By Richard Douglas
A high voltage arc can happen in less than a second, and the only thing standing between a line worker and this burst of incredible heat and energy is his or her clothing.
It comes as a surprise, then, that there is no regulated standard for the safety clothing of those who work near live wires.
"What we found, is the amount of energy that can be generated by an arc, depending on the size of the arc and the current and so forth, is much higher than a fireman would see in a flash fire," said Ernie Jones, who is involved with creating a new testing standard for the American Society for Testing and Materials (ASTM). "It's considerably higher and it happens in less than a second, whereas the fireman would have about a 20-second time frame to react."
While there are stringent clothing rules for occupations such as fire fighting, the electrical industry in Canada has largely been left on its own.
A different story exists in the United States where regulations from the federal Occupational Safety and Health Administration (OSHA) have made protective clothing a leading issue within the industry.
In 1994 OSHA published its final rule (1910.269) for the electric industry after finding that injuries involving arcs were often worsened by workers' clothing. Its rule prohibited "employees exposed to electric arcs or flames from wearing clothing that could increase the extent of an employee's injuries should an arc occur."
OSHA's rule stipulated certain weights of cotton and wool as appropriate, under certain situations, as were flame retardant and flame resistant (FR) fabrics.
This wording left many in the industry confused as to what would be considered proper clothing for the many different jobs within the industry. Did every employee need to be outfitted with the same FR clothing, or would varying grades of protection suffice in different work areas? The ability to interpret the wording in several ways caused what a clothing manufacturer called a "free-for-all" amongst electric companies scrambling to meet the vague regulation.
Whereas some companies sought to meet the minimum requirements of their interpretation of the ruling, others felt it was an impossible standard to meet and may have purchased clothing that exceeded their needs just to be on the safe side.
(This isn't over yet. OSHA is currently reviewing a new standard for the construction of electrical transmission and distribution lines which again tackles the issue of proper apparel. It should be released by the end of the year.)
And any clothing decision that's made comes with a price tag. Treated natural fibres are generally less expensive than synthetics, but there have been questions about their durability.
For Canadian utilities the choice of protective clothing seems largely based on a mixture of experience, the cost of the fabric and research into testing that has been done.
Keven Jonasson, safety officer for Winnipeg Hydro, said supervisors have been responsible for outfitting their people with clothes made from DuPont's Nomex IIIA aramid fibre.
"It's based on test results and research," he said.
Similarly, the decision to use Nomex-based clothing at Alberta Power was based on worker's experience, said Graham Wilson, manager of health and safety. Flame-resistant clothing has been used by employees there for about five years.
"We didn't have any specific incidents which triggered it, there's just an overall awareness (in the industry) of a need for protection," Wilson said.
Other utilities, such as The Power Commission of St. John, West Kootenay Power and The City of Calgary Electric System rely on clothing treated with Westex's flame retardant.
"We went to it primarily because of cost and performance," said Tom Bestwick, supervisor of safety and environment, City of Calgary Electric System.
And he's happy with that decision. There was recent episode when an employee was exposed to an arc and the clothing proved highly effective.
"We had a primary flash when a lineman lost a tail to an arrester," Bestwick said. "It was approximately 18 inches in front of him. His glasses were pitted and damaged beyond repair. His hard hat was slightly charred. The front of his coveralls were charred, but there was no damage to the clothing underneath or to his skin."
The growth in the U.S. market for FR fabrics, largely due to OSHA, has had a reciprocal effect in Canada. American manufacturers are eyeing this market as a potential for growth. There are number of clothing providers offering brand name fibres - Nomex, PBI - or chemical treatments - Roxel, FR-7A, Proban, Indura - all vying to be the supplier of choice.
Both DuPont's Nomex and Westex's Indura are established names. Others, such as Hoechst Celanese's PBI fibres, are based on proven materials which are now being applied to work wear.
"We don't sell the fabric, we sell the fibre," said DuPont's Earhardt Schumann. "We sell the fibre to weavers who sell it to garment manufacturers."
Nomex IIIA is a blend of three materials that will not burn (unless they are exposed to an environment with a high oxygen, O2, content).
