Asphalt Fumes

Asphalt

Asphalt, otherwise known as Bitumen, is a dark brown to black material with cement like qualities made by refining petroleum crude oils. Asphalt is not a single chemical substance, but a complex mixture containing thousands of different substances, many of them complex organic compounds that are difficult or impossible to identify individually with available analytical techniques. The chemical composition of crude oil varies greatly, and a variety of different refining processes are used to make asphalts that meet the performance specifications and physical properties required for different end-uses. As a result of the complexity and variability of their composition, no two asphalts are exactly the same, and the specific chemical structure of any one asphalt cannot be completely defined.

There are two main types of asphalt, straight run asphalt and air blown or oxidized asphalt. Straight run asphalt is used for paving roads, airport runways, and parking lots. It comes in a solid form so it must first be cut with a solvent to bring it to a more liquid state. This is known as cut back asphalt. Highway workers are most likely to use straight run asphalt. Air blown asphalt has a high softening point and is used primarily in roofing, pipe covering, and similar situations.

Asphalt Fumes

When asphalt is heated, a small portion of it is released as a vapor. When the vapors cool in the air, some of them turn into a cloud of tiny droplets called “fume”. Not every compound that is part of the asphalt becomes part of the fume that is created when asphalt is heated. Only the chemicals that are more volatile become part of the fume. It has been estimated that only about 0.0001 % of the base asphalt evolves into fume. Fumes contain very small, solid, airborne particles which are easily inhaled by the worker. Inhalation of asphalt fumes can cause irritation to the nose, throat, and lungs. Fumes may also contain hydrogen sulfide vapors, which are very toxic, as well as the vapors generated by the solvents used to "cut" the asphalt. Exposure to sunlight or other ultraviolet light may make these skin conditions worse.

Short-Term (Acute) Health Effects

The only known health effects of exposure to asphalt fumes for short periods of time (that is, for a few minutes or hours) are irritation of the eyes and upper respiratory tract (i.e., the nose and throat). Irritation, if it does occur, is usually mild and temporary. Several types of skin irritation have also been reported among some asphalt workers. Some asphalt workers have also experienced headache, nausea, decreased appetite and fatigue, although the role of asphalt fumes in causing such nonspecific symptoms has not been established.

Long Term Health Effects

Chronic (long term) Health Effects of Asphalt fumes can causes rashes and other skin conditions, possibly including skin cancers. In addition, asphalt particles left on the hands may accidentally get into the eyes causing severe irritation to the eyes. Hot asphalt may also cause severe burns if splashed onto exposed skin.

Asphalt fumes contain trace quantities of substances called poly-nuclear aromatic compounds (PACs). Some of these chemicals are considered suspect carcinogens because they have caused tumors in studies on laboratory animals. However, because of limited analytical techniques for detecting specific PAC materials like asphalt fumes, the existing evidence does not reliably show that the PACs in asphalt fumes include carcinogenic substances. Even if low levels of potentially carcinogenic PACs are in fact present in asphalt fumes, the National Institute for Occupational Safety and Health (NIOSH) has determined that such a finding, by itself, would not warrant a conclusion that asphalt fumes pose a cancer hazard to exposed humans.

Recommended Exposure Limits For Workers To Asphalt Fumes

There is no legal standard specifically limiting worker exposure to asphalt fumes in the U.S. In 1992, OSHA proposed a permissible exposure limit (PEL) of 5 milligrams per cubic meter of air (5.0 mg/m3) to protect against potential irritation effects. Final decision this proposal was suspended due to an intervening court decision, and OSHA has not scheduled any further action. No consensus has happened on an appropriate and protective limit on worker exposures to asphalt fumes, in part because the existing recommendations are inconsistent with respect to both the numerical limit on exposure and the method for measuring exposure. The pending OSHA proposal of 5.0 mg/m3, for example, measures exposure as a time-weighted average of “total particulate” collected over an eight-hour shift. Yet, NIOSH’s recent Hazard Review continues in effect the existing NIOSH Recommended Exposure Limit (REL) of 5.0 mg/m3, measured as total particulate. Like OSHA’s proposed PEL, the NIOSH REL is intended to protect against irritation effects. However, unlike the OSHA proposal, the REL is measured as a 15-minute ceiling concentration.

The ACGIH, American Conference of Governmental Industrial Hygienists, revised its recommended “threshold limit value” (TLV) for asphalt fumes to 0.5 mg/m3, measured as the time-weighted average of “benzene-extractable inhalable particulate” over a full work shift, to prevent irritation effects. At the present time, it is believed that average exposures in asphalt manufacturing operations are generally near or below the new TLV. The same conditions apply in many hot asphalt application operations, although it is known that higher exposures can occur in these operations when poor work practices such as overheating the asphalt are used.

An authoritative review of these studies was performed in 1994 by the International Agency for Research on Cancer (IARC) , whose evaluations of the cancer-causing properties of industrial substances often form the basis for regulatory action in the United States. Although there were excess cancer rates in asphalt workers, IARC found that there were serious limitations in the designs of these studies, and that the cancer risk seen in these studies might be the result of exposure to other materials, particularly known carcinogens such as coal tar, asbestos, and tobacco smoking. IARC determined, accordingly, that the studies in humans provide no adequate basis to conclude that exposure to asphalt fumes poses a cancer hazard.

Possible Long Term Health Effects Of Asphalt Fumes

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