Arc flash safety
An arc flash involves a high high-intensity flash and a superheated ball of gas created by electrical arcing. The arc flash is accompanied by very loud noise and molten metal. All of this typically lasts less than one second with core temperature reaching or exceeding 35,000°F.
What causes an arc flash?
It could be accidental contact with the electrical systems, the buildup of conductive dust, corrosion, dropped tools, or improper work procedures.
Five to ten arc flash injuries occur per day in the United States. Injuries often require treatment in a special burn center. Injuries can involve the eyes, hearing, skin, and lungs.
Effective in 2007, OSHA determined that electrical hazards in the workplace pose a significant risk of injury or death to employees and that the requirements in the revised standard would more closely reflect standards found in the NFPA standards.
NFPA 70E (Standard for Electrical Safety in the Workplace) is a standard of the National Fire Protection Association that addresses electrical safety requirements for employees’ workplaces that are necessary for the practical safeguarding of employees.
When are arc flash accidents likely to happen?
Arc flash accidents are more likely to occur when electricians and their assistants are installing or repairing certain types of electrical equipment.
Common causes of arc flash accidents include:
- Dust, impurities, and corrosion at contact
- Sparks produced during racking of breakers, replacement of fuses,
and/or breakers/fuses closing into faulted lines.
- Failure of insulating materials.
- Snapping of leads at connections due to humans, rodents, or birds.
- Accidental touching/dropping of tools, nuts-bolts, or metal parts.
What type of injuries does arc flash cause?
Injuries that can result from an arc flash include burns, skin penetration from flying debris, respiratory system damage, hearing damage, eye and face, and even death.
What is the NFPA standard regarding arc flash?
As a result of the injuries and deaths related to arc flash, changes/additions have been incorporated into the NFPA standards.
1. Only qualified persons shall be permitted to work on electrical conductors or circuit parts that have not been put into an electrically safe work condition.
2. A flash hazard analysis shall be done to protect personnel from the possibility of being injured by an arc flash.
3. Employees working in areas where electrical hazards are present shall be provided with, and shall use, protective equipment that is designed and constructed for the specific part of the body to be protected and for the work to be performed.
4. Personal protective equipment shall conform to the standard given in Table 130.7(C)(8) (reference: NFPA 70E-2004 130.7(C)(8) ©NFPA).
5. Arc Flash Protective Equipment: The entire flash suit, including the hood’s face shield, shall have an arc rating that is suitable for the arc flash exposure.
What is a flash protection boundary?
The closer you approach an exposed, energized conductor or circuit part, the greater the chance of an inadvertent contact and the greater the injury that an arc flash will cause. NFPA 70E-2004, Annex C defines flash protection approach boundaries and workspaces.
When an energized conductor is exposed, you may not approach closer than the flash boundary without wearing appropriate personal protective clothing and personal protective equipment.
IEEE defines “Flash Protection Boundary” as An approach limit at a distance from live parts operating at 50 V or more that are un-insulated or exposed within which a person could receive a second-degree burn.
The radiant energy and molten material that is released by an electric arc are capable of seriously injuring or killing a human being at distances of up to twenty feet.
The flash protection boundary is the closest approach allowed by qualified or unqualified persons without the use of arc flash PPE.
What equipment reduces the risk of arc flash hazard?
There are equipment alternatives that can help reduce the arc flash hazard.
- Metal-Clad Switchgear – Structural design reduces the possibility of arcing faults within the enclosure.
- Arc Resistant Switchgear – EEMAC Standard G14-1 defines the requirements for arc-resistant switchgear, includes robust design and pressure relief vents.
- Current-Limiter Power Circuit Breakers – Reduces the clearing time which reduces the incident energy.
- Current-Limiting Reactors – Reduces the magnitude of fault current which reduces the incident energy.
- Zone Selective Interlocking of Circuit Breakers – Deactivates the preset delay on the circuit breaker closest to the fault, which then trips with no intentional delay.