Document a1Bm3o841rMwzmB70x33ggZKe

Alternative fomu of control for dust generated during the cleaning of brake assemblies 39 DISCUSSION The results for the vacuum funnel vs. blow-off experiment and for the vacuum brush versus blow-off are shown in Table 1. It can be seen that the background concentrations during the fifth hour had re-established at the original level after a 2 hr latent period and therefore the blow-off operation carried out during the second hour did not affect the concentrations observed in the vacuum ftinnd samples collected in the sixth hour. The ftinnefappears to reduce personal exposure by 2 per cent for particles and 40 per cent for fibres; concentrations observed in the adjacent bay are increased and a reduction in peak concentrations ofabout 90:1 was achieved. During the second experiment there was more variability in the background con centrations between tbe first and fi/Ut hour* but the effect of blow-off on the vacuum brush test may be discounted. Personal exposure by use of the brush is reduced by 75 per cent for both particles and fibres and the static samples show a reduction of 20 per cent for particles but an increase of 12 per cent for fibres. A reduction of 80:1 in peak concentrations was again observed. CONCLUSION Tbe experiments demonstrated that the vacuum brush was better in reducing operator's exposure; it had the added advantages over the funnel of being easiet to handle, consisted of fewer, simpler parts and was much quicker than the vacuum funnel. There are three major reasons for the relative inefficiency of the funnel; its use increased brake cleaning time (and thus exposure time) by a factor of 8, it was difficult to obtain a good seal at the skirt, and imbalance occurred between the necessary air input and the capacity of the available exhaust system, with resulting leakage of dust REFERENCE Cooomi on Hygiene Standards, British Occuvationai. Hygiene Society (1941) Hytlm Standards for CkrysotUs Asbtstos Dust. Pergvnon Pico, Oxford.