4.1 OCCUPATIONAL EXPOSURE LIMITS

Currently, no Occupational Safety and Health Administration (OSHA) standard exists for asphalt fumes. In a 1988 proposed rule on air contaminants, OSHA proposed a permissible exposure limit (PEL) of 5 mg/m3 as an 8-hr time-weighted average (TWA) for asphalt fume exposures in general industry. This proposal was based on a preliminary finding that asphalt fumes should be considered a potential carcinogen [53 Fed. Reg.* 21193]. In 1989, OSHA announced that it would delay a final decision on the 1988 proposal because of complex and conflicting issues submitted to the record [54 Fed. Reg. 2679]. In 1992, OSHA published another proposed rule for asphalt fumes that included a PEL of 5 mg/m3 (total particulates) for general industry, construction, maritime, and agriculture [57 Fed. Reg. 26182]. Although OSHA invited comment on all of the alternatives, its proposed standard for asphalt fumes would establish a PEL of 5 mg/m3 (total particulates) based on avoidance of adverse respiratory effects. The OSHA docket is closed, and OSHA has not scheduled any further action.

In a 1977 criteria document [NIOSH 1977], NIOSH established a recommended exposure limit (REL) of 5.0 mg/m3 as a 15-min ceiling limit for asphalt fumes measured as total particulates. The NIOSH REL was intended to protect workers against acute effects of exposure to asphalt fumes, including irritation of the serous membranes of the conjunctivae and the mucous membranes of the respiratory tract. In 1988, NIOSH (in testimony to the Department of Labor) recommended that asphalt fumes be considered a potential occupational carcinogen [NIOSH 1988]. In a later document [NIOSH 2000], NIOSH published a review of the health effects data available since the publication of the 1977 criteria document [NIOSH 1977]. This review is available at the NIOSH Web site (www.cdc.gov/niosh).

The current American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) for asphalt fume is 0.5 mg/m3 (benzene-soluble aerosol of the inhalable fraction) as an 8-hr TWA concentration with an A4 designation, indicating that it is not classifiable as a human carcinogen [ACGIH 2002].

4.2 EXPOSURE DURING ASPHALT ROOFING OPERATIONS

Information is limited about the extent of worker dermal and airborne exposure to asphalt fumes during the application of hot asphalt to roofs. In general, asphalt fume exposures determined from personal-breathing-zone (PBZ) samples collected at different worksites indicate that total

*Federal Register. See Fed. Reg. in references.
particulate and soluble fraction concentrations can be highly variable. Differences in reported PBZ concentrations are most likely a result of the following factors: (1) environmental conditions (wind velocity, temperature) at the worksite, (2) the type of sampling and analytical method used to collect and evaluate exposures, (3) other work tasks (e.g., tear-off of old roof) that may contribute to worker exposure, (4) the work practices used in operating the kettle and applying asphalt (e.g., location of the kettle at the worksite, frequency of opening the kettle lid, type of asphalt and asphalt temperature, the manner in which workers apply asphalt to the roof relative to the wind direction), and (5) the length of time in which the PBZ sample was collected during the work shift. Controlled studies by Franzen and Trumbore [2000] found that increasing kettle temperatures from 500 ?F (260 ?C) to 550 ?F (288 ?C) caused a dramatic twofold increase in measurements of total suspended particulates and the benzene soluble fraction. However, opacity readings, which measure the visibility of the fumes, were the same at both temperatures.

4.2.1 Airborne Exposures

Pertinent exposure results determined from PBZ samples collected from the 1970s through the 1990s are summarized below and listed in Table A–1 of Appendix A. In the 1970s, NIOSH conducted industrial hygiene studies of roofers applying hot asphalt to roofs. Airborne geometric mean (GM) fume concentrations (benzene solubles) ranged from <0.04 to 2.1 mg/m3 [Brown and Fajen 1977a,b,c]. In another NIOSH industrial hygiene study, fume concentrations were reported as cyclohexane solubles, and a GM concentration of 0.05 mg/m3 was found for roofers applying hot asphalt [Hervin and Emmett 1976]. Puzinauskas [1979] reported similar PBZ fume concentrations for roofers applying Type III roofing asphalt. GM asphalt fume concentrations ranged from 0.8 to 2.1 mg/m3 (benzene solubles) and from 1.2 to 2.9 mg/m3 (total particulates) for all Type III roofing asphalts evaluated.

Industrial hygiene studies conducted by NIOSH in the 1980s found PBZ fume concentrations comparable to those reported in the 1970s. Reed [1983] and Zey et al. [1988] found PBZ fume concentrations (benzene solubles) ranging from a GM of 0.9–1.2 mg/m3 and from not detected (ND) concentrations to 1.4 mg/m3 (no GM determined), respectively, when hot asphalt was being applied to roofs. Similar PBZ sample results were reported by other NIOSH investigators [Tharr 1982; Carson 1986] when either cyclohexane or acetonitrile was used as the extracting solvent for determining asphalt fume concentrations. Tharr [1982] reported GM fume concentrations ranging from 0.17 to 0.28 mg/m3 (cyclohexane solubles), and Carson [1986] found GM concentrations ranging from 0.16 to 0.27 mg/m3 (acetonitrile solubles) for workers operating the kettle and applying hot asphalt to roofs. For roofers laying felt, Brandt et al. [1985] reported similar PBZ exposures ranging from 0.2 to 1.1 mg/m3 (benzene solubles) and 0.5 to 1.7 mg/m3 (total particulates). The GM concentrations for the kettle operator were higher (4.3 mg/m3 benzene solubles and 5.1 mg/m3 total particulates).

