What are an arc flash and flash fire?

Fire Resistant workwear brands are relied upon to provide the safest protection against onsite hazards, including low light sources, intense heat, open arcs, chemicals, or static hazards on Australia’s most danger-prone sites. Perhaps most importantly, FR workwear protects against ‘flash fire’ and ‘arc flash’ events which, although avoided, when occur can be fatal. Understanding the risk and potential for injury will assist in assessing the need for protection.

Arc Flash

An Arc Flash is the light and heat produced as part of an arc fault, a type of electrical explosion or discharge that results from a connection through the air to the ground or another voltage phase in an electrical system. A simple example is when an incandescent light bulb burns out, the filament breaks, and an arc is sustained across the filament, enveloping it in plasma with a bright, blue flash. The temperatures of an arc flash can range from 2,800ºC – 19,000ºC (the sun’s surface is 5,600ºC).

A common term to use is an ‘arc blast.’ Arc flash and flash blasts may sometimes be used interchangeably, but arc flash and arc blast are generally understood as separate byproducts of the explosion. ‘Arc flash’ refers to the cause, and the term ‘arc blast’ refers to the effect of the ‘arc flash’. A short circuit or arc flash can often cause an arc blast, a highly dangerous electrical explosion.

In addition, pressure waves generated by an arc flash explosion can carry a force up to thousands of pounds per square inch, which is powerful enough to knock down or throw nearby workers, and cause damage to the eyes, eardrums, lungs, brain, and other organs. These pressure waves are commonly known as an ‘arc blast.’ The force created from the blast can exceed a ‘tonne’ of pressure per square inch and can be fatal up to distances of 3 meters.

Two thousand people are admitted to burn centres with severe arc flash burns each year. Although not common in Australia, EnergySafe and WorkSafe push strict safety guidelines to be upheld and maintained on the industry frontline.

Flash Fire

A flash fire is a sudden, intense fire caused by the ignition of a mixture of air and a dispersed flammable substance such as a solid (including dust), flammable or combustible liquid (such as an aerosol or fine mist), or flammable gas. Flash fires are characterised by high temperatures of around 500ºC-590ºC and a rapidly moving flame front.

Because the rapidly-moving flame front quickly consumes the dispersed fuel, flash fires are also very brief in duration - typically three seconds or less in any location where a worker may be standing. Among others, this type of hazard is present in oil & gas and chemical manufacturing settings and manufacturing environments where combustible dust can accumulate.

Potential Injuries 

Arc flash is a potentially fatal hazard that can otherwise result in serious injury. Unfortunately, arc flash can occur at any time. It is generally assumed that arc flash only occurs in high voltage situations, but low voltage installations also bring risk due to longer fault clearing times involved in the clearing of high prospective energy level faults. Operators are at most risk of experiencing an incident when conducting high-risk activities such as racking circuit breakers. 

The amount of exposure a person can experience is expressed in incident energy and measured in units of calories/cm2. Any PPE worn by the operator must protect against the expected incident energy of a modelled potential arc flash event. 

When an arc flash event occurs, an operator will be exposed to intense heat and pressure. The plasma ejected from the arc can reach and exceed temperatures of over 5000°C. Clothing that is not fire retardant will ignite, leaving the wearer with severe, potentially fatal burns. 

The explosive pressure causes debris of vaporised metals in the form of molten rock to plummet through the air at speeds exceeding 1120km/hr. Additionally, high pressure may leave an operator with burst eardrums or collapsed lungs, with deafening sound waves greater than 140dB and pressure waves greater than 1.5 tons/m2.