Entering Outdoor Substations, Part 7 of 8
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...
(At the end of Part 6 “Entering indoor substations” in November 2011, Dave explained the importance of knowing escape routes in case of emergency, how to use a fire extinguisher [and knowing which type you’re using], differentiating between high- and low-voltage switchgear, etc.)
Always know where you are to any machine in relation with your body! As you move into the substation, keep your hands and arms close and your body away from the covers of the switchgear. All new switchgear has microprocessor and digital relays, but there are still many substations loaded with electromagnetic relays, and bumping or hitting these – or slamming a door – can cause a substation to trip, so make sure you stay away from the equipment.
You may be there to change the filters in an air-conditioning unit or check a fire alarm. You may be there to collect data from the instrument panel on the switchgear. If you’re going to work in the substation above the equipment, then understand that, should you fall off your stepladder and bump the equipment, it may cause sensitive equipment to trip out.
In many substations, fire alarm systems are located directly above switchgear, and a fire alarm technician has to lean over or step on the equipment. The difficulty there is that you could shake and trigger something and cause the system to shut down.
When you’re in a substation, you want to be there for as little time as possible. There have been instances where the protective gear – the circuit breakers – have tried to clear a fault, failed to do so, and suddenly there’s an explosion in the switchgear. Understand that most installed switchgear is not arc-resistant.
In the last 10 years, new stations have increasingly been built with arc-resistant switchgear, meaning they’re built heavier; doors are heavier, hinges are heavier, with baffles on the top of the switchgear directing any explosion upward.
But when the gear is not arc-resistant, it falls into a grey area. What do you do when the incident energy behind the door is 35 calories (that’s a Category 4 exposure)? What does the door do for you? In an explosion, the door will bulge. The door will blow open under a bigger explosion; and, when the explosion is big enough, it will blow the door off its hinges.
But it is ridiculous to expect you to wear a Category 4 flash suit simply because you’re in a substation. Common practice is this: when you are inside and the doors are closed with properly running equipment, then the Category 4 is behind the door. When you’re gathering data, reading an instrument, turning an ammeter or voltmeter dial (you know… minimally invasive actions), then you do not require Category 4 clothing.
But, when you are actually operating the equipment, you are at a greater risk. At this point it becomes a judgement call. Were a big explosion to happen, a non-arc-resistant door would be blown off its hinges. You would be exposed to 35 calories of incident energy and, were you wearing clothing that is rated for less than that, your clothing could not protect you, and you’re on your way to the burn unit.
In CSA Z462 “Workplace Electrical Safety” and NFPA 70E “Standard for Electrical Safety in the Workplace”, the Task tables describe common tasks, the estimated Hazard/Risk Category (which directs you to minimum PPE required), and whether rubber gloves or tools are required.
Hazard identification is Task based but risk assessment is subjective: is the equipment dirty or clean? Is it old or new? Is it well-maintained and clean, or neglected and contaminated? Is it dry or damp? You can see how subjective risk evaluation can be; however, it may cause you to increase the personal protective equipment (PPE) you are wearing … just to be on the safe side.
Until next time, be ready, be careful and be safe.©