Wood dust from pine beetle killed timber is just one of the factors being investigated in the Babine Forest Products and Lakeland Mill tragedies, however this month, WorkSafe B.C. released a 395 page report solely focussed on safely dealing with workplace wood dust accumulation.
The report zeros in on the best practices to deal with wood dust build up and details housekeeping standards, equipment to combat wood dust and includes examples of current industry practices from several sawmills.
The explosions in Burns Lake and Prince George sawmills prompted a series of follow up actions by industry and government and according to WorkSafe B.C., one key step is to focus on industry practices for wood dust.
WorkSafe B.C. advises minimizing the use of compressed air for clean up as airborne wood dust can explode when coming into contact with any potential ignition sources.
The report also notes that wood dust, will most likely be found in areas that requires sawmill clean up crews to work at heights, including attics, conduit and pipe racks, cable trays and on top of equipment.
Ventilation systems should also be regularly assessed for dust build up.
WorkSafe B.C. say there is five elements necessary to initiate a dust explosion; combustible dust, an ignition source, oxygen, dispersion of dust particles and confinement of the dust cloud.
If one of the five elements is missing, an explosion cannot occur.
Typical ignition sources in sawmills include electrical equipment, static electricity, hot work such as welding or flame cutting, Hilti guns, lighting, metal tools, smoking or open flames and compressors.
According to Interfor [International Forest Products] many of the dust control measures undertaken in sawmills have limitations.
Water misters and sprinklers on log decks are limited to seasonal use due to water freezing issues in winter, roof and wall fans are ineffective in large areas, blow downs are a slow and labour intensive process that doesn't remove dust, but rather moves it to lower levels and also increases atmospheric dust and dust collection systems require a capital investments and are not an absolute fix to the problem.
Weyerhaeuser, one of the largest paper and pulp companies in the world, report their best practices for housekeeping is to limit dust build up to one-eighth of an inch or less and they use cleaning methods like water washing using wet rags and employing contractors that specialize in industrial vacuums that do not generate dust clouds.
A combustible dust explosion scenario included in the report notes that even a small dust explosion has the potential to quickly lead to a larger one. An initial fire starts when an ignition source contacts dust build up, leading to a fire and small explosion. The shock from this explosion will knock dust off elevated surfaces and the newly airborne, fine dry dust ignites, resulting in an expanding fireball. The smaller the dust particles are, the less energy they take to ignite.
If dust clouds are ignited within confined areas, such as buildings or equipment, dangerous pressures can be generated leading to a catastrophic explosion.
According to a report issued by the Occupational Health Administrator in the U.S. in October 2009, there has been approximately 280 dust explosions and fires at industrial sites across North America in the past 20 years. Those accidents caused 130 fatalities and approximately 780 injuries.
The WorkSafe B.C. investigation into the cause of both the Babine Forest Products and Lakeland Mill tragedies is continuing, with evidence from the sites now sent to three expert labs in the U.S. for testing.
As reported in the Lakes District News edition of May 9, 2012, WorkSafe B.C.'s senior vice president Roberta Ellis said that while wood dust was being investigated as a fuel source, other fuel sources such as natural gas and propane are also being investigated.
A natural gas pipe and valve were seized from the Babine Forest Products site for further testing along with two propane tanks and wood dust samples.