Hygiene Stories

When the dust settles

Written by Linda Johnson Wednesday, 01 October 2014 00:00
Dust testing, collection systems can prevent an explosion
 
A large fireball burst through the roof at the northeast side of the mill. The explosion then travelled through the operating and basement levels. Fire spread throughout the premises, completely destroying the mill.

This is how WorkSafeBC described its investigation into an explosion at Babine Forest Products sawmill in Burns Lake, B.C., in January 2012. The investigation determined the cause of the explosion, which killed two workers and injured 20, was accumulation of wood dust. Three months later, a wood dust explosion destroyed the Lakeland Mills sawmill in Prince George, B.C., killing two workers and injuring 22 others.

“When I look at combustible dust in a workplace, I see sticks of dynamite  waiting for their fuses to be lit,” says Raymond Roch, director at the Fire Inspection and Prevention Initiative (FIPI) in Richmond, B.C.

The hazard of combustible dust affects many industries, he says. Most combustible dust incidents occur in wood product companies, but they also happen in industries such as food (egg whites, powdered milk, cornstarch, sugar, flour, grain), metals (iron, aluminum, zinc, magnesium), chemicals (sulphur, pesticides), pharmaceutical, pulp and paper, minerals (coal), utilities, plastics, rubber, printing and textiles.

Dust is combustible when it is flammable or explosive. The fast-burning fire produced in a dust cloud is often called a deflagration. For an explosion to happen, five elements must be present:

• fuel (combustible dust)
• oxygen
• ignition source (a flame, hot surfaces, sparks from electrical equipment or static electricity)
• dispersion (or cloud) of dust particles
• containment of the dust cloud.

Sometimes, there is a series of explosions. The pressure wave created by the first explosion knocks dust off rafters and beams, which then becomes airborne. The fireball from the explosion then lights that dust and causes a secondary explosion, which can dislodge more secondary (or fine) dust and cause another explosion.

“So you get this domino effect,” says Roch. “That’s why you get entire facilities blown up: It wasn’t one explosion.”

If a company is producing dust, the first thing to do is determine whether the dust is combustible. Michelle Murphy, a partner at ioKinetic in Salem, N.H., says every company with dust should get it tested.

“There are some things we know for sure, but they are few.  (We know) sand and salt are not combustible. But for the majority of materials, it’s very difficult to tell,” she says. “So, if you believe it’s not combustible, a quick screening test is a good way to confirm or deny that.”

If a material is combustible, Murphy recommends conducting Kst (explosion severity) and MIE (minimum ignition energy) tests.

The most effective way to prevent an explosion is to control the accumulation of combustible dust, Roch says. One of the most common engineering controls is a dust collection system. It has a capture hood that sucks in dust where it is produced and conveys it pneumatically through ductwork to the dust collector.

According to FIPI, a dust collection system is the most effective way to prevent explosions because it removes from the facility two of the five necessary elements for explosions: dust accumulation and airborne dispersion.

Another engineering control, often used at machine centres and on conveyance systems, is passive containment. To prevent dust produced by equipment or machinery from migrating, it is enclosed and then drops to an area where it is manually picked up.

However, both dust collection and passive containment systems can be hazardous. While they remove the risks of accumulation and dispersion from the general workplace, the systems themselves contain four of the five explosion elements: dust, oxygen, dispersion and containment. It’s essential to eliminate these hazards by providing the system with explosion prevention equipment, proper design to prevent spark generation and regular cleaning of the ducts.  

Another control is wet dust suppression where dust is moistened as it is generated or a mist is sprayed into the air where the dust cloud forms to drop it out of the air. At Lantic, a Montreal-based sugar refinery, water is sprayed on the raw sugar.

“When raw sugar is dumped from a height onto a conveyer belt, it can release a dust cloud. A fine spray of water damps it down,” says Bob Copeland, vice-president of operations.

Building features can help lessen dust accumulation and make surfaces easier to clean. In B.C., Roch says, many companies are removing flat surfaces and making vertical and horizontal surfaces as slippery as possible by using glossy, enamel paint, for example. They are also sealing cracks to prevent dust from seeping in.

