Source: www.ohscanada.com

THE CANADIAN NATIONAL EXHIBITION (CNE) in downtown Toronto brings to mind fun rides, cheesy games and the unofficial end to summer. But the midway grounds were the site of a far less celebratory experience several years ago.

On August 17, 2005, two workers were at an electrical substation on the CNE grounds investigating the source of a partial power loss to a concession stand when there was “an electrical explosion,” Ontario’s Ministry of Labour reported at the time. One worker was using a screwdriver to pry a fuse from a switch terminal when the incident occurred. His clothes were set ablaze, resulting in second-and third-degree burns to both employees.

Neither worker had been provided or was wearing personal protective equipment (PPE).

A ministry investigation later revealed that the worker using the screwdriver had turned an external switch door handle to the “off ” position, but an internal switch mechanism remained “on”. The screwdriver’s contact with the fuse caused a live electrical path at the switch terminal that resulted in the explosion. The employer was levied a $100,000 health and safety fine for failing to provide PPE to workers.

“Most people are very familiar with the concept that highvoltage circuits can have a potential for a shock hazard. People are generally less familiar with the idea that circuits with high amperage have the potential for arc flash,” explains Randy Templeton, senior technical marketing specialist for DuPont Canada in Mississauga, Ontario.

Hot, hot, hot

Templeton describes arc flash as “essentially a fireball” created in less than a second (sometimes as little as one-tenth of a second) when a substantial amount of electrical current passes through ionized air. Approximately half of electrical accident injuries are burn injuries, he estimates, not shock-related incidents.

Mike Doherty, president of Blue Arc Electrical Safety Technologies Inc. in Oshawa, Ontario, concurs, pointing to statistics out of the United States that show “there are 10 workers every day, seven days of the week, 365 days of the year, that go to the hospital for arc flash burns.”

Fireballs can produce temperatures as high as 35,000 degrees Fahrenheit — that’s about four times the temperature of the surface of the sun.

Andy Kerr, a health and safety consultant with the Electrical & Utilities Safety Association (EUSA) in Mississauga, Ontario, likens arc flash to gunpowder going off, spraying hazardous materials 360 degrees. Arc flash may also create secondary hazards, such as hot gases, molten metal splatter, pressure waves, projectiles, highdecibel noise and electrical shock potential.

Such a hazard may result from a number of factors, notes information released by Newfoundland and Labrador’s Department of Government Services. These include dust and impurities, corrosion, water condensation on the surface of insulating materials, spark discharge and insulating material failures, as well as dropping tools, improperly maintained electrical meters, improperly designed or used equipment, improper work procedures and human error.

Sudden stop

However, recent advancements on both the devices and PPE fronts are making their way into the hands of end-users. Devices on some electrical equipment are now available to trip the associated breaker almost immediately, shutting down power, says Doherty, a licensed industrial technician for more than three decades.

Daniel Roberts, national safety manager at Schneider Electric Canada in Mississauga, Ontario, explains there are two components present in every arc flash event: an intense “light” and an increase in electrical current, which is monitored by detectors. When the two conditions are present simultaneously, Roberts says, the electrical equipment/detector is set to interrupt the flow of power.

“Some of these systems are so sophisticated that they can detect, within 1/240th of a second, if an arc flash is developing,” he reports. “The longer [arc flash] goes on, the more it destroys, the hotter it gets, the worse it is for the employee,” Roberts says.

That’s not to say protective devices will completely prevent an arc flash, he points out, just that “it doesn’t allow it to develop its destructive proportions.”

Material matters

That’s where PPE — often viewed as the last line of defence — comes into play. Arc flash protection gear runs the gamut from shirts, pants, outerwear (including jackets, bib overalls, coats and coveralls) to hoods, face shields, goggles and even protective underwear. Popular brands are usually made of inherently flameresistant (FR) fabrics, such as aramid modacrylic blends or FR-treated materials, and may weigh as little as 4.5 to 13 ounces.

Industry experts agree choice of fabric is a key consideration to help ward off the possibility of injury. Templeton notes that fabrics such as cotton, wool or silk will ignite when exposed to these hazards. “At that point, the person is wearing the fire and they will get very severely burned, [because] the clothing cannot be put out in a reasonable time to avoid severe burn injuries,” he points out.

As well, Templeton reports, “fabrics like polyester, cotton-polyester, polypropylene [and] nylon, these fabrics can ignite and/or melt, so that can significantly increase the injury.”

All garments will decompose when exposed to the direct heat of arc flash, he says, but it’s key that the fabric does not ignite. “If you have a cotton garment, where it is exposed to an arc flash, it disintegrates, but the rest of the garment catches fire,” Templeton explains.

Typically, clothing is manufactured to offer protection based on a specific hazard risk category, as identified in the National Fire Protection Association’s (NFPA) 70E Standard for Electrical Safety in the Workplace. The lowest to highest levels of protection are as follows:

• Category 0 requires no specialized protective clothing;

• Category 1 provides an arc thermal performance value (ATPV) rating of four calories per square centimetre (cal/cm2) — the units to measure instant energy from an arc flash;

• Category 2 is eight cal/cm2;

• Category 3 is 25 cal/cm2; and,

• Category 4 provides a rating of 40 cal/cm2.

