silica analysis, both the bulk and air samples were 

pretreated for possible calcite interferences as described in NIOSH 

Method 7601 [NIOSH 1994].

Appendix A provides information about OELs and potential 

health effects of the chemicals we evaluated. Table A-1 in the 

appendix presents the OELs for respirable crystalline silica (quartz).

MDI Exposures

We found no evidence that bratticemen were exposed to MDI 

when applying polyurethane foam. The wipe sample taken on 

the handle of the foam applicator gun was negative, meaning 

that MDI was ND (< 3 to 5 micrograms/sample). Another wipe 

sample was collected to determine that the Surface Swypes were 

capable of detecting MDI. This positive control wipe sample taken 

across the tip of the foam applicator gun was positive for aromatic 

isocyanates. Thus, we have confidence that the handle of the gun 

was not contaminated with MDI. 

We reviewed the “Safe Work Instructions” for the Blacksville 

#2 Mine. According to these instructions, general dilution 

ventilation, goggles, rubber gloves, and respirators with charcoal 

filters are required for bratticemen who seal walls with foam. The 

bratticeman we observed wore light duty (< 0.30 millimeter) nitrile 

gloves under leather gloves and a North half-mask air purifying 

respirator (7700-30M) with combination organic vapor cartridges/ 

P100 particulate filters (75SCP100, North Safety Products, 

Cranston, Rhode Island). Light duty nitrile gloves have been 

shown to be effective barriers against polymeric MDI [Society of 

the Plastics Industry 1994]. Because the handle of the gun was not 

contaminated with MDI and because the bratticeman wore nitrile 

gloves when applying foam (including cleaning up and dismantling 

the foam applicator gun), dermal exposure to MDI appears to be 

well controlled. Preventing dermal exposure to MDI is important 

because dermal exposure to isocyanates can lead to skin and 

respiratory sensitization [Bello et al. 2007]. 

The combination organic vapor cartridge and P100 filter used 

with the half-mask air purifying respirator is appropriate for 

atmospheres containing MDI. These cartridges/filters should be 

Results & Dicussion
Health Hazard Evaluation Report 2009-0085-3107 Page 5

Results and Discussion (continued) changed out according to a predetermined schedule. The NIOSH 

and OSHA APF for a half-mask air purifying respirator is 10 [29 

CFR 1910.134], which means that inhalable concentrations are 

expected to be one tenth the ambient concentrations, provided 

the respirator is worn, maintained, and fitted according to OSHA 

regulations [29 CFR 1910.134]. Because MDI has a low vapor 

pressure (5.4 x 10–6 mmHg at 68°F) and the foam is injected and 

not sprayed (which could generate MDI aerosols), we expect that 

PBZ concentrations of MDI during foam application should be 

below the NIOSH REL (50 μg/m3) or ceiling limit (200 μg/m3) 

[NIOSH 2005]. Therefore, we did not do air sampling.

Asbestos, Respirable Silica, and 

Respirable Dust Exposures 

The rock dust used in the Blacksville #2 Mine is supplied by the 

Greer Lime Company (Riverton, West Virginia) and according to 

the January 2008 quality control report, is composed primarily 

of calcium carbonate (98%), but does contain other compounds 

including silica (0.75%). The bulk samples we collected did not 

contain asbestos but did contain crystalline silica (quartz) at 

levels ranging from ND (< 0.5%) to 0.98% (Table 1). For the bulk 

samples analyzed by NIOSH Method 7500, only quartz was found; 

crystobalite and tridymite were not detected.

Table 1. Percent by mass of crystalline silica (quartz) in the bulk samples of rock dust

Sample date No. of 

samples % crystalline silica Comments

3/31/2009 4 0.4

The bulk samples were collected on the same day and 

analyzed for quartz using MSHA Method P-7 [MSHA 

1994].

