Electrical Arc Blast Explosion

By R. W. Hurst, The Electricity Forum

What is Electrical Arc Blast?
The pressure wave created by an arc flash explosion has a force of thousands of pounds per square inch. This is powerful enough to knock down or throw nearby workers and at the same time cause damage to the eardrums, lungs, brain and other vital organs. Arc flash occurs every day in the United States. Molten metal from an arc flash can reach a person in a fraction of a second, capable of pounds per square inch.

Other electrical arc blast effects include:

Searingly high temperatures. The heat and flames generated by an arc blast can reach temperatures of up to 20,000° Kelvin, or 35,000°F. This is enough to vaporize metal components, as well as cause life-threatening (or even deadly) burns to personnel in the immediate vicinity.

Shrapnel from exploded equipment. The explosive force of an arc blast can turn metal objects into high-speed shrapnel, which threaten to seriously injure or kill workers in the general area of the blast.

Damage to eyesight. Arc blasts often create high-intensity light flashes that are capable of causing both temporary and long-term vision problems in personnel whose eyes aren't properly protected.

An Electrical Arc Blast Program is developed by a company in an effort to protect it's workers from exposure to arc fault incidents.

A comprehensive Electrical Arc Blast Program is designed protect electrical workers from arc flash incidents which could cause personal injury and possible death. It includes: an arc blast assessment; and recommendation of Personal Protective Equipment.

An electrical arc blast program dictates what your company must do to comply with the National Fire Protection Association guidelines (NFPA 70E, Chapter 1,11 8 (B)(1) (b), 130.3, and 130.7 (C) (9) (a)) that are being enforced by Occupational Health and Safety Administration (OSHA). The assessment could include: Personal Protection Equipment (PPE) category requirements, labeling recommendations , potential arc flash incident energy levels, determination of protection boundary distances, as well as NFPA 70E interpretation and the application of OSHA requirements to your workplace.

An electrical arc flash explosion and arc blast program study should result in a recommendation to choosing appropriate personal protective equipment (PPE) for worker safety.

Personal protective equipment recommendations for employees working on your electrical distribution equipment
PPE recommendations are based on NFPA 70E, Standard for Electrical Safety Requirements for Employee Workplaces,Chapter 1, Article 130 Edition; and, IEEE Standard 1584, Guide for Performing Arc Flash Hazard Calculations
Short-circuit and protective coordination
Facility electrical single-line diagram

Arc Blast Study Considerations:

A study has not been performed in the past three years
Short-circuit, protective coordination studies on circuit breakers have not been performed in the past five years
Changes have occurred to electrical distribution system or electric utility system
Safety audit is being required
Facility insurance policy is up for renewal
Modifications or expansions of electrical distribution system are being considered

An electrical arc blast program should include:

PPE recommendations presented in clear, tabular format
Written report of findings and recommendations
Optional power equipment labels listing PPE recommendations (for attachment to existing enclosures)
Optional color-coded single line diagram showing PPE recommendations (for posting in electrical rooms)
Optional onsite electrical safety training for electrical workers

So, with all of this information, why do we continue to minimize or ignore electrical safety hazards? Culture seems to play an important role in the perpetuation of these arc flash incidents. The OSHA regulations require employers to provide a workplace free from recognized hazards likely to cause death or serious physical harm to the worker. The best way to remove the hazard is to de-energize the equipment before working on it or to install better protective devices. It is amazing that workers exposed to electrical hazards are not provided the same consideration for their safety and protection as other types of work tasks. For example, workers do not handle harmful chemicals without proper personal protective equipment, but at the same facility the company may expect a worker to perform hazardous electrical tasks without proper protection. Why is there a double standard? The recovery process from this type of injury is long, painful, and, in many cases, the patient is disfigured and has some level of permanent disability. In the human resources aspect of this, the worker’s life is forever altered. This includes his ability to earn a living, have normal physical activities, and in some cases even his relationship with his loved ones is changed forever.