Paper360 - May/June 2013 - (Page 27)

DUST FIRES TECKLINK Managing the Risk of Fire and Explosion in the Pulp and Paper Industry Between 1980 and 2005 there were 281 explosion incidents, 66 of which were attributed to wood and paper dust STEVEN J. LUZIK R eported combustible dust fires and explosions in the pulp and paper industry have been relatively scarce compared to other types of combustible dusts such as food, wood, metals and rubber. In the 25-year period from 1980 to 2005, there have been a total of 281 explosion incidents, 66 of which were attributed to wood and paper dust (Figure 1). These explosions resulted in 11 fatalities and 88 injuries and occurred in dust collectors, particle size reduction equipment, silos, storage bins and inside plant buildings where housekeeping issues existed. Of the 66 incidents, two were associated with paper dust. Pulp dust was never mentioned in the database details which may be due to the fact that pulp and paper particulate tends to be non-spherical and fibrous in nature, particularly particles larger than 150 microns in size. Particles generated as a result of pulp and paper making operations do not lend themselves to formation of finely divided uniform dust clouds when suspended in air (Figure 2). The agglomerations, when disturbed by air movement including blow-down with compressed air, tend to result in suspensions that are isolated in nature, of small volume and not dense enough to create a cloud that will propagate flame in the presence of a credible ignition source. The relatively low bulk density of pulp and paper dusts (typically less than 160 kg/m3 or 10 lb/ft3) also offers a benefit in terms of explosion risk. A relatively thick accumulation of paper or pulp dust must be present to create a secondary dust explosion risk in a room or building when compared to other combustible dusts such as Figure 1. CSB incident data, 1980-2005. coal, agricultural and food dust, metal dust and even wood.1 Paper and pulp dust is also extremely hygroscopic and wetting of the particles above 5 percent can offer a benefit in terms of decreasing the sensitivity of the dust cloud to ignition and lowering the severity of the resulting explosion. Despite the low incidence of dust explosions in the industry operators should not become complacent. Sound administrative and engineering controls must be put into place and followed if the plant is to be managed effectively. The risk of a combustible dust fire in these plants is also significant. The relatively low bulk density of the dust and agglomerations that are produced, in conjunction with dust generation, actually increase the risk of fire due to increased surface area and porosity that allows air to easily mix with the dust. Some pulp and paper producing plants have a green wood section where trees are received, debarked and chipped in preparation for digestion. These areas may generate dry wood dust that easily forms combustible clouds, when suspended, and can lead to fire and explosions if proper controls are not in place. The incident history reveals that many fires and explosions have occurred where wood dust is handled. CONDITIONS REQUIRED FOR DUST EXPLOSIONS TO OCCUR Th ree elements are required for a fi re including: a fuel; an oxidant, typically the oxygen in air; and a sufficiently energetic ignition source. Together these elements are commonly referred to as the “fi re triangle.” If any one of these three elements can be removed, fi re cannot be initiated. The fi rst two of these elements—the fuel and oxidant—when in an appropriate ratio, are referred to as the flammable atmosphere. For an explosion involving a combustible dust to occur, two additional requirements are necessary: suspension or mixing of the combustible dust in air, in small enough particle sizes, above the lower explosive limit; and confinement. These two additional requirements combine with the fire triangle to form the “Explosion Pentagon” (Figure 3). Generally speaking dust particles must be of small diameter, usually below 0.45 - 0.5 mm (450 to 500 microns). However, in the real world, dust particles are not often spherical in nature and can be needle shaped or flake like. The 2012 edition of the NFPA 664 standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Paper360º MAY/JUNE 2013 27

Table of Contents for the Digital Edition of Paper360 - May/June 2013

Over the Wire . . . News Summary
The 2013 TAPPI Award Winners
Successful Asset Management in the Paper Industry from an OEM Point of View
TAPPI Journal Summaries
Managing the Risk of Fire and Explosion in the Pulp and Paper Industry
Broadening the Availability of Carbon Fibers with Lignin
TAPPISAFE Through the Eyes of a Labor Attorney
Bleached Softwood Kraft Pulp
Association News
What’s New on

Paper360 - May/June 2013