9/14/2009 to 

9/17/2009 3 ND (< 0.5%) to 0.94

Each bulk sample was collected on a different day and 

analyzed for quartz, crystobalite, and tridymite using 

NIOSH Method 7500 [NIOSH 1994]. Crystobalite and 

tridymite were not detected.

Table 2 provides the air sampling results for respirable dust and 

crystalline silica. The reported concentrations were time weighted 

averaged over 8 hours. The respirable dust concentrations were 

below the OELs for calcium carbonate. Because crystalline silica 

is more hazardous than calcium carbonate, the crystalline silica 

sampling results were used to determine safe levels of exposure. 
Page 6 Health Hazard Evaluation Report 2009-0085-3107

Results and Discussion (continued) Only quartz, a form of crystalline silica, was found in the air 

samples; cristobalite and tridymite (other forms of crystalline silica) 

were not detected. Respirable crystalline silica was present at PBZ 

concentrations above the MDC of 6 μg/m3 but below the MQC of 

25 μg/m3. Because the MQC is equal to the ACGIH TLV, any PBZ 

concentrations of respirable crystalline silica above the ACGIH 

TLV would have been quantifiable. Concentrations between the 

MDC and MQC are listed in Table 2 but are contained within 

parentheses to point out that there is more uncertainty associated 

with these values than with concentrations above the MQC. 

Table 2. Personal breathing zone air concentrations of respirable dust and crystalline silica for rock dusters 

measured on the second evaluation

Sample day Job duty Respirable dust* 

(μg/m3)

Respirable silica†

(μg/m3)

1

Pod operator 250 ND§

Hose operator‡ 370 (20)

2

Pod operator 430 ND§

Hose operator 1300 (13)

3

Pod operator 360 (12)

Hose operator 1500 (12)

*Respirable dust concentrations may be compared to OSHA PEL and NIOSH REL for calcium carbonate (5000 

μg/m3) [NIOSH 2005].

†

Respirable silica concentrations may be compared directly to the NIOSH REL of 50 μg/m3 [NIOSH 2005] and 

ACGIH TLV of 25 μg/m3 [ACGIH 2009]. Values in parentheses represent trace concentrations of respirable 

silica above the MDC of 6 μg/m3 but below the MQC of 25 μg/m3.

‡

The hose operator on sample day 1 was exposed to the highest percentage of silica in the respirable dust 

(5.4%). At this percentage of silica, the OSHA PEL for respirable dust is 1350 μg/m3 [NIOSH 2005], and the 

MSHA PEL is 1850 μg/m3 [30 CFR 71.1010].

§

ND = nondetectable (less than the MDC of 6 μg/m3)
Health Hazard Evaluation Report 2009-0085-3107 Page 7

Results and Discussion (continued) The sampling pump worn by the rock duster who operated the 

hose on the third sample day stopped working for 30 minutes. 

This happened during a period of time when we perceived the 

airborne dust to be at higher levels. Consequently, the reported 

PBZ concentrations of respirable dust and crystalline silica on that 

day may underestimate the actual concentrations. Furthermore, 

although the PBZ concentrations of respirable crystalline silica 

(quartz) were below applicable OELs during this evaluation (see 

Table A-1 in the appendix), we cannot be certain that rock dusters 

would not be overexposed at other times. The six air samples 

we collected may not be representative of the true exposure 

distribution (e.g., exposures over an entire year) and may not be 

sufficient to identify an overexposure.

To address the uncertainty of whether an overexposure to 

crystalline silica may exist, we statistically analyzed the data we 

collected using IHDataAnalyst V1.01 (Exposure Assessment 

Solutions Inc.) to approximate the exposure distribution and 

determine the probability of overexposure. For this analysis, 

employees were considered overexposed if the 95th percentile of 

their true exposure distribution was greater than the ACGIH TLV 

of 25 μg/m3. Hence, exceeding the ACGIH TLV more than 5% of 

the time (i.e., 5 out of 100 workdays) constitutes an overexposure. 

