Electrical Explosion - Arc Flash Blast

In a typical electrical explosion, the tremendous temperatures of the arc cause the explosive expansion of both the surrounding air and the metal in the explosion path. For example, copper expands by a factor of 67,000 times when it turns from a solid to a vapour. The incredible dangers (resulting in physical injury and also death) that is associated with this electrical explosion results directly from the high pressures, intense sound, and penetrating shrapnel that eminates from the explosion. The intense pressure of an Electrical Explosion can easily exceed hundreds or even thousands of pounds per square foot, knocking electrical workers off their ladders. An Electrical Explosion can also easily rupture eardrums, and collapse lungs. The sounds associated with such an electrical explosion can exceed 160 dB. Finally, explosive material and molten metal is thrown out from the explosion zone at speeds exceeding 700 miles per hour. This is certainly fast enough for shrapnel to absolutely penetrate the body.

Simply put, an arc flash is an electrical explosion produced by ionized air and vaporized metal during an electrical fault. Numerous toxic substances are produced as a result of the electrical explosion, which can be inhaled. This in addition to inhaling the intense heat may increase the chance of death. Physical injuries may include:

• Shock Wave
• Blinding light
• Shrapnel
• Intense heat
• Contact with energized components
• Toxic Smoke
• Molten Metal
• Noise Levels
• Hearing Loss
• Falling
• Concussion

Electrical Explosion Occurrance
Each and every day in North America, between five and 10 electrical explosions occur in commercial, industrial and institutional electrical equipment and machinery. Any electical worker who is exposed to such electrical explosions is at significant risk for serious injury or even death.

Arc flash, or electrical explosion, is described by the National Fire Protection Association as “a dangerous condition associated with the release of energy caused by an electric arc.” A sufficient reduction of the electrical insulation or the isolation distance between two energized components is the primary cause of an electrical explosion.

Serious damage to equipment is a likely outcome in an electrical explosion. Sometimes affected equipment is so badly damaged that replacement is the only option. And, of course, the human body is equally capable of being destroyed or irreversibly damaged, with no replacement option.

Components of electrical explosions
Two basic components of electrical explosions:

• Heat Radiation (quantified as “Incident Energy Level”)
• Pressure Wave (also known as “Arc Blast”)

Electrical Explosion Heat
Electric arc temperatures are considered to be approximately 4 times hotter than the sun’s surface. Temperature at arc terminals can reach 35,000°F (for reference, the surface temperature of the sun is ~9,000°F, and the temperature of a wood fire is ~900°F)

Electrical Explosion Heat Radiation

• Heat radiation exposure is a function of:
• Distance to arc
• Available fault current
• Fault clearing time
• Equipment type
• Gap between conductors (determined by equipment)
• Vaporizes metals
• Ignites clothing
• 200 degrees F - skin not curable (the point at which cell death occurs)
• Possible to become fatally burned or seriously injured when working at a distance of 10 feet or more from an electrical explosion.

Electrical Explosion - Personnel Reaction

• Some potential effects on personnel due to Heat Radiation:
• External burns, potentially very severe
• Internal burns, such as to the lungs due to ingestion of vaporized metal and superheated air
• Health effects due to inhalation of toxic gases and heavy smoke due to the burning of paint, insulators, and other components
• Partial or total loss of sight
• Disability
• Death

Electrical Explosion - Pressure Wave
Electrical blast (or explosion) is the result of the rapid expansion of air caused by an electric arc.

• Peaks in the first ½ cycle of fault (~ 9msec)
• Pressure levels of 2,160 pounds per square foot (psf) in the immediate vicinity of the Electrical Explosion have been detected
• Caused by superheating of air and vaporizing of conductors (air expands to roughly 1670 times and copper expands to roughly 67,000 times its volume – i.e. 1 in3 becomes 1.4 yd3)
• Function of arc fault gap and available fault current

During an electrical explosion, molten metal droplets travel as much as 10 feet or more and faster than 700 mph! Expansion produces explosion that results in:

• Molten metal
• Fragmented metal
• High temperatures
• Pressure on the body

Electrical Explosion - Potential effects on personnel:

• Injury due to blast
• Collapsed eardrums leading to partial or near-total loss of hearing and possibly tinnitus – Sound levels of 141.5 decibels at 2 feet from the electrical explosion blast have been detected
• Collapsed lungs
• Injuries due to shrapnel being ejected from equipment
• One positive benefit: can lessen effects of Heat Radiation due to personnel being thrown away from equipment, but this can also lead to other injuries