Dust emissions of wall chasers

Status:

completed 07/2003

Aims:

In the past, the production of chases in walls for cables or pipes entailed considerable work. In order to facilitate this work, manually guided electric tools (wall chasers) were developed. These tools enable the work to be completed relatively quickly, but have the disadvantage of creating higher dust emissions. Owing to the material composition of the walls to be chased, the dust produced often contains quartz. Workplace measurements indicate that the dust impact may exceed the threshold values.

Activities/Methods:

The following points were studied on a test bench in accordance with EN 1093-8, "Safety of machinery - Evaluation of the emission of airborne hazardous substances - Part 8: Pollutant concentration parameter, test bench method": dust emission with and without suction, capture efficiency, filtration performance, state of the art. The test conditions followed the specifications of DIN EN 50144 Part 1, "Safety of hand-held motor operated electric tools, General requirements". The emissions of respirable dust not captured were measured. The particle size distribution was also measured, and preliminary tests performed for measurement of the quartz component.

Results:

Two basic types of wall chasers are available: those with two cutting discs (representing the majority of tools tested and available on the market) and those with cutter head. The first of these types leaves a web, which must be broken out, for example with a chisel. The latter leaves no web, and the volume of machined material is correspondingly higher. The particles produced in this case are however larger, with the result that the proportion of respirable dust is lower than that produced by wall chasers with cutting discs. The quartz component of the test material was shown to be reflected in the respirable dust component of the samples studied. The dust emissions produced by some of the tools were considerable. The emissions were so high that the (workplace) limit values for quartz and respirable dust, which had been employed for the sake of comparison, were substantially exceeded on the test bench by some of the tools. At the same time, the capture rate exceeded 90% of the machined material. Substantial development work remains to be done in order to raise the capture effiency. The plunge phase of the chase cutter into the material was shown to have a considerable influence upon the dust emission. It is important that attention be paid to this aspect; important information can be found in the instruction handbook. Further developments should address optimization of the capture of dust emissions, not least during the plunge phase, and the optimum combination of wall chaser cutter and mobile dust remover.

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