There are four key administrative controls: manual housekeeping, safe hot-work procedures, equipment maintenance (to check for loose or vibrating parts and ensure parts are not overheating) and training of supervisors and workers.

A good housekeeping program includes regular cleaning of out-of-the-way places, a fact confirmed by a recent study conducted by the Manufacturers’ Advisory Group (MAG), a safety group whose members include 55 of B.C.’s 140 sawmills.

The study, called the Sawmill Dust Initiative — which was launched in 2012 after the two mill explosions — analyzed 30 sawdust samples from a variety of trees. Ken Higginbotham, project manager of the study, says the results showed wood particles, whether large or small, are more combustible when dried. But even sawdust from recently harvested trees can be combustible if dry enough. The study also found small particles are more combustible and explosive than larger particles or particles of mixed size.

“Smaller materials tend to be more able to float in the air, and the smaller particles are more likely to end up on the beams at the top of the mill or flow down into the basement,” he says. “The study suggested that cleanup efforts need to be carried out everywhere but that particular attention should be made in some of those areas sometimes referred to as secondary, like the beams and the basements. You might not think of those areas as part of your daily cleanup but it’s an important thing to find out.”

Like many organizations in Canada, MAG uses the dust accumulation standard of 3 mm developed by the National Fire Prevention Association (NFPA) in the United States.

“Wherever the dust is, if it’s more than an eighth of an inch (3 mm), it should be cleaned up,” Higginbotham says.

Training should aim to ensure that every employee in the facility — including supervisors, operators, maintenance and even housekeeping staff — has a solid understanding of what a combustible dust is, how the hazard may present itself, how to protect themselves and what to do to avoid the hazards, says Murphy.

At Lantic, training on combustible dust is mandatory for new employees and existing employees receive regular refresher training. Instruction covers situations such as dust in enclosed spaces, raw sugar unloading, icing sugar packaging areas and areas near heat or spark sources.

Workers who are properly educated in dust hazards will also know they can go to management and tell them when a problem needs to be addressed, says Walt Beattie, president of Pottsdam, Pa.-based Beattie Fire Protection and Risk Consulting. Dust explosions usually occur as the result of an upset in the system, and often, as a result of several changes.

“By having an employee step into that chain of events that is setting up for a potential dust explosion and bringing attention to that area so that the overall system can be repaired or modified, that’s going to help them prevent that explosion from happening,” he says.

Ultimately, he adds, all employees should feel empowered to do what is needed to prevent something going wrong, including, if necessary, stopping a process.

With combustible dust, personal protective equipment (PPE) is not very effective, Roch says. If workers must be near a dust cloud, flame retardant clothing and face shields should be worn.

“But PPE is not something we want to see people focus on,” he says. “There isn’t any PPE that’s going to do you any good if there’s an explosion.”

The 2012 explosions affected major changes in the wood industry, Higginbotham says. Companies have invested several million dollars to install misters around machine centres where sawdust is produced. A lot of money has also been spent on collection equipment and on improved ventilation systems to minimize air movement around machines producing dust.

“One thing I’ve learned in 20 years in the industry in B.C. is there’s a very strong and real honesty about wanting to look after employees,” he says. “The explosions were a blow to the industry. But I think there’s a lot to be said for the response of everybody.”
 
Linda Johnson is a freelance writer based in Toronto. She can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it. .

Danger! Ototoxic chemicals

Written by Stefan Dubowski Wednesday, 01 October 2014 00:00
Some solvents can cause permanent hearing damage
 
Dan Tadic, head of the Canadian Welders Association, knows a lot about welder safety. He sold welding equipment for 30 years. Without hesitation, he can rhyme off aspects of the CSA W117.2-01 standard, which covers eyewear, ventilation and other safety measures for welders.

One of those measures speaks to hearing protection. The standard calls on welders to wear personal protective equipment (PPE) to reduce the damaging effects of noise from air carbon arc and plasma arc cutting processes.

“Follow that standard and you’ll have all the equipment you need to work safely,” Tadic says.

But many welders may not be familiar with one emerging occupational health concern: ototoxic chemicals  (substances that have a toxic effect on the ear and its nerve supply). In welding, manganese, a material often present in the fumes that welding creates, is ototoxic. That means if it is inhaled, manganese can harm a welder’s ability to hear clearly.

