Arc faults are potentially fatal to any personnel in the vicinity. The intense heat of the arc flash/arc blast can severely burn human skin and ignite the clothing of anyone within several feet of the incident. Treatment for arc flash/arc blast burns can involve years of skin grafts. Without proper eye protection, projectiles and molten debris can cause eye damage.
The intense UV radiation associated with the flash can cause retinal damage. Superheated vapours can injure lungs and impair breathing. The thermos-acoustic blast can damage hearing with ruptured eardrums, cause collapsed lungs and damage other internal organs. The blast can knock personnel off their feet; falls may result in broken bones or lead to electrocution or further injuries on other parts of the system.
It is important to note that the general injury limits for the human body are:
- 2nd degree burns @ 79º Celsius for 0.1 sec.
- 3rd degree burns @ 93º Celsius for 0.1 sec.
- Eardrum damage @ 34.5 kPa
- Lung damage @ 83 kPa
Considering that the temperatures involved in an arc flash/arc blast can exceed 20,000º Celsius, and the associated noise levels can reach 180 dB, the consequences of arc flash/arc blast must not be underestimated.
Arc flash/arc blast PPE
To ensure adequate controls are in place to protect personnel from arc flash/arc blast incident energies, all persons who may be exposed to possible electric shock, arc flash/arc blast or other injury from electrical apparatus must use approved personal protective equipment.
This requires that equipment such as electrical switchboards, panels, motor control centres, that are likely to be operated, maintained, or tested while energised, where the potential for an arc flash/arc blast hazard exists, be labelled with arc flash/arc blast boundaries and PPE requirements. The incident energy level of each item of electrical equipment will determine the appropriate distances at which it is safe to:
- approach the electrical apparatus without wearing arc rated clothing; and/or
- approach and perform electrical work or switching whilst wearing appropriately rated arc flash/arc blast PPE.
The further away workers are from the source of the arc flash/arc blast, the lower the category of PPE they require to protect themselves from such an event. When workers are far enough away from the source of an arc flash/arc blast, they no longer require arc flash/arc blast PPE to protect themselves from the arc flash/arc blast event. This is due to the significant reduction in incident energy, the further away from the arc flash/arc blast source the worker can locate themselves.
An arc flash/arc blast incident energy analysis determines the arc flash/arc blast boundary and the incident energy at a nominated working distance. Where it has been determined that work shall take place within the arc flash/arc blast boundary, PPE shall be selected based upon the arc flash/arc blast analysis and the type of work/activity being performed within the boundary.
