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In February 1999, a fire at a Massachusetts foundry extended into the ventilation ducts. A small, primary explosion within the ductwork dislodged some of the heavy deposits of phenol formaldehyde resin dust that had settled on the outside of the ducts. This produced a dust cloud that fuelled a secondary explosion powerful enough to lift the roof and cause wall failures. Three people were killed, and nine were injured.
Another seven people were killed and 37 injured in February 2003, in a dust explosion at a Kentucky acoustics insulation manufacturing plant. The report from the U.S. Chemical Safety and Hazard Investigation Board (CSB) said the blast was likely caused by a small fire extending from an unattended oven, which ignited a dust cloud created by a nearby line cleaning. A deadly cascade of dust explosions followed throughout the plant.
Because of these incidents, the CSB conducted a major study of industrial accidents involving dust explosions over the past 20 years. The CSB found that during this period in the United States alone, there have been more than 150 serious industrial dust explosions, resulting in 80 deaths. And the issue extends beyond the U.S. Statistics show that fire/explosion hazards exist in any facility or equipment that handles or processes a combustible dust.
A combustible dust explosion hazard may exist in a variety of industries, including: food (e.g., candy, starch, flour, feed), plastics, wood, rubber, furniture, textiles, pesticides, pharmaceuticals, dyes, coal, metals, and fossil fuel power generation. Most natural and synthetic organic materials, as well as some metals, can form combustible dust. The safety bulletin prepared by the U.S. Occupational Safety and Health Administration contains important information on how to assess the risk in your facility.
Elements of a Dust Explosion
Experts agree that for a dust explosion to occur, five conditions must be present at the same time. First, the three elements needed to cause fire (fire triangle):
1. combustible dust (fuel)
2. ignition source (spark or heat)
3. oxygen in air (oxidizer)
plus additional elements needed for a combustible dust explosion:
4. dispersion of dust (into the air forming a dust cloud)
5. confinement of the dust cloud (building or ceiling)
These five elements make up the "explosion pentagon" that causes a dust explosion. If one of the elements of the explosion pentagon is missing, a catastrophic explosion cannot occur.
A dust cloud that is ignited within a confined or semi-confined vessel, area, or building, burns very rapidly and may explode. This could cause fires, additional explosions, flying debris, and the collapse of parts or all of the building.
An initial explosion that occurs in processing equipment or in an area where there is an additional accumulation of dust, may shake the renegade dust loose, or damage a containment system (such as a duct or vessel). The additional dust released into the air, if ignited, can cause one or more secondary explosions that can be even more destructive than the first.
Reducing the risk
Facilities should conduct a dust hazard assessment to carefully identify materials that can be combustible, processes that use, consume, or produce combustible dusts, open areas where combustible dusts may build up, hidden areas where combustible dusts may accumulate, ways that dust may be dispersed in the air, and potential ignition sources.
The key factor is whether or not the specific dust from your facility is a combustible dust hazard. Although there is currently no combustible dust hazard class under WHMIS, there is a requirement to declare all hazards of the product on the Material Safety Data Sheet (MSDS). Unfortunately, the dust explosion hazard is under-recognized and often not declared on MSDSs. In CCOHS' CHEMINFO database, the potential for a material becoming a combustible dust hazard has been identified. As well, any reports of dust explosions involving the chemical are included. Laboratory testing of your specific dust will help tell you if there is a hazard at your workplace.
The facility analysis must also identify areas requiring special electrical equipment classification due to the potential combustible dust hazard.
The following safety practices are recommended:
Dust control - the most important step towards prevention of dust explosions
- Minimize the escape of dust from process equipment or ventilation systems. Use dust collection systems and filters, and try to use surfaces that minimize dust accumulation and are easy to clean.
- Prevent the accumulation of dusts on surfaces. Use surfaces that minimize dust accumulation and are easy to clean.
- Inspect for dust residues in open and hidden areas, and clean them at regular intervals.
- Use cleaning methods that do not generate dust clouds (ie. vacuum rather than blow or dry sweep).
Only use vacuum cleaners approved for dust collection. Locate relief valves away from dust hazard areas.
- Develop and implement a program for hazardous dust inspection, testing, housekeeping, and control program that establishes, in writing, the method and frequency of these steps.
- Use appropriate electrical equipment and wiring methods.
- Keep static electricity under control; this includes bonding of equipment to ground.
- Prevent smoking, open flames, and sparks, mechanical sparks and friction. Use separator devices to remove foreign materials capable of igniting combustibles from process materials.
- Avoid contact between heated surfaces and dusts. Separate heating systems from dusts.