Maximum likelihood estimation was used for assigning values 

to the ND concentrations. According to this analysis, there is a 

73% probability that rock dusters are overexposed to respirable 

crystalline silica. Probability calculations are influenced by sample 

size and variability within the sample. A larger sample size with less 

variability leads to tighter confidence intervals and hence smaller 

probabilities of overexposure. However, collecting more air samples 

does not always result in less variability. 

We used the ACGIH TLV in our statistical analysis because the 

ACGIH TLV is more protective than the other OELs (see Table 1 

in the appendix), and according to a NIOSH health hazard review 

of occupational exposure to respirable crystalline silica [NIOSH 

2002], several epidemiologic studies have found significant risks of 

silicosis over working lifetimes at concentrations below the current 

NIOSH REL, OSHA PEL, and MSHA PEL. The ACGIH TLV is 

intended to prevent pulmonary fibrosis, which may be a risk factor 

for lung cancer [ACGIH 2006].

According to the Blacksville #2 Mine “Safe Work Instructions,” 

rock dusters are to “apply rock dust in a manner that carries 
Page 8 Health Hazard Evaluation Report 2009-0085-3107

Results and Discussion (continued) dust away from [them] and wear a respirator.” The rock dusters 

we observed wore half-mask N95 filtering facepiece respirators 

(2300N95, Moldex®, Culver City, California) during spraying. 

The NIOSH and OSHA APF for this type of respirator is 10 [29 

CFR 1910.134], which means that the inhalable concentrations 

are expected to be one tenth the ambient concentrations, provided 

the respirator is worn, maintained, and fitted according to OSHA 

regulations [29 CFR 1910.134]. Taking into account the protection 

afforded by this respirator, the probability of exceeding the ACGIH 

TLV 5% of the time becomes 0.1%. Thus, half-mask N95 filtering 

facepiece respirators should provide adequate protection from 

respirable silica exposures. On one occasion when the airflow 

was stagnant, the rock duster operating the hose wore a PAPR 

equipped with a helmet (Airstream AS-600-LBC, 3M, St. Paul, 

Minnesota) and high efficiency particulate filter (3M, AS-140-25). 

The airborne rock dust concentration appeared higher during this 

time. This type of respirator has a NIOSH and OSHA APF of 25 

[29 CFR 1910.134], and thus provides greater protection than a 

half-mask respirator. 

Although respirators are used at the Blacksville #2 Mine and 

required for certain operations including foam application and 

rock dusting, the Blacksville #2 Mine has no comprehensive 

written respiratory protection program. At the time of this 

evaluation, employees wearing respirators were not medically 

evaluated and approved to wear respirators nor were they fit-tested. 

The bratticemen applying polyurethane foam are protected from 

dermal exposures to MDI because they wear nitrile gloves and 

because the foam applicator gun was not contaminated with MDI. 

Inhalation exposures to MDI are unlikely because MDI does not 

readily evaporate at ambient temperatures in the mine, and the 

foam is not aerosolized. Asbestos was not found in bulk samples of 

the rock dust, but crystalline silica (quartz) was found. Although 

the rock dusters’ PBZ concentrations of respirable crystalline silica 

were below applicable OELs, according to a statistical analysis, 

there is a 73% probability that their PBZ concentrations may 

exceed the ACGIH TLV (25 μg/m3) 5% of the time. 

Conclusions
Health Hazard Evaluation Report 2009-0085-3107 Page 9

Based on our findings, we recommend the actions listed 

below to create a more healthful workplace. We encourage 

the Consolidation Coal Company to use a labor-management 

health and safety committee or working group to discuss the 

recommendations in this report and develop an action plan. Those 

involved in the work can best set priorities and assess the feasibility 

of our recommendations. Our recommendations are based on the 

hierarchy of controls approach discussed in the appendix. 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/or personal protective equipment 

may be needed. 