Ototoxicity is not just a concern for welders but for workers across numerous industries, including printing, boat builders, construction and manufacturing.
  
Harmful to hearing

Ototoxic materials attack the cochlea, the ear’s spiral-shaped cavity and sensing organ that picks up sound. Ototoxic solvents such as styrene, toluene and xylene also affect the auditory vestibular nerve, which transmits sound and balances information to the brain. As well, these substances can harm the auditory cortex, the part of the brain that processes sound.

Damage from ototoxic substances can manifest as different sorts of hearing difficulties. One study conducted by researchers from the University of Queensland in Australia found that members of the Australian Defence Force who were exposed to four or more ototoxic substances were two to four times more likely to experience moderate or severe tinnitus (ringing of the ears) compared to members of the force who were less exposed to the hazardous materials.

In another study, researchers investigating hearing loss among fibreglass and metal manufacturing plant workers exposed to styrene — a material used to make plastic containers and metal products — found that exposure seemed to harm people’s comprehension of spoken phrases.

Researchers at the Université de Montréal conducted a review of studies on ototoxicity and found toluene, a solvent used to make paint and glue, interacts with noise to harm exposed individuals’ hearing even more than either noise or toluene exposure alone. The scientists ranked other substances according to evidence of ototoxicity, too, noting that ethyl benzene, n-hexane and xylene may be ototoxic, and that carbon monoxide may interact with noise to harm hearing. 

Little conclusive evidence

For many of the chemicals, scientists can’t say conclusively that exposure causes hearing loss. Although results from animal testing clearly indicate that certain materials do harm hearing, it’s more difficult to prove that an individual’s hearing loss resulted from ototoxic exposure, especially when exposure to the substance coincided with exposure to noise. Since some chemicals work synergistically with noise to exacerbate hearing loss, it isn’t easy to tell how much of the damage resulted from noise and how much from ototoxicity.

“There are very few things you can say conclusively have an increased risk,” says Bev Borst, technical service specialist at 3M Canada in London, Ont. “Toluene and carbon monoxide are recognized as ototoxic, depending on their concentration. There are others that are of particular interest.”

Adrian Fuente, an assistant professor at Université de Montréal’s School of Speech Pathology and Audiology, sums up the challenge: Scientists can’t expose humans to solvents just to find out how much is too much, say, ethyl benzene. But given the evidence from animal experiments and observed hearing loss among people whose jobs exposed them to ototoxic substances, “it’s very easy to make the link,” he says.

Researchers are working to strengthen evidence of the connection between hearing loss and exposure to ototoxic substances. Thais Morata, member of the hearing loss prevention team at the National Institute for Occupational Safety and Health (NIOSH) in the United States, is deep into this area of research. She says scientists now understand the harmful effects of ototoxicity appear sooner than the effects of noise.

“Investigations which examined the effects of solvents over time indicated that hearing loss is observable two to three years earlier than is usually seen with noise exposure,” Morata says. “This issue of latency is certainly dependent on the ototoxicant and the characteristics of the exposure, and needs further investigation.”

She points to a 1986 landmark study conducted by scientists in Sweden that suggested exposure to ototoxic chemicals is more damaging to hearing than exposure to noise alone. The study looked at the number of insurance claims made for hearing loss from workers in different types of companies. Chemical plant employees made the most claims, even though noise levels at the chemical companies were lower than the noise levels at other businesses.

“Studies conducted with experimental animals have clearly shown that some environmental and occupational toxicants can reach the inner ear through the blood stream,” Morata says. “Some of these chemicals are also damaging to the nerves… What we do not know yet are precise exposure conditions or levels necessary for an effect. The onset, site, mechanism and extent of ototoxic damage from these toxicants vary according to risk factors that include the type of chemical, interactions and exposure level.”

New standard coming

Work on a new CSA standard that identifies ototoxicity as a potential hazard is underway. CSA Z1007 Management of Occupational Hearing Conservation Programs includes information for anyone whose job involves exposure to ototoxic substances and noise. The draft of the standard says managers in such workplaces should submit employees to hearing tests at least twice per year. Borst says Z1007 is expected to be in the public consultation stage before the end of the year and may be published in 2015. It could change between now and then, but for the moment, the draft identifies how workers may potentially be exposed (inhaling, touching or ingesting the substance) and recommends using the right PPE to reduce exposure.

