Pii: S0003-4878(99)00038-1

Materials used in the construction industry frequently contain large quantities of silica. When they are cut or shaped with power tools considerable respirable dust can be produced. Three dust control systems for use with cut-o€ saws have been evaluated on site: wet dust suppression using mains water, the same system using water from a portable water tank, and local exhaust ventilation. The eciency of water suppression on cut-o€ saws has been precisely quanti®ed in controlled laboratory conditions by means of measurements with and without dust control. When dust control was used on-site, the mean concentrations of airborne silica were reduced by a factor of between three and seven, the accuracy being limited by the relatively high limit of detection for silica. All controls systems generally reduced respirable dust levels by at least 90%. Although the e€ectiveness of dust suppression did not depend on blade type, a diamond blade was more e€ective than a resin-bonded blade with the pressurised water system; cutting a slab with this type of blade could be completed before the water tank required repressurisation. In laboratory tests, the application of water reduced the dust concentration to <4% of its value without control. The method for monitoring the dust concentration was suciently sensitive to measure a di€erence in concentration produced during cutting in di€erent directions. It is important, however, that the pressure in supply reservoirs is properly maintained, that the water is correctly applied and that it is used at the correct rate. If this is done e€ective dust control can be achieved. Crown Copyright # 1999 Published by Elsevier Science Ltd. All rights reserved.