PROPER USE OF ROOFING ASPHALTS
Fumes From Roofing Asphalts: Safety Information
What are Asphalt Fumes?
Asphalt is an extremely complex mixture of petroleum compounds. Some asphalt occurs in natural deposits in the earth. However, today nearly all asphalt is made by processing crude oils in petroleum refineries. When asphalt is heated, some of the asphalt turns into vapor and escapes into the air. When it mixes with the cooler air above a roofing kettle or tanker, some of the vapor cools back into liquid and forms a cloud of tiny droplets. Fumes are actually tiny droplets of airborne liquid asphalt. Exposure occurs when these droplets are inhaled or land on a person's skin.
Asphalt is used in a variety of roofing-related products, including shingles, built-up roofing and modified roofing felts, some single-ply membranes and flashing materials. Many of these products do not generate fumes in the field because they are not heated. Asphalt is also used in roof coatings, mastics and cements; these products release vapors that are different from asphalt fumes as they come from the petroleum solvent and not from the asphalt itself.
Asphalt fumes are created during the installation of hot-applied built-up roof systems as well as some modified bitumen and single-ply roofing membranes. Asphalt fumes are not created during the removal of these systems because the asphalt is not heated during a removal operation. As with any tear-off operation, particulates (dust) may become airborne, but there is no evidence that asphalt particulates pose a health risk to workers, beyond the possible effects of over-exposure to any general "nuisance" dust.
Among the most serious hazards facing a roofing crew is the risk of getting burned by hot asphalt. Skin contact with hot asphalt, which may be heated in excess of 400° F, can lead to very serious burns.
Fumes from asphalt can cause irritation of the eyes and mucous membranes of the nose and throat. Exposure to asphalt fumes may give some people headaches or make them nauseated. All of these effects typically go away once the person is no longer exposed to the fumes, and pose no known long-term health consequences.
Some scientists and advisory bodies, however, have expressed concern about whether exposure to asphalt fumes may pose a cancer risk to workers. Nonetheless, when all the evidence available today is considered as a whole, the prevailing view is that although the possibility of a cancer hazard cannot be ruled out scientifically, the current information is insufficient to conclude that asphalt fumes pose a cancer hazard to those who may be exposed to them. Several widely-respected scientific advisory bodies have concluded that asphalt fumes cannot be classified as a human carcinogen, and recently the National Institute for Occupational Safety and Health (NIOSH), while concluding that fumes from roofing asphalts are "possible occupational carcinogens," suggests that additional studies be conducted to "better characterize occupational exposures to asphalt fumes, vapors, and aerosols, and to further evaluate the risk of chronic disease, including lung cancer."
The NIOSH report recommends that workers using hot roofing asphalts have an exposure limit of 5.0 milligrams per cubic meter of air over any 15-minute time period. Because there is no available method of measuring total particulate exposure over a 15-minute period, there are no data available that indicate whether current exposures adhere to the REL.
Reducing Exposures to Asphalt Fumes
Because exposure to fumes from roofing asphalt can be an irritant for some people, as a professional roofer, you and the contractor must find the best ways to reduce the possibility of any discomfort for you and fellow roofers. There are several things that you and your contractor can do:
- Be sure that all points of air intake into the building are closed to the extent possible.
- Whenever possible, keep the asphalt heating equipment away from building intakes, and in an area that is acceptable for all parties in the roofing project. Restrict access to the equipment from anyone except professional roofers.
- Keep lids and covers on containers of hot asphalt (especially kettles) closed whenever possible.
- Use insulated pipes to transport hot asphalt from the ground to the roof, so that the temperature required to heat the asphalt can be kept to a minimum.
- Consider the use of kettles with engineering controls to reduce fume emission, or the use of fume recovery equipment.
- When feasible, consider the use of low-fuming asphalts.
- Have a trained and skilled crew that is experienced in working with hot asphalt.