ASPHALT FUME EXPOSURES DURING THE
MANUFACTURE OF ASPHALT ROOFING PRODUCTS
Current Practices for Reducing Exposures
 
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4. Occupational Exposure to Asphalt Fumes
 
  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 the 1977 criteria document, NIOSH established a recommended exposure limit (REL) of 5 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 testimony to the Department of Labor, NIOSH recommended that asphalt fumes be considered a potential occupational carcinogen [NIOSH 1988]. In 2000, NIOSH conducted a review of the health effects data available since publication of the 1977 criteria document. 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 fumes is 0.5 mg/m3 (benzene-soluble aerosol) as an 8-hr TWA concentration with an A4 designation, indicating that it is not classifiable as a human carcinogen [ACGIH 2001].
 
  4.2 Potential for Exposure
 

Dermal contact with hot asphalt can cause burns, and asphalt fumes or vapors can be absorbed through the skin. Information is limited on the occurrence of exposure to asphalt fumes during the manufacture of asphalt roofing products. Five NIOSH health hazard evaluations (HHEs) conducted during the 1970s listed personal breathing zone (PBZ) concentrations ranging from 0.3 to 32 mg/m3 for total particulates and 0.21 to 6.8 mg/m3 for the cyclohexane solubles [Apol and Okawa 1977, 1978; Okawa and Apol 1977, 1978a,b] (see Table 4–1). In a cross-sectional exposure assessment study conducted for the AI [AI 1991; Hicks 1995], data indicate that PBZ measurements ranged from 0.068 to 13 mg/m3 for total particulates; PBZ measurements ranged from 0.013 to 3.7 mg/m3 for benzene solubles [AI 1991; Hicks 1995] (see Table 4–1).

An analysis of the 34 full-shift PBZ samples (most sampling ranged from 7 to 9 hr) indicates that the geometric mean (GM) for total particulates was 1.4 mg/m3 and the GM for benzene solubles was 0.27 mg/m3 [Hicks 1995] (see Table 4–2). In another study [Exxon 1997], analysis of 77 PBZ samples indicates that the GM for total particulates was 0.6 mg/ m3 and the GM for the benzene soluble fraction of the samples was 0.08 mg /m3.

In the Hicks [1995] study, PBZ and dermal wipe samples were also collected and analyzed for specific PAHs (see Tables 4–7 and 4–9 in NIOSH [2000]). Several types of polycyclic aromatic hydrocarbons (PAHs) were detected in these samples (see Table 4–7 in NIOSH [2000]). The method used in the Hicks study was high performance liquid chromatography (HPLC) with an ultraviolet/fluorescence detector (NIOSH Method 5506) [NIOSH 1994, 1998]. This method lacks the resolution to reliably identify and quantify discrete PAHs in asphalt fumes (see NIOSH [2000], Section 3.5.3).

The asphalt roofing products manufacturing industry summarized exposure data collected during 1980–1997 at 53 plants of 4 companies (A, B, C, and D). The data were from 1,920 samples for total particulates and 1,184 samples for benzene or cyclohexane solubles as TWAs [Fayerweather 1998]. Exposure data were not provided by job title because job titles were inconsistent among companies and did not always relate to a location or task on the manufacturing line. An attempt to classify the jobs into three exposure groups was unsuccessful because sampling was reported to have been conducted during nonroutine tasks and conditions. Figures 4–1 and 4–2 compare the average exposure data for total particulates and benzene/cyclohexane solubles for 1980–1989 and 1990–1997 from the four companies. (No comparison data were available for company D, since data were collected only for 1995–1997.) These figures indicate that average exposures, expressed either as total particulates or as benzene/cyclohexane solubles, declined after 1990 for companies A, B, and C.

No conclusions can be drawn as to the statistical significance of this observation, however, since statistical analyses were not conducted and raw data are not available for additional analyses.

The asphalt roofing manufacturing industry attributes this apparent reduction in average exposures after 1990 to the following: (1) the elimination of the saturator process by converting from paper roofing felts to glass fiber mats, (2) the improvement of capture efficiency of exhaust hoods, (3) the conversion to closed saturators on several operations, and (4) the reduction of fugitive emissions subject to the U.S. Environmental Protection Agency (EPA) regulations under the new source performance standards (NSPS) and other 1990 Clean Air Act Amendment requirements. By 1990, most plants had eliminated the saturator process and implemented other controls (not specified).
 

Table 4–1. Asphalt fume exposures for various occupations during manufacturing of roofing products
 
