We usually think of "electrical safety" as avoidance of shock. However, in the industrial workplace, many persons are injured or killed each year without ever contacting energized conductors. Instead, they are victims of the explosive effects of electrical arcs.

Flash burns can be serious at distances of several meters from an arc, the current in which may be 50,000 to 100,000 amperes. Arcing faults are a growing concern because:

1. Economic pressure has reduced the frequency of electrical maintenance and the time allotted to its performance.

2. Personnel cutbacks have reduced the number of experienced technicians

3. Electrical systems are capable of producing higher fault currents.

4. Electrical equipment is aging.

5. Workplace safety standards in general have assumed growing importance in U. S. industry.

New standards deal with arc hazards in several ways. The 2004 edition of Standard 70E (National Fire Protection Association) specifies workspace boundaries defining several degrees of risk and the required distances between workers and energized conductors. An important one is the flash protection boundary at which maximum radiant energy from an arc will cause only curable (second degree) burns. Working within such a boundary requires protective equipment such as face shields or hoods and melt-resistant clothing.

To determine the safe distance, complex calculations in IEEE Standard 1584 (based on extensive laboratory tests) involve electrical system characteristics such as available fault current and protective device clearing time.

A second important consequence of high-power arcing is the blast pressure wave. Explosive pressure on an exposed person can collapse lungs and rupture eardrums, even though the victim may not be burned. That impact can also throw a worker off balance or against a wall to suffer serious injury. As with any explosion, flying fragments of metal can be damaging at even greater distances. A new Fire Protection Research Foundation project has been undertaken to more thoroughly investigate the blast effect.

These standards, applied with caution in conjunction with strong safety training, should reduce the electrical accident rate, But sound system design and maintenance practices remain essential to this effort.

From  "Dealing With Workplace Arc Hazards" ...by Richard L. Nailen, EA Engineering Editor  - 
published in Electrical Apparatus November 2004  © 2004 Barks Publications, Inc.  All Rights Reserved.