Background

2.1 Number of Workers Potentially Exposed

About 3,600 hot-mix asphalt facilities and 7,000 paving contractors employ nearly 300,000 workers in the United States [Asphalt Paving Environmental Council (APEC) 1999]. Currently, the industry estimates that about 50,000 on-roof workers are exposed to asphalt fumes during, on the average, 40% of their working hours. Approximately 1,500 to 2,000 employees are exposed to asphalt fumes in approximately 100 roofing manufacturing plants [Asphalt Roofing Environmental Council (AREC) 1999].

2.2 Uses

Asphalt is commercially valuable because of its adhesive properties, flexibility, durability, water resistance, and ability to form strong cohesive mixtures with mineral aggregates. Most of the asphalt produced in the United States is used in paving and roofing. Only about 1% is used for other purposes, such as waterproofing, damp-proofing, insulation, and paints [Asphalt Institute (AI) 1990a]. Of the three types of asphalt products (asphalt paving cements, cutback asphalts, and asphalt emulsions) applied in U.S. paving operations, asphalt paving cements account for 85% of the total. Cutback asphalts and asphalt emulsions for road sealing and maintenance account for 4% and 11%, respectively, of the total [AI 1990a].

There are three basic grades of roofing asphalt.

• Saturant grade asphalt, a nonoxidized "straight reduced" asphalt or asphalt flux (typically an AC–10 or AC–20 grade material) used to manufacture saturated organic felt plies for built-up-roof (BUR) systems, organic felt shingles, and other roofing materials such as roll roofing.
• Coating grade asphalt, an oxidized asphalt used to manufacture roofing materials for a variety of roofing systems, such as asphalt shingles, polymer-modified bitumen roofing, felts, and roll roofing products.
• Mopping grade asphalt, an end-product that is melted and used in the construction of BUR systems and some modified bitumen systems. In the United States, mopping-grade roofing asphalts are classified into four types on the basis of their softening point temperature and resistance to flow (Table 2–1). The specific type applied to a roof is determined by roof grade or slope. Type I roofing asphalt, often referred to as “dead level,” has a low softening point and is applied on surfaces having a grade of 0.5 inches per foot (in/ft) or less. Types II and III are typically applied on roofs having slopes of 0.5 to 1.5 and 1 to 3 in/ft, respectively. Type IV (a hard asphalt with a high softening point) is applied on roofs with a grade of 2 to 6 in/ft [American Society for Testing Materials (ASTM) 1997]. For further information, see section 3.2.2.2.

Each of these three grades of asphalt— saturant, coating, or mopping—is also used in the manufacture of a variety of miscellaneous asphalt roof coating and sealant products. Asphalt roofing shingles, roll goods, underlayment felts, and roof coatings, cements, and mastics do not require heating during installation, and therefore workers are not exposed to asphalt fumes.

Information on asphalt-based paints can be found in section 3.2.3. Additional uses and applications of asphalt are provided in Appendix A.