In the early 1990s, Schneider and Susi [1993] and Susi and Schneider [1995] reported the results of an industrial hygiene study in which short-duration (11- to 296-min) PBZ samples were collected for the kettle operator and workers applying hot asphalt to roofs. Total particulate concentrations ranged from 10.4 to 28.85 mg/m3, with a single benzene soluble concentration of 21.8 mg/m3 for the kettle operator. Total particulate and benzene soluble concentrations for all other workers handling hot asphalt ranged from <0.03 to 3.66 mg/m3 and 0.08 to 1.89 mg/m3, respectively.

In a cross-sectional exposure assessment study conducted for AI [AI 1991; Hicks 1995], 38 full-shift PBZ samples (sampling periods ranged from 7 to 9 hr) were analyzed from workers involved in the application of hot asphalt to roofs. GM asphalt fume concentrations ranged from 0.36 to 1.0 mg/m3 (total particulates) and 0.19 to 0.67 mg/m3 (benzene solubles). In a recent industrial hygiene study of workers applying asphalt to roofs [Exxon 1997; Gamble et al. 1999], GM asphalt fume concentrations were 0.17 to 0.44 mg/m3 (total particulates) and 0.06 to 0.16 mg/m3 (benzene solubles). The highest concentrations of total particulates (2.73 mg/m3) and benzene solubles (1.23 mg/m3) were found for a roof laborer. Asphalt fume concentrations reported in the more recent exposure assessment studies of roofers [Exxon 1997; Gamble et al. 1999] are somewhat lower than those reported in the 1970s and 1980s. However, no one has conducted comprehensive studies that have related the use of engineering controls, work practices, and worker education to reduced exposures for workers.

Exposures to polycyclic aromatic hydrocarbons (PAHs) have also been evaluated at roofing sites [AI 1991; Hatjian 1995; Hatjian et al. 1997; Hicks 1995]. Hatjian [1995] and Hatjian et al. [1997] reported the results of PBZ samples collected for asphalt roofers using gas chromatography/mass spectrometry (GC/MS). Napththalene, acenaphthene, and phenanthrene accounted for =84% of the measured PAH exposure for roofers. Only one roofer had more than one of three PBZ samples with detectable concentrations of the carcinogenic benzo(a)pyrene (B[a]P); the highest B(a)P concentration reported was 0.2 µg/m3. The kettle temperature at this site was 572 ?F (300 ?C).

Hicks [1995; AI 1991] also collected and analyzed PBZ samples for specific PAHs (see Table 4–7 in NIOSH [2000]). Several types of PAHs were identified in these samples, including the carcinogenic benzo(b)fluoranthene in three PBZ samples. The temperature of the product at the fume source ranged from 325 to 600 ?F (163 to 316 ?C). The method used in the Hicks study was high-performance liquid chromatography (HPLC) with an ultraviolet/fluorescence detector. This method lacks the resolution to reliably identify and quantify discrete PAHs in asphalt fumes (see Section 3.5.3 in NIOSH [2000]).

The Hatjian [1995] and Hatjian et al. [1997] studies as well as the Hicks [1995] study indicate that PAHs may be generated in various asphalt operations under some condition of use. Moreover, asphalt fumes generated at high temperatures are probably more likely to generate carcinogenic PAHs than fumes generated at lower temperatures. At some roofing sites, temperatures have been noted to range from 572 ?F (300 ?C) [Hatjian 1995; Hatjian et al. 1997] to 600 ?F (316 ?C) [Hicks 1995].

4.2.2 Dermal Exposures

To evaluate the extent to which dermal absorption of PAHs may contribute to the total body burden, Wolff et al. [1989] and Hicks [1995] collected skin wipe samples from workers exposed to asphalt during the application of hot asphalt to roofs. The HPLC/fluorescence technique used by these authors cannot reliably identify and quantify components in asphalt, but their results are presented for completeness.

Wolff et al. [1989] collected 10 skin wipes (forehead) and 9 PBZ samples from 10 roofers who had removed an old coal-tar-pitch roof and replaced it with an asphalt roof. PAHs were detected in PBZ samples of these roofers on separate days using HPLC/fluorescence according to NIOSH Method 5506 [NIOSH 1984]. Evaluation of skin wipe samples indicated that total PAH residues per square centimeter of skin were higher in post-shift samples. A significant correlation (r=0.97) was determined between total PAHs found in PBZ samples and in post-shift skin wipe samples of eight of nine roofers. The workers who performed only coal-tar-pitch tear-off all day had higher total PAHs in post-shift skin wipes and PBZ samples than did workers who performed both tear-off and roof replacement. The source of PAHs could not be ascertained during the period when workers applied hot asphalt only, since samples were collected during the entire roof replacement (which also involved the removal of the old coal-tar-pitch roof).

In addition, PBZ samples and skin wipe samples were collected at the end of the work shift from either the foreheads or the backs of the hands of 21 roofers applying asphalt [AI 1991; Hicks 1995]. All skin wipe samples were analyzed for 16 PAH compounds, including anthracene,
B(a)P, chrysene, dibenz(a,h)anthracene, fluoranthene, naphthalene, and phenanthrene (see Table 4–10 in NIOSH [2000]). Only naphthalene (510 to 520 ng/cm2) was detected.