SAMPLING AND ANALYSIS OF BITUMEN FUMES

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Abstract
Processes which involve the use of bitumen-containing materials at elevated temperatures can release airborne particulates into the workplace. The organic part of the particulates, characterized by the benzene-soluble matter (BSM), mainly stems from the bitumen and contains small amounts of polycyclic aromatic hydrocarbons (PAHs). A sampling and analytical procedure for the determination of total particulate matter (TPM) and BSM for bitumen fume in the atmosphere has been developed and validated. Its suitability for sampling PAHs has been investigated. The sampling package consists of a glass-fibre-silver membrane combination supported by a back-up pad, all contained in a standard 37 mm Gelman-type filter cassette. The glass-fibre-silver membrane filter combination was shown to have a maximum capacity of 6 mg. Some loss of BSM was shown to occur owing to evaporation during sampling, but for a 5 mg sample losses are not expected to be greater than 2% mass per hour of sampling under normal operating conditions. The sampling procedure has also been shown to be suitable for PAHs, although evaporative losses may lead to a relative deficiency of the lower molecular weight PAHs in samples containing small amounts of material. By this method personal breathing-zone samples of the mixed aerosol have been taken for analysis, giving TPM, BSM and information on the content of certain three- to seven-ring PAHs. Airborne concentrations have been measured for 17 jobs in six processes in manufacturing, road application, roofing, and indoor mastic laying. The materials contained bitumen, stone and cutback solvent, giving rise to potential exposure by inhalation and skin contact. Time-weighted average exposures over 8 h (TWA (8 h)) ranged from 0.2 to 18 mg m −3 for TPM, 0.1 to 14 mg m −3 for BSM and 4 to 2508 ng m −3 for a total of eleven selected PAHs. The BSM varied from 0.5 to 84% of the TPM depending on the materials being used. Exposures are compared showing the effects of material, temperature, job and indoor working: the findings are in general agreement with other published work. Generally, the exposure to PAHs is related to the amount of BSM. For laboratory studies of the emission of fumes from hot bitumens and the analysis of three- to seven-ring PAHs in those fumes, a laboratory rig has been developed and validated, in which we can reproducibly generate and sample bitumen fumes under controlled conditions. The results obtained with the laboratory rig are shown to be related to those obtained in the field from the same product. Condensed bitumen fumes are characterized briefly in terms of their chemical composition, boiling-point distribution and viscosity. Total fume emissions, measured as BSM and the concentrations of a number of individual PAHs in the BSM have been determined for penetration (paving) grade bitumens and for oxidized (roofing) grade bitumens at temperatures relevant for the practical applications. A comparison is made between bitumens and coal-tar pitches and the fumes generated from them. The PAH contents of fumes from penetration grade bitumens and oxidized grade bitumens were similar. The major factor controlling variations in PAH emissions from hot bitumens was the amount of fume generated, measured as BSM, and this is shown to be markedly dependent on the bitumen temperature. The coal-tar fumes contained far more PAHs than the bitumen fumes. BSM exposure provides a good indication of relative exposure to PAHs in bitumen fume particulates released from normal bitumens under typical application conditions.