Elimination and Substitution 

Elimination or substitution of a toxic/hazardous process material 

is a highly effective means for reducing hazards. Incorporating 

this strategy into the design or development phase of a project, 

commonly referred to as “prevention through design,” is most 

effective because it reduces the need for additional controls 

in the future. Because silica is a naturally occurring mineral, 

its elimination from rock dust may not be feasible. Similarly, 

isocyanates are always used in polyurethane foams, and we are not 

aware of other types of foams that do not contain isocyanates (e.g., 

latex foams) being used in underground coal mines.

Engineering Controls 

Engineering controls reduce exposures to employees by removing 

the hazard from the process or placing a barrier between the 

hazard and the employee. Engineering controls are very effective 

at protecting employees without placing primary responsibility of 

implementation on the employee. 

1. Ensure that airflow is directed to carry rock dust particles 

away from the rock dusters. 

Recommendations
Page 10 Health Hazard Evaluation Report 2009-0085-3107

Recommendations

(continued) Administrative Controls 

Administrative controls are management-dictated work practices 

and policies to reduce or prevent exposures to workplace hazards. 

The effectiveness of administrative changes in work practices 

for controlling workplace hazards depends on management 

commitment and employee acceptance. Regular monitoring and 

reinforcement is necessary to ensure that control policies and 

procedures are not circumvented in the name of convenience or 

production.

1. Conduct periodic air monitoring to ensure that the 

respirators employees are using are sufficiently protective 

or can be eliminated once other controls are in place that 

reduce PBZ concentrations of silica to acceptable levels.

Personal Protective Equipment 

PPE is the least effective means for controlling employee exposures. 

Proper use of PPE requires a comprehensive program, and calls 

for a high level of employee involvement and commitment to be 

effective. The use of PPE requires the choice of the appropriate 

equipment to reduce the hazard and the development of 

supporting programs such as training, change-out schedules, and 

medical assessment if needed. PPE should not be relied upon as 

the sole method for limiting employee exposures. Rather, PPE 

should be used until engineering and administrative controls can 

be demonstrated to be effective in limiting exposures to acceptable 

levels.

1. Continue to require that bratticemen wear nitrile gloves 

when applying polyurethane foam. The nitrile gloves 

should be discarded after each foam application (which 

includes cleaning up and dismantling the foam applicator 

gun) to prevent cross contamination. Metatarsal leather 

gloves can be worn over the nitrile gloves. However, to 

prevent cross contamination, the leather gloves should 

not be worn over bare hands or be used for other work 

processes. This procedure should be clearly stated in the 

“Safe Work Instructions.” Chapter 9 of the MSHA Coal 

Mine Health Inspection Procedures Handbook provides 

more information on protecting employees who apply 

polyurethane foam [MSHA 2003].
Health Hazard Evaluation Report 2009-0085-3107 Page 11

Recommendations

(continued) 2. Change cartridges and filters used in air purifying 

respirators according to a predetermined schedule. Refer 

to the OSHA Respiratory Protection eTool at http://www.

osha.gov/SLTC/etools/respiratory/change_schedule.html

for more information on respirator change-out schedules. 

3. Require the use of respirators that are at least as effective 

as half-mask N95 filtering facepiece respirators during rock 

dusting. These respirators, when worn and maintained 

properly, should adequately protect rock dusters from 

respirable crystalline silica exposures. Required use of 

these respirators should be clearly stated in the “Safe Work 

Instructions.” 

4. Implement a written respiratory protection program. 

According to MSHA regulations [30 CFR 56/57.5005], 

the program must meet the requirements of the American 

National Standard: Practices for Respiratory Protection 

ANSI Z88.2-1969 [ANSI 1969], which includes training on 

the proper wear and maintenance of respirators, medical 

evaluations to determine that employees are physically 

able to perform their work while wearing respirators, and 

respirator fit testing. The NIOSH Guide to Industrial 

Respiratory Protection at http://www.cdc.gov/niosh/87-

116.html and OSHA regulations [29 CFR 1910.134] provide 

additional guidance on implementing a comprehensive 

written respiratory protection program. 
Page 12 Health Hazard Evaluation Report 2009-0085-3107