- Ensure the proper use and type of industrial trucks, and the proper use of cartridge-activated tools.
Facility owners, managers and supervisors are responsible for conducting a facility analysis (ideally before introducing a hazard) and for developing a prevention and protection plan that addresses the specific needs of their operation. Their responsibilities also include improving policies and procedures, and taking whatever action is necessary to prevent a dust explosion. Employees, are responsible for adhering to safe work practices, and as the people closest to the source of the hazard, should be trained and encouraged to take an active role in recognizing unsafe conditions, taking preventative action, and alerting management. All employees should be trained in safe work practices that apply to their jobs, as well as on the overall plant programs for dust control and ignition source control.
A heightened awareness of the hazards of combustible dusts is the first of many steps in everyone working together to prevent further injury and deaths to workers.
The National Institute for Occupational Safety and Health (NIOSH) in the U.S. has published a hazard alert, "Preventing Asthma and Death from MDI Exposure During Spray-on Truck Bed Liner and Related Applications" to raise awareness of isocyanates as a significant workplace hazard.
This alert summarizes reports from four incidents - one of them fatal - of asthma or other respiratory disease that resulted from exposure to methylene bisphenyl isocyanate (MDI) during spray-on truck bed lining operations.
According to CCOHS' CHEMINFO, people who are sensitized to MDI react to very low levels of exposure that may have no effect on unsensitized people. The symptoms may initially appear to be a cold or mild hay fever, however severe asthmatic symptoms can develop (wheezing, chest tightness, shortness of breath, difficulty breathing and/or coughing). Fever, chills, general feelings of discomfort, headache and fatigue can also occur. Symptoms can occur at any time - immediately after the exposure or even much later. Typically the asthma improves when the exposure is removed (e.g. weekends and vacations) and returns, in some cases, as an "acute attack", when the person is once again exposed to MDI. This means sensitized workers cannot be exposed to the chemical in the workplace nor anywhere else. In sensitized people, any exposure to MDI can trigger a severe life-threatening asthmatic response.
Following removal from exposure, some workers may continue to have persistent respiratory problems such as asthmatic symptoms, bronchial problems and hypersensitivity to MDI. Others may recover fully and may gradually lose their sensitivity within several years.
The NIOSH alert is targeted to workers, employers, small business owners, doctors and other health care providers, who need to know how to prevent potentially fatal levels of exposure.
The spray-on truck bed lining process, which is similar to undercoating, involves applying a protective polyurethane or polyurea coating to the bed of pickup trucks or other vehicles and surfaces. Several of these spray-on products, containing isocyanates such as MDI, have been developed for a wide range of retail, commercial, and industrial uses. They are used to protect cement, wood, fiberglass, steel, and aluminum surfaces such as truck beds, trailers, boats, foundations, and decks.
Isocyanates are widely recognized as a leading cause of occupational asthma. Most cases of MDI exposure occur by inhalation of the vapour or aerosol. Exposure is also possible through skin contact during the handling of liquid MDI-based products.
Manufacturers and distributors of products containing MDI and other isocyanates should work together on procedures and controls for the spray-on bed liner process. These should include product substitution, equipment and formulation modification, spray enclosure and ventilation design, work practices, ventilation system capabilities, ventilation maintenance, spraying in enclosed areas, worker isolation, exposure monitoring, and respiratory protection.
The ultimate goal, which NIOSH aims to promote through its Hazard Alert, is for industry to minimize MDI concentrations within the spray enclosures by implementing these procedures and controls, together with respirator use and a written respirator program. Once workers are fully trained in these procedures and controls, the risk of harmful exposure will be greatly reduced.
The words "risk" and "hazard" are among the most commonly used terms in the field of occupational health and safety (OH&S). However the difference between a risk and a hazard is not always clear. To help eliminate confusion in this area, the OSH Answers website produced by the Canadian Centre for Occupational Health and Safety (CCOHS) includes a document that spells out the difference. Here is a summary of that document.
"Risk" and "hazard" are sometimes - misleadingly - used interchangeably. One dictionary even defines a hazard as "a danger or risk," hence the confusion. There is a clear difference, however, between a risk and a hazard.
In the context of OH&S, a hazard is anything with the potential to cause damage, harm or adverse health effects under certain conditions in the workplace. A risk is the likelihood or probability of that happening.
One might say: "Flammable liquids are a safety hazard (because they could cause a fire)", and
"There is an increased risk of fire in a facility containing flammable liquids."
Here's another example. When referring to cigarettes as a health hazard, one could describe the risk as "x number of smokers per 100,000 will likely develop lung cancer" or "cigarette smokers are x times more likely to die of lung cancer than non-smokers." These sorts of statements illustrate that smoking cigarettes (the hazard) increases the risk (likelihood) of lung cancer, a potentially fatal disease.
