Electric Arc Flash/Blast Hazards

Electricity is widely recognized as a deadly workplace hazard, exposing employees to electric shock, bums, fires, and explosions. According to the Bureau of Labor Statistics, 289 employees were killed in 2002 by contact with electric current. Other employees have been killed or injured in fires and explosions caused by electricity.

Bums suffered in electrical accidents can be very serious. Bums are usually one of three types: electrical bums, arc bums, and thermal contact bums. This topic is concerned with the second type-arc bums. In its basic terms, an arc flash is a short circuit and air is the conductor. Arc faults are similar to arc welding. Arc bums are the result of high temperatures produced by electric arcs or by explosions close to the body. If the current involved is great enough, these arcs can cause injury or can start a fire. Arc bums are similar to bums and blisters produced by any high temperature source.

Fires can also be created by overheating equipment or by conductors carrying too much current. Extremely high-energy arcs can damage equipment, causing fragmented metal to fly in all directions. In atmospheres which contain explosive gases or vapors or combustible dusts, even low-energy arcs can cause violent explosions.

Nature of electrical accidents.The underlying cause of electrical accidents is a combination of three possible factors: 

, Work involving unsafe equipment and installations.

, Workplaces made unsafe by the environment.

, Unsafe work performance (unsafe acts).

Summary of the NFPA 70E regarding protection’s from arc flash/blast 

• The NFPA 70E requirement for determining if lockout/tagout can be used to make circuits/equipment safe before implementing PPE requirements is similar to the OSHA requirement.
• The 70E requires a "work permit' when working on energized electrical components. OSHA does not require this work permit.
• The 70E requires a "shock hazard analysis' and "shock protection boundaries." This requirement is similar to approach distances to electrical equipment outlined in the OSHA regulations.
• The 70E requires a "flash hazard analysis" to establish "flash protection boundaries." The OSHA requirements are set in "feet from the hazard" depending on the circuit/equipment voltages.
• The 70E has requirements for work on or near uninsulated overhead lines. The OSHA requirements are similar.
• For the 70E, the employer has the option of doing the "flash hazard analysis' and providing appropriate PPE or classifying the hazard/risk according to the specific activity. The standard provides a chart of typical activities and the hazard/risk category of that activity. The chart also determines the appropriate voltage rating of gloves and tools.
• The NFPA 70E provides a protective clothing and personal protective equipment matrix to determine the appropriate clothing, eye/face, hand, and foot protection according to the hazard/risk category. Are your workers trained?