As with any protective gear, compatibility is important. If a worker wears a powered-air respirator with a hood, earplugs would provide excellent fit and protection, Borst says, while earmuffs wouldn’t be compatible.

But protective equipment is the last line of defence against workplace hazards. Morata points out that the hierarchy of controls recommends other solutions first.

“In most cases, the preferred approach is to eliminate the source of hazardous noise or chemical,” she says.

When elimination isn’t possible, substitution of the chemical or the loud equipment for safer alternatives may be the next best alternative. If the hazard can’t be controlled through elimination or substitution, engineering controls may reduce noise at the source. Failing those solutions, companies should reduce exposure through the use of administrative controls, such as changing an employee’s work schedule to avoid the hazards.

While employers face certain responsibilities for employee safety, workers themselves should take steps to protect their hearing health, Morata adds.

“Regardless whether hearing tests are offered at work or not, when one suspects having a hearing disorder, he or she should see a doctor.”
 
Stefan Dubowski is a freelance writer based in Ottawa. He can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it. .

Flour a main cause of occupational asthma: Study

Written by COS staff Tuesday, 30 September 2014 09:47
Flour has been identified as the main cause of occupational asthma in France, closely followed by cleaning products.

Breathing for 2

Written by Stefan Dubowski Monday, 01 September 2014 00:00
Without proper respiratory protection, moms-to-be face risks of birth defects, complications

When Meredith Corman worked at a medical marijuana processing plant in Flin Flon, Man., a few years ago, she wore a surgical mask to keep dried plant particles from entering her lungs. When she became pregnant, she and her employer stepped up the respiratory protection. 

“When the marijuana was dry, I would have trouble with my breathing,” Corman recalls. So managers had her work more on the growing side of the facility and less on the processing side. On the growing side, there was less dust and the work didn’t irritate her lungs as much. Her employer, Saskatoon-based Prairie Plant Systems, also regularly sent inspectors to check the facility’s air quality. Hudbay Minerals, which owned the property, monitored air quality as well. 

Corman’s daughter is now seven years old and in good health. 

Corman and her employer were right to concern themselves with respiratory health. If a pregnant worker has trouble breathing, her fetus may become oxygen deprived. The worst cases can result in a condition known as intrauterine hypoxia and lead to premature birth, low birth rate or cardiac and circulatory birth defects.  

Pregnant workers face these risks in a variety of industries, including pharmaceuticals, health care and mining. 

Breathing difficulties aren’t the only hazard for pregnant workers and their fetuses.  Workers can also inhale dangerous drugs that cause birth defects.  

For example, pregnant nurses who administer aerosolized pentamidine and aerosolized ribavirin to pneumonia patients put their fetuses at risk of developing physiological abnormalities, according to Marion Rita Alex, an associate professor at Saint Francis Xavier University School of Nursing in Antigonish, N.S. Pregnant workers can also inhale dangerous gases. Sandra Dorman, associate professor of human kinetics at Laurentian University in Sudbury, Ont., has studied respiratory dangers for pregnant workers in mining. She says some of the worst hazards come from diesel engines used to power vehicles on mining sites.  

“Some of the byproducts of the exhaust are particulate matter and the particulate is a Class-1 carcinogen. But there’s also carbon monoxide and the nitrogen oxide family. They’re all hazardous.” 

Carbon monoxide is probably “the scariest one,” Dorman says. The gas is common and has an enormous effect on fetal development. She explains that fetal hemoglobin — the substance in red blood cells that carries oxygen — is different from adult hemoglobin. In the fetus, hemoglobin is designed to capture oxygen from the mother’s blood rather than from the air. That enhanced ability to capture applies to carbon monoxide as well, which is dangerous. If a pregnant woman inhales carbon monoxide, the gas is completely concentrated in the fetus.  

“And it takes a long time to unbind, so you’re basically inducing hypoxia,” Dorman says. “In a normally ventilated mining environment, carbon monoxide levels shouldn’t cause significant adverse effects.” 

