DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Reducing Worker Exposure to Asphalt 

Fumes from Roofing Kettles

2003]. The extent to which these 

findings may be caused by asphalt 

fume exposure is unknown. Asphalt fumes have been reported 

to cause coughing and headaches 

and to irritate the mucous membranes of the eyes, nose, and respiratory tract. Observations of 

acute irritation in workers from 

airborne and dermal exposures 

to asphalt fumes and aerosols and 

the potential for chronic health 

effects, including cancer, warrant 

continued diligence in the control 

of exposures [NIOSH 2001].

In 2003, NIOSH published a technical report on current practices 

used to reduce exposure during the 

application of hot asphalt to roofs. 

Two control methods identified for 

further evaluation were (1) substituting fume-suppressing asphalt 

for conventional asphalt and (2) using afterburner and loader systems 

to reduce asphalt-fume emissions. 

NIOSH conducted field studies to 

evaluate the effectiveness of these 

engineering controls. 

Surveys were conducted during the construction of built-up 

roof (BUR) systems, which account for approximately 14% of 

the new retrofit markets for lowslope roofs [NRCA 2003]. BUR 

systems are layers or plies of organic (e.g., cellulose), fiberglass 

or polyester felt sealed together 

with hot asphalt heated in kettles 

(see Figure 1). The layers protect 

against moisture penetration and, 

combined with the sealing ability of asphalt, make BUR systems 

excellent for waterproofing flat or 

low-sloped roofs. On-roof workers such as those who apply the 

hot asphalt to the felt plies are 

exposed to asphalt fumes. Kettle operators are exposed to the 

highest concentrations of fumes 

on most BUR jobs.

Asphalt roofing kettles normally 

consist of a round-bottomed steel 

vessel with a heating unit composed of propane-fired burners. 

The kettles come in capacities of 

25 to 1,500 gallons. Kettle operators maintain the appropriate 

Description of

Exposure

An estimated 46,000 roofing contractors work in the United States. 

These contractors are primarily small businesses that specialize in residential roofing [NRCA 

2000]. Approximately 50,000 onroof workers are exposed to asphalt fumes [AREC 1999].

Studies of roofers show an excess 

of lung, bladder, brain, liver, and 

digestive system cancers among 

roofers and workers in other 

occupations with the potential 

for exposure to asphalt [NIOSH 

Summary

Roofers, particularly kettle operators, may be exposed to asphalt fumes when asphalt is 

heated in roofing kettles for 

built-up roof construction. Asphalt fumes have been associated with a number of health 

risks. NIOSH examined two 

engineering controls for reducing exposure to asphalt fumes: 

fume-suppressing asphalt and 

afterburner and loader systems. 
supply of hot asphalt at the correct temperature for 

application on the roof during construction of BURs 

(see Figure 2). The type of asphalt used and the 

application temperature vary depending on factors 

such as the slope of the roof being built. 

Control

Fume-Suppressing Asphalt

Fume-suppressing asphalt (also known as low-fuming 

asphalt) contains a small amount of a polymer that, 

when heated, floats to the surface creating a skim layer on the asphalt in the kettle. This layer may reduce 

the emission of asphalt fumes from the kettle. Between 1999 and 2001, NIOSH conducted four evaluations for controlling worker exposure to asphalt 

fumes during the use of fume-suppressing asphalt. 

The studies showed that when fume-suppressing asphalt was used, exposures to contaminants in the asphalt fumes were greatly reduced (by 70%–83%) for 

kettle operators. However, it was not certain whether exposures were reduced for roof-level workers 

who usually did not work near the kettle. 

Afterburner and Loader Systems

Afterburner systems reduce the amount of fumes 

emitted and reduce worker exposures by burning 

asphalt fumes from the surface of the asphalt in the 

kettle. This system may also be used with loading 

devices that allow the kettle operator to add asphalt 

Figure 2. Kettle Operator. Courtesy of Thomas R. Shanahan, National Roofing Contractors Association.

Figure 1. Applying hot asphalt to fiberglass felt.

without opening the kettle lid and releasing fumes. 

During six NIOSH field studies, the afterburner and 

loader systems may have reduced the kettle operators’ exposures to asphalt fumes, but variables such 

as work practices made it difficult to interpret the 

results. When conditions were well controlled, the 

contaminants were reduced by 73%–88%. Experience has shown that any afterburner and/or loader 

system must be carefully designed to avoid causing 

ignition of asphalt fumes and explosions or fires in 

the kettle or kettle area.

Recommendations

The surveys showed that the way workers performed their duties greatly influenced the effectiveness of the control measures. NIOSH recommends 

the following work practices and engineering controls to reduce workers exposure to asphalt fumes. 

Asphalt and Kettle Selection

■	 Use fume-supressing asphalt instead of conventional asphalt, or kettles with afterburner and loader 

systems when feasible. Follow the manufacturers’ 

recommendations for work practices when using 

fume-suppressing asphalt. Because of safety concerns potentially associated with the use of kettle 

afterburner and/or loader systems, the manufacturers’ use, maintenance, and work practice recommendations should be strictly followed.
■	 Use kettles of appropriate size for the job. If kettles are too small, they will have to be opened 

more frequently to add asphalt, which increases 

worker exposure.

