Hard Hats and Jerking Knees....Again
Dave Smith has been an Industrial Maintenance Electrician since 1975. He has taught maintenance, troubleshooting and safety courses to thousands of electricians in mines, mills, refineries, factories, plants, power stations and offshore platforms throughout North America and the Middle East. Dave is a hands-on guy and teache...
April 10 2010
By Dave Smith
My column regarding foam-insert hard hats seems to have created a bit of controversy (EBMag Dec/January 2009/10, “Heads up and hats off with foam inserts”). I received an email from an individual who was concerned my column may be misconstrued. He writes:
I am very worried that your article will [push the electrical community to [a] knee-jerk reaction, and many workers—as you say— [may] exercise the right to refuse unsafe work.
In that column, I advise that when you are wearing a foam-insert hard hat inside the Limited Approach Boundary or Flash Protection Boundary, you should ensure that it has been arc flash or flame-resistant tested. Since there is presently no standard for testing these materials, this cannot be done.
Critics of the video have focused on the fact that it showed a 15-calorie test, claiming it is invalid because, with 15-cal exposure, you would be required to wear Category 3 FR clothing.(Which, by the way, is absolutely correct if you knew you were being exposed to 15 calories of incident energy. If you identify the incident energy as 15 cal, then you definitely need to be in a Category 3 suit with a minimum rating of 25 cal, plus other PPE listed in Table 5, page 48of CSA Z462, “Workplace Electrical Safety”)
But if you thought you were being exposed to a Category 0 HRC (based on the tasks in Table4, page 43, or incident energy below 1.2 cal, as stated on an equipment label), then the present industrial standard is to only wear a hard hat and safety glasses. If that hard hat was of the foam insert variety, you would have a risk.
The first step prior to doing any electrical work is to perform a Hazard/Risk Evaluation (pg 22, 4.1.7.6 and pg 99, Annex F). You need to understand that, when the incident energy at 18 in. from the source of the energy is determined to be 1.2 cal then, as you move closer to the source, the incident energy would— theoretically—increase by the inverse of the distance squared (1 ÷ distance ratio2).
So at 9 in., the distance decreases by half (9 in. versus 18 in.), and the incident energy shoots up to 4.8 cal. At 5 in., the incident energy rockets up to 15.6 cal! These distances are easily achieved when you lean forward to take a close look at something while troubleshooting an energized circuit. When that happens, trust me—your exposure is no longer a mere 1.2 cal.
In addition, when you are working downstream from an older circuit breaker that’s out of spec, you would have no idea: a) how fast that circuit breaker would actually operate, or b) whether it actually can operate.
This means that 33.5% of 34,000 breakers would constitute a serious hazard to any worker working downstream who is also relying on an arc flash hazard study that says 1.2 cal or task tables indicating Category 0. In truth, I am astounded that anyone would be react negatively to that column; it is a slam dunk that you do not wear melting materials on your body when you may be exposed to energized electrical systems. I do not espouse knee-jerk reactions, but I’m all for some kind of reaction... preferably one that leads to action.
But there’s more to do.Arc flash danger is based on time, current and distance, and to turn a 1.2-cal danger into a 15-cal flash, it takes two things: move in closer, and have a poorly operating protective device. Regardless, if it can melt (like the foam insert), keep it away from your electrical systems.
Until next time, be ready, be careful and be safe.©
