Splintery fibres during the use of blasting agents

Status:

completed 10/2013

Aims:

High concentrations of respirable fibres ("WHO fibres") have been detected in some cases by exposure measurements conducted during the blasting of surfaces with a slag abrasive. These fibres were initially classified on the safe side as Category 2 carcinogens according to the provisions of the TRGS 905 technical rules. Very little exists in the way of exposure data and it is not known to what extent different slag blasting agents tend to release fibrous splinters with WHO dimensions during blasting. The purpose of this project, launched by the BG BAU (the German Social Accident Insurance Institution in the Building Trade), was to conduct standardized tests of a larger number of blasting agents in order to compare the fibres released by them. In these tests, samples were also to be obtained which might be used to determine the biopersistence of the respirable fibres released.

Activities/Methods:

A standard blasting chamber was modified at the IFA for conducting of the comparative measurements. A stainless-steel (V2A grade) plate which could be tilted was fitted on one side of the chamber. The blasting gun was fixed in place on the opposite side. The abrasive was positioned outside the chamber in a vessel on a scale, thereby enabling the quantity of abrasive drawn through the hose to be monitored. A sampler (PGP-GSP), screened by means of a baffle plate, was fitted on the enclosure of the blasting chamber for collection of the inhalable dust fraction. The dust collected in this manner was analysed by means of a scanning electron microscope for the concentration of respirable fibres (quantification of the fibres per mg of dust by SEM-EDX following deposition of the dust on a gold-coated capillary pore membrane filter). The greater part of the dust released during the tests was routed out of the blasting chamber through an air outlet and separated off via a pipe on a 150 mm filter. Once the coarse fraction had been filtered off, the dust collected via the air outlet was used for biopersistence tests commissioned by certain abrasive manufacturers independently of this project.

Results:

Splintery fibres classifiable according to their dimensions as WHO fibres were detected in all the slag abrasives studied. The concentrations detected exhibited a wide scatter, however. Concentrations of between around 5,000 fibres/mg and around 500,000 fibres/mg were determined in the dust released during the blasting tests. The dust from certain abrasives collected in the air outlet was studied by external institutes on behalf of the blasting agent manufacturers/distributors for estimation of the biopersistence of the fibrous particles. The results of these tests were considered by the Federal Institute for Occupational Safety and Health (BAuA, Dortmund) to be relevant to the assessment of the carcinogenic potential of the fibres in accordance with TRGS 905. The results showed that all samples studied can be regarded as not being suspected carcinogens. Accordingly, during future use of the abrasives, the requirement will be for observance of the general dust exposure limit (respirable and inhalable dust) to be monitored; the fibre concentration need not be determined.

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