■	 Make sure the lid fits tightly. Close the lids during 

normal operations when asphalt is not being added.

■	 When opening the kettle lid to refill the kettle, fill to 

the maximum fluid level and complete other tasks 

such as skimming and taking temperature readings. 

This will reduce the number of times the lid must be 

opened.

■	 Chop the asphalt kegs into easy-to-handle pieces before opening the kettle lid to reduce the time the lid 

must be kept open when refilling.

Placing the Kettle at the Worksite

■ Set the kettle on a level area to avoid spilling or tipping the kettle.

■	 Place the kettle where the kettle operator and other 

on-roof workers will be least exposed to the fumes—

for example, downwind from the workers.

■	 Always place the kettle with the inside of the lid facing away from the building (allowing fumes to be released away from the building when the lid is open).

■	 Place the kettle away from air intake vents, doors, 

and windows to minimize the risk of exposing building occupants to asphalt fumes.

■	 Restrict access to the area immediately around 

the kettle. Mark the area with warning tape, traffic cones, and/or signs. The restricted area should be 

large enough for the kettle operator to work as well 

as reduce the exposure of other on-roof workers by 

keeping them away from the kettle.

Maintaining Asphalt Temperature in the 

Kettle

■	 Maintain the lowest possible asphalt temperature in 

the kettle within the manufacturers’ recommended temperature range. Always keep the temperature of the asphalt in the kettle at least 25 °F below 

the maximum heating temperature specified by the 

manufacturer. Recommended application temperatures and maximum heating temperatures can be 

found on keg labels or bills of lading for asphalt delivered by tanker.

■	 Before starting the job, look at all temperature-related equipment such as thermometers and automatic 

shut-off mechanisms to make sure they are in good 

working order.

■	 Calibrate the kettle thermometers and thermostats 

at least monthly or as recommended by the manufacturer.

■	 Take manual temperature readings using a stem 

thermometer inserted just below the surface of 

the asphalt.

Acknowledgments

The principal contributors to this publication were 

David A. Marlow and Jennifer L. Topmiller of the Division of Applied Research and Technology, National 

Institute for Occupational Safety and Health. John J. 

Whalen, under a contract with the Division of Federal 

Occupational Health, served as lead writer/editor.

References

AREC [1999]. Comments on the Asphalt Roofing Environmental Council on NIOSH’s September 1998 hazard review document: health effects of occupational exposure to asphalt. The 

Asphalt Institute, Asphalt Roofing Manufacturers’ Association, 

National Roofing Contractors Association, Roof Coating Manufacturers’ Association. Unpublished.

NRCA [2000]. NRCA 1999–2000 annual market survey. Rosemont, IL: National Roofing Contractors Association.

NRCA [2003]. NRCA 2002–2003 annual market survey. Rosemont, IL: National Roofing Contractors Association.

NIOSH [2001]. Hazard review: health effects of occupational exposure to asphalt. Cincinnati, OH: U.S. Department of Health 

and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2001–

110.

NIOSH [2003]. Asphalt fume exposures during the application 

of hot asphalt to roofs. Cincinnati, OH: U.S. Department of 

Health and Human Services, Public Health Service, Centers for 

Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 

2003–112.
DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

4676 Columbia Parkway

Cincinnati, OH 45226–1998

For More Information

Work practices during the use of fume-suppressing asphalt 

can be found at the following Web site: www.owenscorning.

com/trumbull/health/practices.asp.

Additional information about asphalt fume exposures during the application of hot asphalt to roofs and methods to 

control the exposures can be found in Asphalt Fume Exposures During the Application of Hot Asphalt to Roofs: Current 

Practices for Reducing Exposures, [DHHS(NIOSH) Publication No. 2003–112], (www.cdc.gov/niosh/docs/2003-112). 

For copies of the NIOSH field reports this document is based 

on, contact NIOSH at 

NIOSH

Publications Dissemination

4676 Columbia Parkway

Cincinnati, OH 45226–1998

Telephone: 1–800–35–NIOSH (1–800–356–4674)

Fax: 513–533–8573 ■ E-mail: pubstaft@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.

Mention of any company or product does not constitute endorsement by NIOSH. In addition, citations to Web sites 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 Web sites.

This document is in the public domain and may be freely copied or reprinted. NIOSH encourages all readers of 

the Workplace Solutions to make them available to all 

interested employers and workers.

As part of the Centers for Disease Control and Prevention, 

NIOSH is the Federal agency responsible for conducting research and making recommendations to prevent work-related 

illnesses and injuries. All Workplace Solutions are based on research studies that show how worker exposures to hazardous 

agents or activities can be significantly reduced.

Reducing Worker Exposure to Asphalt Fumes 

from Roofing Kettles

DHHS (NIOSH) Publication No. 2007–115

Safer • Healthier • PeopleTM February 2007