Wednesday, September 4, 2013

Wood dust can explode in dry or wet state: Report

B.C. sawmill study makes surprise finding on using moisture to prevent deadly explosions

Wet wood dust is just as explosive as
dry wood dust, a report shows. 
The smallest-sized wet wood dust is just as explosive as dry wood dust from B.C. Interior sawmills, according to a report prepared by FPInnovations for the provincial sawmill sector.

The finding raises questions about the usefulness of misting at sawmills. It was part of a first-of-its-kind study in British Columbia ordered after a pair of deadly sawmill explosions in the province last year that killed four workers.

“It was assumed moisture would be a bigger factor,” said Darrell Wong, one of the report’s authors. He is a manager of FPInnovations, the non-profit forestry research centre at the University of B.C.

But Wong said more study must be done before sawmills should consider jettisoning misting systems. Misting systems have a secondary function of knocking wood dust out of the air.

Wood dust suspended in the air was confirmed as the fuel source for the two explosions by WorksafeBC, the province’s chief workplace safety agency.

As part of the new study, hundreds of dust samples from 18 sawmills were analyzed, with some samples sent to Chilworth Technologies, a lab in Princeton, N.J. that determines how explosive substances are.

The report has been made widely available through forest industry associations and the United Steelworkers, which helped fund the study. WorkSafeBC is also helping to distribute the report.

The study also found there is not much difference among the explosiveness of various types of wood dust of timber, including type of wood (spruce, pine, fir, Douglas fir or cedar) and timber killed by the mountain pine beetle. That suggests timber killed by the beetle has not had its properties changed to make it more explosive, said the report.

But the report said the milling of beetle-killed pine may create more dust or dust that is easier to raise into a cloud than other woods. Among the factors needed to create a dust explosion is fine particles suspended in the air.

FPInnovations applied two criteria to determine which areas in the sawmills were at greater risk of an explosive hazard: the accumulation of wood dust at a rate of greater than one eighth of an inch in an eight-hour shift and samples that have more than 40 per cent of particles that were 425 micrometres (just under half a millimetre) or less in size.

Just 20 wood dust samples met those criteria, with 14 of those from mills that were processing beetle-killed timber. A majority of these samples were collected from under or near conveyors and in basements.

A sawmill explosion at Babine Forest Products near Burns Lake on Jan. 20, 2012 killed two workers. An explosion at Lakeland Mills in Prince George on April 23, 2013, killed another two workers. Dozens more workers were injured in the two explosions and fires.

This article was edited for length. Source: The Vancouver Sun

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