Canadian Occupational Safety

28 Canadian Occupational Safety www.cos-mag.com dusts and powders are aluminum, magnesium, tantalum, titanium and zirconium. While metal dust is a known hazard, Norval says, people generally underestimate the likelihood of explo- sions caused by metal processing. "When people think about metals in their day-to-day life, they think they aren't reactive (the quality of reacting spontaneously, rapidly and with heat). But aluminum or iron dusts are actu- ally quite reactive. If you shred that dust fi nely and get it dispersed in the air and with a large enough amount of heat, it can take off," he says. The hazard severity of plastic dusts varies according to the type of plastic and additives. Fibreglass, for example, tends to smoulder rather than fl are up and burn, Norval says. Moreover, companies often use processes that avoid dust creation. "Most places, when they recycle the polymers don't get into the same processes. They can melt it down and process it as a hot liquid rather than having to shred it," he says. However, many dust explosions involve plastic materials. For example, the processing of polyethylene, the plas- tic used to make grocery bags, presents dust explosion hazards, Amyotte says. "So polymers like that, plastics, resins, they're quite hazardous. If you're shredding plastics, if you're reducing the particles and generat- ing particles of material down in the explosive range, maybe 100 or 200 microns (1,000 microns = one millimetre), you have to be careful." The presence of combustible plas- tic in many appliances has made their recycling more hazardous. According to a 2005 study on dust explosions in industrial wastes, the recycling of refrigerators is particularly dangerous, in part due to the use of combustible insulation materials, such as poly- urethane. This use, the researchers say "produces explosive dust clouds during the crushing operation and transportation of shredded materials." Moreover, the foaming agent used for the polyurethane is cyclopentane, a fl ammable gas. Together, the sub- stances create an explosive atmosphere around dust particles, so any impact, friction or collision caused by crushing or compacting machines will ignite the dust cloud. "These fi ndings show that the dusts produced in the recycling process can lead to dust explosion easily," the study concludes. Because of the number of different kinds of dust that may be present in a facility, companies should have their dusts analyzed, says Simon Fridly- and, president of S.A.F.E. Engineering in Toronto. "In the recycling industry, you may be handling all sorts of types of prod- ucts, so you may have different types of dust. One dust is different from another as far as the explosive charac- teristics are concerned, so it is diffi cult to establish the different characteristics of the dust unless you test," he says. • automatic dust explosion suppression systems • mechanical isolation valves. TRAINING FUNDAMENTALS Managers and workers need to be trained in the fundamentals of a dust explosion, Amyotte says. By under- standing the explosion pentagon — fuel, oxidant, ignition source, con- fi nement and mixing or suspension — they can identify the conditions they need to try to eliminate. Thus, everyone understands proper housekeeping will eliminate the fuel. They will also be looking for ways to reduce ignition sources and prevent actions that cause dust to be raised and suspended in an open area. Of course, managers should also ensure workers understand the hazardous properties of the specifi c dusts being handled, usually through the use of safety data sheets. "I go back to education," Amyotte says. "If vents are being used in your facility, operators should know why they're there and what problem they're dealing with. Managers should know what the frequency of inspection needs to be and make sure those inspections are done. All these different levels of responsibility mean you need different knowledge. But, everyone should have the fundamental training in process- ing a combustible dust." The A.L. Solutions explosion in 2010 caused the shutdown of the plant. Fol- lowing its investigation, the United States Chemical Safety Board recom- mended the company comply with NFPA 484, develop training materials addressing combustible dust hazards, train employees and conduct regular refresher training. Norval says fi res and explosions in recycling facilities happen more often than people think. He advises managers to never rely on any particular control measure, such as dust analysis, or on workers always following procedures. "If we plan for the worst and make sure the worst can never happen, then we're making sure things don't happen," he says. "That's prevention." Linda Johnson is a freelance writer based in Toronto. She can be reached at lindajohnson@sympatico.ca. Testing determines the major param- eters such as Kst value (maximum rate of pressure rise); MIE (minimum ignition energy); and Pmax (maxi- mum pressure in constant-volume explosion). Dust explosions are prevented — and their impact limited — primarily through a good housekeeping program. Employees must be cleaning regularly, Fridlyand says, especially to remove dust accumulated on elevated surfaces and hard-to-see building structures. "Where you have ledges or a joist in the air, that's where the dust buildup takes place and where there may be a thick layer of dust," he says. "If you have even a minor explosion, it could cause a second and even a third. It's like a cascade. And that could be devas- tating, destroying entire buildings and complexes. It is very important to make sure there is no dust accumulation." Another basic prevention strategy is a dust collection system, which extracts dust in the area where it is generated, he adds, such as at shred- ding machines. The system must be designed to mitigate a potential dust explosion inside the system itself (through venting, for example). Collection systems and other pre- vention and protection equipment must be designed and positioned by professional engineers. In Ontario, Fridlyand says, under the PSR (pre-start health and safety review) program, all new and modifi ed equipment needs to be registered to ensure its compliance with current and applicable standards. In recycling facilities, too, it's important to separate hazardous materials and processes. As the NFPA 484: Standard for Combustible Metals advises, combustible metals should be separated from other combustible material, such as wood pallets and cor- rugated cardboard, that could provide extra fuel in case of a fi re. Other protection methods include: • grounding and bonding (to remove electrostatic ignition sources) • hot-work permitting • explosion relief (such as explosion relief walls to prevent building collapse) • explosion relief venting SAFE RECYCLING Sorting recycling can be hazardous to workers' health and safety, according to a recent report. Seventeen recycling workers died on the job between 2011-13 in the United States, and they are more than twice as likely to be injured at work. These high injury and fatality rates are a result of unsafe working conditions, including: • loud noise and vibration • extreme temperatures • long hours and fatigue • respiratory hazards (dust and other airborne contaminants) • awkward postures, such as leaning over conveyor belts sorting materials • heavy equipment in dangerous situations (climbing onto and into massive conveyor belts and balers to clean them) • risk of being struck by huge front-end loaders, forklifts and falling bales • handling dangerous materials that should not be on the recycling line, such as used needles, chemicals, dead animals and broken glass. Source: Sustainable and Safe Recycling: Protecting Workers Who Protect the Planet States, and they are more than twice as likely to be injured at work. • respiratory hazards (dust and other airborne contaminants) Safety Is No Accident. Ensure your protection with FireZero innovative technology and superior comfort garments. www.tosaveandtoprotect.com

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