But if the vents fail or carbon monoxide builds up for some reason, supplied-air respirators, face masks and other personal protective equipment (PPE) can help filter the toxins and allow the worker to get herself and her unborn child to safety. 

Problems with PPE

That said, respirators are complicated for the pregnant worker. 

“(They are) breathing for two,” Dorman says. “They have to bring in more oxygen and expel more carbon dioxide. At the same time, the baby is growing and pressing up into the (mother’s) lungs.”  

As the baby grows, mom can’t draw air as far down into her lungs. This is why women in the third trimester sometimes feel breathless. The condition may be exacerbated if the worker wears a respirator.  

“With a respirator, you may have to generate extra force to breathe,” Dorman says. The harder it is for someone to breathe, the more tired that person’s breathing muscles will become, more quickly.  

“The concern is if you’re fatigued and you don’t take in enough oxygen or push out enough carbon dioxide, it’s going to be worse for the fetus than for the mom.”
 
Respirator fit is another challenge, according to the United States’ Centers for Disease Control and Prevention.  

“Some respirators must be fitted to your face to make a tight seal,” the organization says on its website. “Weight changes, including weight gained during pregnancy, can affect how a respirator fits. If a respirator does not fit correctly, it may not protect you… We suggest talking to your doctor and safety office to make sure you can wear your respirator safely and correctly throughout pregnancy.” 

Sometimes PPE just won’t cut it at all. In 2011 the Canadian Union of Public Employees (CUPE), which represents 474,000 public sector employees across Canada, issued a health and safety bulletin about cytotoxic drugs, which are used in chemotherapy treatment. These drugs may cause tumors and damage or alter DNA. According to the union, the only safe exposure level is zero, and it recommended employers reassign pregnant workers to tasks that don’t expose them to these drugs. 

Speak up sooner

Even if PPE isn’t always the solution, information certainly plays a key role. For instance, although they usually don’t disclose their pregnancies to employers until after the first trimester, women might want to reconsider that common practice. 

“A lot of the critical fetal development occurs in the first trimester,” Dorman says. “That’s the time when the fetus develops its spinal cord, brain and heart, as well as other key organs.”
 
If a pregnant employee’s work involves substances that are dangerous to a fetus, exposure could be especially damaging during those first few months.

Of course, part of the reason a worker doesn’t want to tell her employer before 12 weeks about her pregnancy is that the risk of a miscarriage is high in that time, Dorman notes.  

“You don’t want to tell people you’re pregnant and then have to explain that you’re no longer pregnant in the worst case. Still, I would encourage people to go see their occupational support personnel, such as the hygienist, for advice,” she says. “And I think it’s important for the employer to provide information about who employees can contact to confidentially disclose their pregnancies, so best practices can be implemented immediately.” 

Accommodation

Accommodating pregnant workers need not be difficult. In fact, doing so should be a matter of regular health and safety procedures. That was the situation for Stacey Ritz when she studied at McMaster University in Hamilton. Her PhD research involved examining the molecular and cellular pathways of early allergic responses in the lungs to understand the triggers that lead to allergic disease.  

Part of her work involved extracting RNA from cells and tissues to analyze gene activation. One standard protocol for RNA extraction involves the use of a chemical solution called TRIzol, which contains phenol and chloroform to help separate the various compounds. Phenol and chloroform have adverse effects on the lungs and the central nervous system in humans, and there is some evidence they may increase the risk of birth defects or miscarriage, Ritz explains.
 
So she always used the fume hood when conducting these experiments.  

“When I became pregnant, toward the end of my PhD, I didn’t change my behaviour because we were already taking precautions to protect ourselves from these chemicals.” 

Companies should keep these matters in mind when creating pregnant-worker policies to help ensure employees stay safe and their children arrive without experiencing detrimental effects from damaging gases, drugs and other airborne hazards.  

And what Corman says of her daughter is what every employer wants to hear: “She’s smart, energetic and healthy. I don’t think my work had any effect on her.”
 
Stefan Dubowski is a freelance writer based in Ottawa. He can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it. . 

This article originally appeared in the August/September 2014 issue of COS.


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