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ed. Schlecht PC, O’Connor PF, eds. 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. 94-113 (August 

1994); 1st Supplement Publication 96-135, 2nd Supplement 

Publication 98-119, 3rd Supplement Publication 2003-154. [http://

www.cdc.gov/niosh/nmam].
Health Hazard Evaluation Report 2009-0085-3107 Page 13

References (continued) NIOSH [2002]. NIOSH hazard review: health effects of 

occupational exposure to respirable crystalline silica. Cincinnati, 

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

for Disease Control and Prevention, National Institute for 

Occupational Safety and Health (NIOSH) Publication No. 2002-

129.

NIOSH [2005]. NIOSH pocket guide to chemical hazards. Barsen 

ME, ed. Cincinnati, OH: U.S. Department of Health and Human 

Services, Centers for Disease Control and Prevention, National 

Institute for Occupational Safety and Health (NIOSH) Publication 

No. 2005-149.

Society of the Plastics Industry [1994]. Technical bulletin: PMDI 

user guidelines for chemical protective clothing selection. [http://

www.osha.gov/SLTC/autobody/docs/techbjul94.html]. Date 

accessed: January 2010.
Page 14 Health Hazard Evaluation Report 2009-0085-3107

In evaluating the hazards posed by workplace exposures, NIOSH investigators use both mandatory (legally 

enforceable) and recommended OELs for chemical, physical, and biological agents as a guide for making 

recommendations. OELs have been developed by Federal agencies and safety and health organizations to 

prevent the occurrence of adverse health effects from workplace exposures. Generally, OELs suggest levels 

of exposure that most employees may be exposed 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 from 

adverse health effects even if their exposures are maintained below these levels. A small percentage may 

experience adverse health effects because of individual susceptibility, a preexisting medical condition, 

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

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

employee to produce health effects even if the occupational exposures are controlled at the level set by 

the exposure limit. Also, some substances can be absorbed by direct contact with the skin and mucous 

membranes in addition to being inhaled, which contributes to the individual’s overall exposure. 

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 STEL or ceiling 

values where health effects are caused by exposures over a short period. Unless otherwise noted, the STEL 

is a 15-minute TWA exposure that should not be exceeded at any time during a workday, and the ceiling 

limit is an exposure that 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, while 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 enforceable in 

workplaces covered under the Occupational Safety and Health Act. NIOSH RELs are recommendations 

based on a critical review of the scientific and technical information available on a given hazard and the 

adequacy of methods to identify and control the hazard. NIOSH RELs can be found in the NIOSH Pocket 

Guide to Chemical Hazards [NIOSH 2005]. NIOSH also recommends different types of risk management 

practices (e.g., engineering controls, safe work practices, employee education/training, personal protective 

equipment, and exposure and medical monitoring) to minimize the risk of exposure and adverse health 

effects from these hazards. Other OELs that are commonly used and cited in the United States include 

the TLVs recommended by ACGIH, a professional organization, and the WEELs recommended by the 

American Industrial Hygiene Association, another professional organization. The TLVs and WEELs are 

developed by committee members of these associations from a review of the published, peer-reviewed 

literature. They are not consensus standards. ACGIH TLVs 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 2009]. WEELs have been established for some chemicals “when no other legal or 

authoritative limits exist” [AIHA 2009].

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

both legal and recommended limits. Since 2006, the Berufsgenossenschaftliches Institut für Arbeitsschutz 

(German Institute for Occupational Safety and Health) has maintained a database of international 

Appendix A: Occupational Exposure Limits and Health Effects
Health Hazard Evaluation Report 2009-0085-3107 Page 15

Appendix A: Occupational Exposure Limits and Health Effects (continued)

OELs from European Union member states, Canada (Québec), Japan, Switzerland, and the United 

States available at http://www.dguv.de/bgia/en/gestis/limit_values/index.jsp. The database contains 

international limits for over 1250 hazardous substances and is updated annually. 

