Dealing with workplace arc hazards

Electrical Apparatus, Nov 2004 by Nailen, Richard L

The greatest risk is injury or death from faulted apparatus

ELECTRICITY CAN BE DANGEROUS. WHEN REminded of the importance of electrical safety, however, we tend to think only of avoiding shock hazards. The risk of electrocution has always been emphasized, from the earliest days of the choice between alternating and direct current for commercial systems (see "Battle of the Currents," EA October 2003). Also familiar is the danger of fire caused by short circuits in building wiring. Yet in the industrial workplace, the greater risk is injury or death to personnel caused by highpower electric arcs in faulted apparatus.

Arcs are nothing new. The first large-scale use of electricity, nearly 150 years ago, was in arc lighting. An arc's destructive power within switchgear has been known for many years (Figure 1). However, the full range of the arc threat to exposed. electrical workers or equipment operators has only recently come under close scrutiny.

A new emphasis on arcs

Why the new emphasis? Many reasons could be cited. Their relative importance depends upon one's point of view. For example:

* Since the advent of OSHA regulations, workplace safety has assumed greater importance. Litigation and soaring health care costs have played a role in this.

* More has been learned about differences in pathology between electrical burns and thermal burns.

* The stress on reducing equipment downtime, especially in the continuous-process industries, means less opportunity to shut down electrical apparatus for servicing, and therefore more need for work to be performed on and around energized circuits.

* Lengthening of maintenance intervals (typically from one year to two, three, or even more) means increased likelihood of destructive arcing, as well as the tendency to speed up service work.

* Because of greater fault current capability, often accompanied by increased on-site electrical loads without corresponding upgrading of overcurrent protection, arcs have become more powerful and therefore more dangerous.

* Like the nation's electric supply grid, its highway infrastructure, and its power plants, industrial electrical equipment is aging. Much of it is now beyond all normal life expectations.

How big is the problem? Reliable statistics are all but impossible to come by, for a variety of reasons. Various reporting agencies classify "electrical accidents" in different categories. Distinction may or may not be made within the following situations:

* Residential versus industrial premises.

* "Low" voltage (below 600, or below 277) versus "high" voltage."

* Actual contact with energized conductors versus flash burns, injuries, or falls.

* Lost-time or "disabling" injuries versus minor hurts.

* Incidents involving only "electrical workers" (such as members of an electrician's union) versus general employees (mechanics or equipment operators).

According to a 2002 publication of the IEEE Industry Applications Society, "Until recently, there were no good data collection systems in place to collect and analyze" the numbers and nature of electrical accident injuries in the industrial workplace.

From a dozen sources between 1968 and 2003, fatalities from all electrical-related incidents range from fewer than 100 to more than 1,000 annually; injuries of all sorts from 3,400 to 30,000. Many different figures have been quoted by the IEEE, Underwriters Laboratories, the Bureau of Labor Statistics, OSHA, the National Institute of Occupational Safety & Health, the National Electrical Testing Association, the National Fire Protection Association, and various private consultants.

Whatever the correct statistics for injuries, the probability is that from one-third to two-thirds of them are bums. One source has published a figure of 2,000 workers a year sent to burn centers with electrical burns.

In a 1992 IEEE paper, one large petrochemical firm reported an alarming jump in the frequency of "electrical safety incidents" (although not disclosing actual numbers). This is evident in Figure 2, taken from that report. Reasons for the rise in accidents were believed to be retirements and downsizing leading to less electrical expertise and experience in the work force, and reduction in scheduled maintenance. In response, the firm undertook a major safety training program, with considerable initial success as the illustration shows. That work, and some similar efforts elsewhere in industry, led to establishment of the IEEE's annual "Electrical Safety Workshop."

Electrical safety standards

Electrical engineers in the petrochemical industry led the way in creating electrical safety standards during the 1990's. One such document is IEEE 1584 (first published in 2002 and revised the following year), dealing with the phenomenon of "arc flash"-the radiant energy emitted by a high-power arc, which is a leading cause of burns to nearby workers.

This 113-page Guide for Performing Arc-Flash Hazard Calculations is a complex document. It sets forth the following steps:

* Collect data on the electrical system-review the diagrams, physical layout of apparatus, nameplate information, cable routing, protective device usage, etc.