Emissions of hazardous substances from propellants employed in stud guns

Status:

completed 12/2006

Aims:

Stud guns are employed in the construction sector during erection work, for example during fitting or dry construction work. Ignition of a propellant charge causes a fastening element in the form of a bolt to be "shot" into masonry, concrete, or some other material capable of supporting the load. The explosive combustion of the propellant charge causes hazardous substances to be released which are similar in their composition to those used in hand guns and which, when employed in closed rooms, may present a hazard to the equipment operator. The objective of this project was to determine the concentration of various hazardous substances, both in the ambient atmosphere and directly in the air breathed by the equipment operator, in order to permit conclusions concerning the possible hazard to the operator. Several products from a number of manufacturers were considered in the study. In order to ensure that the test conditions were constant and reproducible, the work was performed in a ventilated chamber.

Activities/Methods:

In order to determine the exposure to hazardous substances from the propellants of stud guns, the use of stud guns for driving bolts was simulated under reproducible test conditions in a ventilated chamber at the BG Institute for Occupational Safety and Health (BGIA).
The use of stud guns for the driving of fastening bolts was simulated under laboratory conditions, and the incidence of hazardous substances was measured. The following were measured: respirable dust, inhalable dust, barium compounds, antimony, ammonia, lead and its compounds, nitrogen oxides, carbon monoxide, carbon dioxide and aldehydes.
For the purpose of the study, three stud gun manufacturers known on the German market made their products available (stud guns, propellants and fastening bolts). In order to ensure that the test results were comparable, a uniform test procedure was selected for all products. Each product was tested with 25 bolts in the course of a one-hour test. Differentiation was made between two working positions: upright with the work performed upwards (driving bolts overhead) and upright with the work performed downwards. The concentrations of the hazardous substances were measured both in the test chamber, which was ventilated by a ventilation system (two air changes per hour), and in the air breathed by the equipment operator.

Results:

The stud guns studied exhibited little difference with regard to their hazardous substance emissions; under the defined test conditions, virtually identical concentrations of hazardous substances were measured on all products.

With the exception of those for lead, the concentrations of the measured hazardous substances lay below the corresponding workplace limit values and the relevant limit values based upon the state of the art which were valid up to the end of 2004; in some cases, they also lay below the applicable detection limits for the measurement method employed. Lead and its compounds were measured in concentrations from 0.03 to 0.08 mg/m³. By the use of a supplementary mathematical estimation, it was possible to demonstrate that should the tool with the highest lead emissions be employed for the duration of an eight-hour shift, the EU limit value (0.15 mg/m³) could be attained and the recommended value issued by the insurance institution (0.1 mg/m³) exceeded.

As anticipated, the concentrations of hazardous substances measured in the air breathed by the equipment operator were higher (approximately by a factor of 2) than those measured in the ambient air. The concentrations in the air breathed by the equipment operator were also slightly higher in the overhead working position than in the "normal" working position (upright with work performed downwards).

The results were discussed with the tool manufacturers in the Construction expert committee. Based upon the measurement results for lead, the manufacturers are considering whether the propellant employed to date, which contains lead, can be replaced by a lead-free substitute.

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