Reconstruction of workplace exposure during the welding of rail joints

Status:

completed 02/2007

Aims:

During investigation into a case of suspected occupational disease, the exposure of a welder to polycyclic aromatic hydrocarbons (PAHs) and further pyrolysis products was to be estimated. The insured person was employed as a welder in rail track construction (points and crossing construction) from 1965 to 2000. According to the individual, heavy smoke was observed during welding of the rail joints on the wooden sleepers impregnated with tar oil (creosote or carbolineum). The task was to establish whether or not these fumes were PAHs or other carcinogenic constituents of the wooden sleepers. The problem lay in the fact that measurement data from the period in question were not available, nor were valid data to be found in the occupational disease (BK) report on the subject of BaP years (cumulative BaP dose). The BGM, the institution for statutory accident insurance and prevention in the metals industry in North and South Germany, therefore proposed that the entire working process for the welding of rails be reconstructed.

Activities/Methods:

For reconstruction of the exposure, a company first had to be found which was capable of applying the obsolete welding methods and of obtaining old sleepers impregnated with coal-tar pitch. Stücker Schienenschweissungen, a rail track welding company in Bochum, finally undertook to perform the work. Two series of measurements were performed which were intended to reproduce the working process for the welding of rail joints. Only the welding process employing basic-coated electrodes could be reproduced, however. The first measurement was taken on a construction site of the Deutsche Bahn museum in Koblenz. Care was taken to conduct the measurements during welding processes on old sleepers (approx. 25-30 years old). The second measurement was performed on the site of the BGIA - Institute for Occupational Safety and Health. Since the insured person was employed solely in the area of points and crossings construction, the emissions were to be measured during welding of a joint over a twin sleeper. For this purpose, two short lengths of rail were placed on two approximately 30 year-old sleepers, and welded together. The atmosphere and the sleeper material were analyzed for 16 PAHs.

Results:

The PAH concentrations measured in the wooden railroad sleeper (approx. 500 mg/kg for BaP) are typical for wood impregnated with coal-tar pitch products (creosote or carbolineum). The studies showed that contrary to information in the BK Report on the subject of BaP years 3, exposure to benzo[a]pyrene could not be ruled out during welding work on rails laid on such sleepers. Concentrations of between 0.28 and 1.5 µg/m³ were measured by personal sampling. It should be noted that the high value obtained during the measurement in Koblenz occurred under absolutely worst-case conditions (igniting of the sleepers with the torch). On average, and with consideration of warmer weather conditions, the measurement results overall suggest an exposure of 0.3-0.4 µg/m³. This would place the exposure to benzo[a]pyrene below the former TRK value of 2 µg/m³ in all cases, even under the worst-case conditions described. For calculation of the BaP years in accordance with the BaP Report, application of a maximum concentration of 0.4 µg/m³ is recommended. Consideration must be given during calculation to the fact that the welding work did not exceed five hours per shift (exposure share 5/8). The reproduced exposure measurements enabled the available data for the area of rail track welding to be extended, and calculation of the BaP years to be simplified.

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