An arc flash occurs when a flashover of electric current leaves its intended path and travels through the air from one conductor to another, or to the ground.
The hazards resulting from an arc flash incident include burns, extreme heat and fire, flying objects, molten metal, and blast pressure or sound blast. Arc flashes are often violent, and when a human is near the arc flash, serious injury or even death may occur.
In this post, I’ll share some of the information you’ll need to complete an onsite arc flash risk assessment.
The severity of an arc flash injury
There are many things that can cause arc flashes, including:
- Dropping tools
- Accidental contact with particular parts
- Material failure
- Faulty installation
Three factors determine the severity of an arc flash injury: proximity of the worker to the hazard, temperature, and the time it takes for the circuit to break.
Because of the violent nature of an arc flash exposure, employee injuries can be very serious. It’s not uncommon for an injured employee to never regain their previous quality of life and they may also require extended medical care.
The National Fire Protection Association (NFPA) developed specific approach boundaries designed to protect employees working on or near energized equipment. It’s crucial to understand boundary locations before beginning work on equipment, as these define the employees’ potential exposure to an arc flash and the severity of hazards. Therefore, boundaries play a massive role in determining the amount of risk that employees face when conducting their work.
These boundaries, listed from outermost to innermost, include flash protection, limited approach, restricted approach, and prohibited approach. The risk from exposed live parts depends on your distance from those parts.
Exposed electrical components are hazardous, and if workers make contact with wires, terminals, or other parts, they’ll get shocked.
Flash protection (outer boundary)
The flash boundary is the farthest established boundary from the energy source. If an arc flash occurs, this boundary is where an employee would suffer heat exposure. This exposures may cause curable second-degree burns (1.2 calories/cm2). The hazard in this boundary is the heat generated from a flash.
An approach limit at a distance from an exposed live part where a shock hazard exists. The limited approach is the closest an unqualified person can approach, only allowed further if a qualified person accompanies them. A qualified person has received training on the potential hazards and the construction and operation of the equipment involved in a task.
Additional requirements for qualified persons include the skills and techniques necessary to distinguish exposed live parts from other parts of electrical equipment and being able to determine the nominal voltage of exposed live parts. Working on equipment without proper qualification and training severely increases risk.
An approach limit at a distance from an exposed live part in which there is an increased risk of shock. The restricted approach is the closest to the exposed live parts that a qualified person can go without proper PPE (such as flame-resistant clothing) and insulated tools.
When the employee is at the restricted approach boundary, the employee or their tools could touch live parts if the employee is careless with their movements.
Prohibited approach (inner boundary)
A distance from an exposed part that is considered the same as making contact with the live part. The prohibited approach is the distance that the employee must remain from exposed live parts in order to prevent flashover or arcing in the air.
Note: These distances are not the same for all types of equipment. Some equipment will have a larger flash protection boundary, while others will have a lesser boundary. Refer to NFPA 70E for boundary distances at given voltage ranges.
Safety around electrical hazards
To be safe, employees must think about the job and plan controls for possible hazards. The three-step model to follow for optimum safety practices around electrical hazards is recognizing, evaluating, and controlling the hazards.
To avoid injury, the employee must understand and recognize hazards and evaluate the situation by assessing the risks.
Remember: The most effective way to eliminate the risk of electrical shock or arc flash is to de-energize the equipment and not work on equipment that is “live.”
Examples of how the three-step model can protect against electrical hazard risk and arc flash require planning and establishing proper controls. Controls to prevent injury include:
- De-energizing, locking, and tagging out circuits and equipment and not working “live” whenever possible.
- Using proper insulation, guarding, and grounding (including ground fault circuit interrupters (GFCIs)).
- Barricades to warn others of the boundaries.
- Preventing system overloads.
- Reading all arc flash labels to determine the level of PPE required and boundary distances.
Other risk assessment considerations
What makes arc flashes such a common hazard are just how many variables that contribute to them. Below are some additional precautions you can take to reduce arc flash risks in your worksite.
The metal parts of electrical wiring systems that can be touched should be grounded and at 0 volts. When electrical systems are not grounded, metal parts of equipment may become energized.
If a circuit is not grounded, a hazard exists because unwanted voltage cannot be safely eliminated. If a path to the ground is interrupted by nonconductive material, shocks and potential arcing could occur. To minimize the chances of improper grounding, check power tools and outlets before use to make sure they contain a GFCI device. A GFCI will reduce the risk of current leakage.
Overloads in an electrical system can produce heat or an arc. Additionally, wires and other components in a system or circuit have a maximum amount of current that they can carry safely.
If you plug too many devices into a circuit, the electrical current will heat the wires to a very high temperature. This may cause the wires to heat up enough to cause a fire.
If the insulation melts, arcing may occur. Arcing can cause a fire in the area where the overload exists, even inside a wall. To reduce the risk of overloading, check that the associated circuit breakers and fuses are working correctly.
Perform a risk assessment for each piece of equipment operating at 50 volts or more that is not de-energized. Your evaluation should determine the required boundaries and PPE.
Employees must follow the PPE requirements established on arc flash labels. Remember, PPE does not eliminate the electrical hazard or arc flash risk. However, it can help to reduce the severity of an injury.