In most applications, experts agree, employees will require Category 2 protection. Those who work on switchgear — the combination of electrical fuses, disconnects and circuits used to isolate electrical equipment — may require higher Category 4 protection, possibly including visors, goggles and face shields.

While NFPA 70E currently serves as guidance for workplace parties in Canada, a “technically harmonized” Canadian Standards Association (CSA) document is in the works. The Englishlanguage Z462 standard, Workplace Electrical Safety, is set for release this December, followed by a French-language version next March, says Dave Shanahan, CSA project manager.

Gear, however, should not be considered in isolation. The effects of layering garments may prove a critical protective move. Consider a worker who first requires an FR shirt and pants, but may need FR coveralls for specific job tasks. If the shirt has an ATPV rating of 4, but both pants and coveralls have a rating of 8, what would be the rate for the shirt and pants alone or the “system” as a whole?

Well, says Roberts, it could be 4, 12 or 20. Although the rule of thumb is that the total will be greater than the sum of its parts, this is not always the case. Layers need to be tested for ATPV values as an entire system, he cautions.

Layering also serves the purpose of providing air between clothing, which can act as an insulator and help protect workers from more severe injuries.

“You can’t simply go to Joe’s Safety Supply and take off of the shelf various pieces of equipment and add them up yourself,” Roberts says. “The worst thing an employer can do is simply go out and buy equipment and give it to their employee without really understanding why,” he suggests. EUSA’s Kerr recommends that employers use a “multiple barrier” approach. Consider two workers doing transmission distribution work using a dielectrically tested bucket truck, one that has recently undergone a current leakage test by one person. “We’re relying on that truck as a barrier,” he says.

If the workers, wearing rubber gloves, then step into the truck’s bucket, “there’s a second barrier,” Kerr explains. An eight-foot piece of insulated equipment, used when working on an electrical switch, will provide a third barrier.

Despite using multiple barriers and appropriate PPE, problems can still crop up. Andrew Wirts, sales and marketing director for NASCO Industries Inc. in Washington, Indiana, says workers sometimes do not pay attention to their outermost layer of clothing.

For example, he says, a jacket containing polyester or nylon may be worn over an FR shirt.

“What actually happens is the polyester or nylon layer on the outside melts through and can create a heat transfer burn that wouldn’t have been there otherwise,” Wirts explains.

The same potential for more serious injury can result if undergarments, depending on the fabric, are not in line with the conditions. Some manufacturers have taken note, creating arc flash protective undergarments, reports Shawn Brown, vice-president of sales and marketing at Geliget Gear, based in Stellarton, Nova Scotia. “It’s very frustrating for people that are in the industry to hear of instances where people put all the effort and investment into the primary PPE and then to have on polyester-cotton blend underwear,” Brown says.

As with all PPE, comfort comes into play. “Everybody is looking for an opportunity or the way to be able to offer the industrial protection and maintain the recreational comfort and that becomes a struggle,” Wirts says. Many products now on the market are both comfortable and stylish, but still maintain performance requirements, he says.

Unfortunately, Brown cautions that some counterfeit products are also rearing their ugly heads. Some manufacturers, he contends, are substituting off-brand or generic fabrics and “sometimes blatantly counterfeit products,” which bear the logo of reputable vendors. “It’s difficult because the product will look similar or the same,” Brown says. “End-users will assume they are getting a safe product and, unfortunately, the only way to find out is if there is an incident,” he adds.

In some cases of counterfeit PPE, “if that item fails, you’re not going to cause a death or, in most cases, it’s not a life-threatening situation. But in this market sector, it’s a different story.”

One way to protect workers is by respecting “approach boundaries”, spelled out in CSA’s upcoming Z462 standard. Distance from an arc flash incident — along with duration and electrical current — are factors that may have an impact on the degree or severity of an injury, says Roberts. An effective distance is often calculated in “inverse square” terms, meaning that as heat travels from a source (exploding equipment, for example) and the distance doubles, the amount of heat decreases by a factor of four, he explains.

As a safety tip, Roberts offers, “rather than have employees operate equipment standing directly in front of it, could the equipment be remotely operated, thereby increasing the distance of the worker from the potential fault?”

In CSA Z462 (see chart above), approach boundaries are listed in three categories: limited, restricted and prohibited zones, which distinguish between zones for qualified and unqualified workers, as well as shock and arc flash protection boundaries, Roberts says. “The difference between the two is shock protection literally protects the worker from injury; the arc flash protection boundary protects them from destruction,” he says.

A firm understanding of conditions is essential since some misconceptions persist.

People often equate low-voltage electrical exposures with low hazards, Roberts says. “Ironically, in the lower voltages, such as are used in industries and factories, you can end up with higher exposures than you can for utility workers working with very high voltages,” he says.

“You can’t necessarily assume that because this guy is only working in a factory, only working on 600 volts, that it’s going to be a smaller hazard,” Roberts cautions.

Workers usually work closer to low-voltage equipment and farther away from higher-voltage equipment, Roberts says. But current is a key component of arc flashes; there are higher current levels at lower voltages and lower current levels at higher voltages.

In the event of an arc flash incident, Brown says the affected person will likely have been thrown and may be disoriented. “That person is not going to be necessarily in a good position to consider the fact that his clothing may be on fire, his co-worker may be injured,” he says.

The whole situation “can happen literally in the blink of an eye,” Shanahan agrees. “People themselves just cannot react fast enough to avoid being struck by such a flash.”