Workplace hazards come from a wide range of sources. A hazard may be an object (such as a sharp knife), a substance (such as a toxic chemical, e.g., asbestos), a source of energy (such as electricity), a condition (such as a wet floor), a process (such as welding), or a practice (such as hard rock mining). These are considered hazards because they can cause harm. Knives cause cuts; asbestos exposure may cause mesothelioma, a wet floor can cause a slip or fall, and so on.
Practices or conditions that could release uncontrolled energy are also considered workplace hazards. For example, an object that could fall from a height is considered a hazard, because the fall, caused by potential or gravitational energy, could seriously harm whatever of whomever the object lands on. The potential release of compressed gas or steam, caused by pressure or high temperature, is another example of this type of hazard.
Remember that a hazard is something with the potential to cause harm (injury, illness or other adverse health effects). It doesn't necessarily always cause harm. The risk of this happening depends on several "risk factors" such as what hazards are present, the method, frequency and degree of exposure to the hazard, what kind of effect could result, and the likelihood and severity of the potential harm.
According to Ontario's Workplace Safety and Insurance Board (WSIB), last year in Ontario just under 350 workers lost their lives due to injuries and illnesses, and more than 277,000 suffered from injuries or illnesses in the workplace. Some people would label these as "accidents".
But the WSIB is sending out a strong message that in the workplace, there is no such thing as an accident. Each of these so-called workplace "accidents" could have been prevented.
In a new social marketing campaign launched this October, the WSIB wants to change the way people think. The message: Workplace injuries and fatalities are unacceptable, intolerable and 100% preventable. With the aim of making Ontario's workplaces the safest in the country by turning awareness into action, the campaign is spreading the word via television, print, transit, outdoor and website advertising.
An important component of this new campaign is the launch of an extensive new website, www.prevent-it.ca, which presents information about the prevention of workplace injuries and illnesses. In a unique and creative way, the site informs employees, supervisors, workers, health and safety committees, teachers and parents of their rights and responsibilities for workplace safety.
The "Prevent-it.ca" web site is divided by sections with catchy, self-explanatory headings. For example, a section called "Watch-it" contains downloadable files of previous WSIB ads and campaigns. "Experience-it" provides testimonials from people whose lives were affected by dangers in the workplace. The "Learn-it" section lists health and safety resources and features an interactive "bookstore" with hot topics and statistics. "Get-it" is another resource section with safety checklists, tools and more. Web visitors can even spread the word by e-mailing a form to their colleagues, supervisors and friends, from the "Spread-it" section of the site.
Preventing workplace injuries is the responsibility of everyone - including workers, employers, supervisors, health and safety committee members, parents and teachers.
Labour training centres have been making workplace learning a reality for workers across the country and around the world for some time. These training centres strive to help workers improve the skills they use on the job as well as provide them with information that will help keep them safe and healthy at work.
Now there is a program that offers help to the helpers - the labour training centres that are dedicated to helping workers. The Labour Support Program from the Canadian Centre for Occupational Health and Safety (CCOHS) is designed to meet the training and informational needs of the labour community. The program includes a collection of four credible environmental and occupational health and safety databases, selected and priced specifically for labour training centres as well as union members with health and safety responsibilities.
The Labour Support Program is offered exclusively to labour training centres as a tool to educate trainees about occupational health and safety and the importance of a safe and healthy working environment. This program includes access to four important resources including MSDS, CHEMpendium, RTECS® and OSHLINE® with NIOSHTIC® /NIOSHTIC-2.
Together these databases provide information on a broad range of environmental and occupational health and safety topics including occupational hygiene, hazardous chemicals, human health effects of substances, WHMIS, hazard communication, toxicology and case studies.
Specifically the program offers
- Authoritative and reliable information, gathered from the world's most trusted OSH and environmental health sources
- Training opportunities for workers with occupational health and safety responsibilities
- Powerful cross-database search capabilities
- Access to up to date references to OSH literature and chemical information
- Easy and efficient downloading, printing, and record marking
In keeping with CCOHS' commitment to make access to these health and safety resources widely available and affordable, the annual subscription fee of $1,195 (includes unlimited access per location) represents a fraction of the full value of the individually purchased databases - a huge savings. Finally, help for the helpers!
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The Health and Safety Report, a free monthly newsletter produced by the Canadian Centre for Occupational Health and Safety (CCOHS), provides information, advice, and resources that help support a safe and healthy work environment and the total well being of workers.
© 2017, Canadian Centre for Occupational Health and Safety
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