Breathing-zone samples
Exposure concentration (mg/m3)
Reference, source of exposure, and occupation
Type*
Number
Range
Geometric mean
Arithmetic mean
Apol and Okawa [1977],
production of asphalt shingles and rolled roofing materials:
Saturator operator
Total particulates
Cyclohexane solubles
3
2
 2.2–7.3
0.81–2.6
4.9
1.4
5.6
1.7
Coater operator
 Total particulates
Cyclohexane solubles
2
2
 14–15
0.87–6.8
14
    2.4
14
   3.9
Coater trainee
 Total particulates
Cyclohexane solubles
2
2
11–15
0.30–2.3
13
      0.84
13
   1.3
Press operator
Total particulates
Cyclohexane solubles
2
2
6.1–32
1.4–1.5
14
    1.4
19
     1.42
Seal-down operator
Total particulates
Cyclohexane solubles
2
2
0.99–1.4
0.43–1.2
1.2
  0.71
1.21
0.81
Foreman
Total particulates
Cyclohexane solubles
2
2
5.3–6.3
0.47–0.53
5.8
  0.50
5.8
0.5
Laminator operator
Total particulates
Cyclohexane solubles
7
5
0.96–2.16
0.23–0.76
1.6
  0.46
1.6
  0.50
Okawa and Apol [1977],
production of asphalt shingles:
Laminator operator
Total particulates
Cyclohexane solubles
8
8
0.38–5.2
0.24–3.1
1.0
  0.76
1.4
  1.05
Saturator/coater
Total particulates
Cyclohexane solubles
6
6
5.3–29
0.66–1.3
8.03
0.88
12
     0.91
Apol and Okawa [1978],
production of asphalt shingles and rolled roofing materials:
Saturator operator
Total particulates
Cyclohexane solubles
1
1
†
 †
2.4
  0.76
2.4
  0.76
Coater
Total particulates
Cyclohexane solubles
2
2
12–16
0.21–1.1
14
      0.47
14
     0.64
Wrapping machine operator
Total particulates
Cyclohexane solubles
1
1
†
†
1.4
  0.77
1.40
0.77
Lead man
Total particulates
Cyclohexane solubles
1
1
†
†
5.3
  0.76
5.29
0.76
Presser
Total particulates
Cyclohexane solubles
2
2
8.3–22
0.30–0.54
13
       0.402
15
     0.42
Okawa and Apol [1978a],
production of asphalt shingles and rolled roofing materials:
Coater
Total particulates
Cyclohexane solubles
2
2
4.2–5.1
3.3–3.9
4.6
3.6
4.7
3.6
Cooling section operator
Total particulates
Cyclohexane solubles
2
2
0.3–1.0
0.7–1.6
0.55
1.06
  0.65
1.2
Machine tender
Total particulates
Cyclohexane solubles
2
2
0.4–2.8
0.6–1.8
1.06
1.04
1.6
1.2
Okawa and Apol [1978b],
production of asphalt shingles and rolled roofing materials:
Saturator operator
Total particulates
Cyclohexane solubles
1
1
†
†
1.0
2.1
1.0
2.1
Coaterman
Total particulates
Cyclohexane solubles
1
1
†
†
2.1
  0.22
2.1
  0.22
Slateman
Total particulates
Cyclohexane solubles
1
1
†
†
3.4
  0.21
3.4
  0.21
Pozzoli et al. [1985],
asphalted paper production:
Paper production workers
(smokers)
Total PAHs
4
0.0048–0.036
0.009
0.014
Paper production workers
(nonsmokers)
Total PAHs
2
0.0034–0.311
0.010
0.017
AI [1991]; Hicks [1995],
Roofing manufacturing
(temperature of product at fume source from 300 to 468 °F [149 to 244 °C]):
Loader/asphalt handler
Total particulates
Benzene solubles
6
6
0.068–0.94
0.041–0.71
0.51
0.31
0.66
0.41
Slate blend operator
Total particulates
Benzene solubles
4
4
1.1–13
0.013–0.94
3.9
   0.077
5.6
  0.27
Coater operator
Total particulates
Benzene solubles
8
8
0.42–2.5
0.049–1.6
1.0
0.2
1.3
  0.37
Machine operator
Total particulates
Benzene solubles
8
8
0.8–4.4
<0.071–3.6
1.6
0.55
1.9
1.5
Press operator/cooling
operator
Total particulates
Benzene solubles
7
7
0.55–11
<0.085–3.7
2.6
  0.32
4.8
1.0
Supervisor
Total particulates
Benzene solubles
1
1
†
†
1.4
  0.32
1.4
  0.32

*The sampling and analytical methods used for measuring benzene solubles and polynuclear aromatic hydrocarbon (PAH) concentrations may vary between studies and these results may not be directly comparable.

†Information not provided.

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Table 4–2. Exposures during manufacture of asphalt roofing products
Concentration (mg/m3)
Sample type
Range
Geometric mean (GSD)*
Arithmetic mean (SD)
Median
Total particulates
0.068–13
1.4 (3)
2.6 (3.1)
1
Benzene-soluble fraction
<0.071–3.7
    0.27 (4.4)
 0.76 (1.1)
    0.24

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Figure 4-1 . Total particulates pre- and post-1990, by company. (Source: Fayerweather [1998].)

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Figure 4-2. Benzene/cyclohexane solubles pre- and post- 1990, by company (Source: Fayerweather [1998].)

 

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  4.3 Operations and Jobs with Potential for Asphalt Fume Exposure
 

The basic manufacturing process for all asphalt roofing products is essentially the same, with slight modifications, depending on which product is being produced. Figure 3–1 presents the diagram of a typical asphalt roofing manufacturing line.

The operations that pose a potential for worker exposure to asphalt fumes involve hot liquid asphalt. These operations include the following:

  • The delivery, in-plant transfer, and storage of asphalt flux and the various roofing asphalts used in the manufacturing process
  • Unloading techniques—coupling flexible pipe to a tanker and pumping hot asphalt into appropriate storage tanks
  • Pumping hot asphalt into a large open funnel connected to a surge tank, then pumping hot asphalt into storage tanks
  • Incorporating mineral stabilizers to coat asphalts and, in the case of modified asphalt products, to blend polymers in mixing tanks
  • Using the coater (or the impregnation vat in the case of modified bitumen products) where liquid coating asphalt is applied to the surfaces of the felts
  • Using the saturator (which is used before or in lieu of coating in the case of organic felts) where the felts are sprayed with and then immersed in a saturant asphalt
  • Conducting quality control activities associated with testing raw materials
  • Conducting production activities with line breaks requiring maintenance
  • Conducting off-line laminator operations where hot asphalt is heated and applied between two or three layers of shingles
 
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