Employers should understand that not all hazardous chemicals have specific OSHA PELs, and for some 

agents the legally enforceable and recommended limits may not reflect current health-based information. 

However, an employer is still required by OSHA to protect its employees from hazards even in the absence 

of a specific OSHA PEL. 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))]. Thus, NIOSH investigators encourage 

employers to make use of other OELs when making risk assessment and risk management decisions to 

best protect the health of their employees. NIOSH investigators also encourage the use of the traditional 

hierarchy of controls approach to eliminate or minimize identified 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) 

personal protective equipment (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 that focuses resources on exposure controls by describing how a risk 

needs to 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 the OELs, when available.

Undergound Coal Mines 

MSHA has regulatory authority in underground coal mines. Thus, exposures must be maintained below 

MSHA PELs if they exist for the compounds of interest. Some OELs are more protective or based on more 

recent scientific information than other OELs. Below we discuss all OELs pertinent to this evaluation, as 

well as the potential health effects from exposure to the chemicals we evaluated. 

Isocyanates 

Respiratory sensitization and occupational asthma are the most common adverse health outcomes 

associated with isocyanate exposure [NIOSH 1978]. Respiratory sensitization can occur at low levels of 

inhalation exposure [Chan-Yeung 1986]. Hence, the OELs for inhalation exposure to MDI are relatively 

low (e.g., NIOSH REL is 50 μg/m3) [NIOSH 2005]. Evidence suggests that dermal exposure to isocyanates 

can also lead to skin and respiratory sensitization [Bello et al. 2007]. NIOSH recommends preventing 

contact of MDI with skin [NIOSH 2005]. 
Page 16 Health Hazard Evaluation Report 2009-0085-3107

Appendix A: Occupational Exposure Limits and Health Effects (continued)

Table A-1. Occupational exposure limits for respirable crystalline silica (quartz)

OEL (μg/m3) Comments

NIOSH REL [NIOSH 2005] 50 For respirable crystalline silica.

OSHA PEL [NIOSH 2005] 10,000 / (% silica + 2) For respirable dust containing silica. Assuming 

100% silica, the OSHA PEL = 98 μg/m3.

MSHA PEL [30 CFR 71.101] 10,000 / (% silica) For respirable dust containing silica. Assuming 

100% silica, the MSHA PEL = 100 μg/m3.

ACGIH TLV [ACGIH 2009] 25 For respirable crystalline silica.

Crystalline Silica

Exposure to crystalline silica primarily affects the lungs. Long term exposure can cause pulmonary fibrosis 

(silicosis) [NIOSH 2005]. According to IARC, inhalation of silica in the form of quartz or cristobalite 

is considered carcinogenic to humans [IARC 1997], specifically leading to lung cancer. The OELs for 

respirable crystalline silica (quartz) are provided in Table A-1. 

Calcium Carbonate 

The rock dust is composed primarily of calcium carbonate. No adverse health effects have been found 

from calcium carbonate exposure [IPCS 1999]. The OSHA PEL and NIOSH REL for calcium carbonate 

are 5000 μg/m3 respirable particles [NIOSH 2005]. No specific MSHA PEL or ACGIH TLV exists for 

calcium carbonate. 

References

ACGIH [2009]. Threshold limit values for chemical substances and physical agents and biological 

exposure indices. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

AIHA [2009]. AIHA 2009 Emergency response planning guidelines (ERPG) & workplace environmental 

exposure levels (WEEL) handbook. Fairfax, VA: American Industrial Hygiene Association.

Bello D, Herrick CA, Smith TJ, Woskie SR, Streicher RP, Cullen MR, Liu Y, Redlich CA [2007]. Skin 

exposure to isocyanates: reasons for concern. Environ Health Perspect 115(3):328–335.

CFR. Code of Federal Regulations. Washington, DC: U.S. Government Printing Office, Office of the 

Federal Register.
Health Hazard Evaluation Report 2009-0085-3107 Page 17

Appendix A: Occupational Exposure Limits and Health Effects (continued)

Chan-Yeung M [1986]. Occupational asthma. Clin Rev Allergy 4(3):251–266.