"Nomex is mixed with five per cent Kevlar," Schumann said. "Kevlar adds to the thermal protection in that it doesn't shrink when exposed to high heat and keeps the fabric stable and gives it some extra strength."
A small amount of carbon fibre, about two per cent, is added to make the clothing anti-static.
Westex's Indura, a flame resistant cotton fabric, was introduced in 1989. The company designed it to wear and feel like natural cotton yet be durable. In order to compete with the synthetics, Westex had to ensure its fabric would withstand multiple washings while retaining its flame retardant properties. The Indura process allows the flame retardant to penetrate the inner structure of the cotton fibre which increases the chemical additive's durability. Westex guarantees Indura for the length of its "service life" provided that laundering instructions are followed. Success in this area allows the company to compete with competitors offering synthetic fabrics.
Dan Conrad, of Hoechst Celanese, said his company's PBI fibre has been used since the 1960s, but it's only recently been adapted for safety apparel. A goal for PBI was to echo natural fibres as much as possible without giving up any protection. To that end, the Conrad said PBI fibres have a similar ability to shed perspiration, known as moisture regain, as natural materials.
"This product wears and feels like cotton." Conrad said. "The moisture regain is almost equal to natural cotton."
For those charged with purchasing FR garments for their business, there are questions as to which material, brand name or fibre should be used.
There are two new developments which may make that choice easier.
A new ASTM standard for testing FR fabrics has been adopted, and Ontario Hydro Technologies (OHT) has recently developed a computer program which simulates the effects an arc and offers a guideline to required protection.
ASTM has adopted the first standards for testing FR and untreated fabrics. These provisional standards will be in place for two years as further research is done and then a final standard will be delivered.
"At this point in time these test methods are the only standards that are available," said Ernie Jones, who oversaw much of the testing. "For instance, if you were purchasing fabrics for a utility, you would know the level of exposure line crews could experience. You'd ask for clothing tested to that standard."
The testing standards cover the ignition of basic materials, untreated cottons and wools, and the thermal protection of FR materials.
"(The methodology) is very explicit," he said. "It tells you how to mount the fabrics, what size they are and so forth," Jones said.
The final test standards are based on several years of high current arc tests conducted on the fabrics used in the industry. A majority of the testing has been done at Ontario Hydro's High Current Test Facility in Toronto.
For both standards, fabrics are exposed to thermal energy of arcs of varying strength. The ignition tests, as their name implies, measure the amount of heat energy needed to ignite untreated natural fabrics such as cotton and wool.
For the thermal protection tests, sensors are placed on either side and behind the material, taughtly held by a wooden frame.
"The sensors on each side measure how much energy is imposed on the fabric," Jones said. "The two sensors behind measure the energy that is transferred through the fabric."
The amount of transferred energy is then compared to the Stol Curve, a measurement of how much thermal radiation it takes to burn skin.
These tests are conducted so that at least 20 per cent are above the curve and at least 20 per cent are below it.
"That determines the performance of the fabric according to the ASTM standard," Jones said.
Jones is hopeful this standard could become widely adopted via the International Electric Commission (IEC) and possibly be carried over to a Canadian standard.
Arcpro, the computer program from OHT, is another tool that can be used in choosing the proper FR clothing.
"In order to choose protective clothing for their workers, utilities and industries have to know what the hazard in their particular system or installation is," said Steve Cress of OHT.
And that's where Arcpro comes into play.
"The inputs to the program include things like the current that is available, the distance you might be away from the fault and then gives you a plot of the energy you would be exposed to at various distances from the arc," Cress said.
It also considers such complex variables as gas properties, arc electrode materials, thermal radiation and convective energy dissipation.
By comparing arc model results with clothing properties, the program can help make safety assessments based on a variety of fault arc conditions.
Conrad, of Hoechst Celanese, believes Arcpro will be a help to the industry, but cautions that it must be used with care.
"It does a very nice job of quantifying the heat energy of a particular hazard as long as people at that company can go through and pull through the correct parameters," he said.
And he believes such diligence is ultimately in the company's best interests in this time of cutbacks and downsizing.
"If you value your employ as an individual asset, that value goes way up when you reduce your head count
by 25 to 30 per cent," Conrad said. "The training and time invested makes that employee even more
valuable and the need to protect him becomes even greater."