Arc Flash & Electrical Safety

Monday, December 03, 2007

To De-Energize or Not to De-Energize

One of the most important decisions in planning an electric task is whether to de-energize. Whenever possible, live parts to which you might be exposed should be put into an electrically safe work condition, unless your employer can demonstrate that de-energizing creates more or worse hazards, or is not practical because of equipment design or operational limitations.

You might need to work live to avoid interrupting life-support systems, deactivating emergency alarm systems, or shutting down ventilation equipment for hazardous locations, for instance. And de-energizing would not be practical during testing of live electric circuits or work on circuits that are part of a continuous process that cannot be completely shut down.

De-Energizing
An Electrically Safe Work Condition

The most important principle of electric safety is, assume electric circuits are energized unless you make sure they are not. Test every circuit and conductor every time you work on them. The National Fire Protection Association lists six steps to ensure conditions for electrically safe work.

1. Identify all sources of power to the equipment.

2. Interrupt the load current, then open the disconnecting devices for each power source.

3. Where possible, visually verify that blades of disconnecting devices are fully open or that drawout-type circuit breakers are fully withdrawn.

4. Apply lockout/tagout devices in accordance with a formal, written policy.

5. Test each phase conductor or circuit part with an adequately rated voltage detector to verify that the equipment is de-energized. Check the voltage detector before and after each test to be sure it is working.

6. Properly ground all possible sources of induced voltage and stored electric energy (such as, capacitors) before touching. If conductors or circuit parts that are being de-energized could contact other exposed conductors or circuit parts, apply ground-connecting devices rated for the available fault current.

The process of de-energizing is "live" work and can result in an arc flash due to equipment failure. When de-energizing, follow the procedures described below in "Working On or Near Live Circuits."

The above was taken from a NIOSH article that also covers lockout/tagout and information about working on or near live circuits.

Labels: Construction, NIOSH

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Monday, January 22, 2007

Arc Flash Protection In The Mining Industry

Because of the unique requirements of mining the underground mining industry has not been required to comply with NFPA 70E. This has been recognized as a problem because arc flash is a significant source of injuries in underground mining. A report published by NIOSH states:

"Between 1990 and 2003, 2,326 traumatic mine electrical injuries occurred. The largest single category of electrical injury was burns from electrical arcing, which accounted for 893 (38%) of all electrical injuries. Electrical burn injuries of all types accounted for more than 21,500 lost work days."

Why was there such a significant problem. Mainly because arc flash hazards were not recognized as being a problem. The NIOSH report states:

"Findings thus far indicate a general lack of awareness of common arc-flash hazards in the mining industry. Accident reports show that two-thirds of arc-flash injuries involve circuit breakers, cables, hand tools, meters, and plugs. The equipment and PPE needed for safe troubleshooting in arc-prone situations are seldom used. Circuit breakers are often operated beyond their design parameters and many are repaired by third-party rebuilders using substandard components."

As a result NIOSH is creating a program to address arc flash hazards in the underground mining industry. The NIOSH report states:

"This project will produce practical guidelines to determine arc flash boundaries in mines and prep plants. Recommended improvements in work practices regarding the use of hand tools, meters, PPE, and other engineering controls will increase miners’ understanding of arc-flash hazards. Training guidelines will show how to most effectively present this information to the mining audience."

Labels: Arc Flash, Mining, NFPA 70E, NIOSH, Work Place Safety