IARC [1997]. Monographs on the evaluation of the carcinogenic risks to humans: silica. Vol. 68. Lyon, 

France: World Health Organization, International Agency for Research on Cancer [http://monographs.

iarc.fr/ENG/Monographs/vol68/volume68.pdf]. Date accessed: January 2010.

IPCS (WHO/International Programme on Chemical Safety) [1999]. International Chemical Safety card: 

calcium carbonate [http://www.cdc.gov/niosh/ipcsneng/neng1193.html. Date accessed: January 2010.

NIOSH [1978]. NIOSH criteria for a recommended standard: occupational exposure to diisocyanates. 

Cincinnati, OH: U.S. Department of Health, Education, and Welfare, Health Services and Mental Health 

Administration, National Institute for Occupational Safety and Health, DHEW (NIOSH).

NIOSH [2005]. 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/]. Date 

accessed: January 2010.
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Health Hazard Evaluation Report 2009-0085-3107 Page 19

Acknowledgments and

Availability of Report

The Hazard Evaluations and Technical Assistance Branch 

(HETAB) of the National Institute for Occupational Safety and 

Health (NIOSH) conducts field investigations of possible health 

hazards in the workplace. These investigations are conducted 

under the authority of Section 20(a)(6) of the Occupational Safety 

and Health Act of 1970, 29 U.S.C. 669(a)(6) which authorizes 

the Secretary of Health and Human Services, following a written 

request from any employer or authorized representative of 

employees, to determine whether any substance normally found 

in the place of employment has potentially toxic effects in such 

concentrations as used or found. HETAB also provides, upon 

request, technical and consultative assistance to federal, state, and 

local agencies; labor; industry; and other groups or individuals to 

control occupational health hazards and to prevent related trauma 

and disease.

The findings and conclusions in this report are those of the 

authors and do not necessarily represent the views of NIOSH. 

Mention of any company or product does not constitute 

endorsement by NIOSH. In addition, citations to websites 

external to NIOSH do not constitute NIOSH endorsement of 

the sponsoring organizations or their programs or products. 

Furthermore, NIOSH is not responsible for the content of these 

websites. All Web addresses referenced in this document were 

accessible as of the publication date.

This report was prepared by Kenneth W. Fent and Chad H. Dowell 

of HETAB, Division of Surveillance, Hazard Evaluations and Field 

Studies. Health communication assistance was provided by Stefanie 

Evans. Editorial assistance was provided by Ellen Galloway. 

Desktop publishing was performed by Robin Smith.

Copies of this report have been sent to employee and management 

representatives at the Consolidation Coal Company, the 

Pennsylvania Department of Health, the Occupational Safety 

and Health Administration Region 3 Office, and the Mine Safety 

and Health Administration District 2 Office. This report is not 

copyrighted and may be freely reproduced. The report may be 

viewed and printed at http://www.cdc.gov/niosh/hhe/. Copies 

may be purchased from the National Technical Information Service 

at 5825 Port Royal Road, Springfield, Virginia 22161.
NIOSH [2010]. Health hazard evaluation report: evaluation of isocyanate 

exposure during polyurethane foam application and silica exposure 

during rock dusting at an underground coal mine, Blacksville, WV. By Fent 

KW, Dowell CH. Cincinnati, OH: U.S. Department of Health and Human 

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

Occupational Safety and Health, NIOSH HETA No. 2009-0085-3107.

To receive NIOSH documents or information about 

occupational safety and health topics, contact NIOSH at:

1-800-CDC-INFO (1-800-232-4636)

TTY: 1-888-232-6348

E-mail: cdcinfo@cdc.gov

or visit the NIOSH web site at: www.cdc.gov/niosh.

For a monthly update on news at NIOSH, subscribe to 

NIOSH eNews by visiting www.cdc.gov/niosh/eNews.

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