To work safely with electricity, the Center for Construction Research and Training says that every job should be planned out in advance.

• Decide on your approach and step-by-step procedures. Write down first-time procedures, and discuss hazards before starting the job. Employers should have or develop a permit system for working on live circuits, if a circuit must be worked on live.

• Identify the hazards. Do a job hazard analysis and identify steps that could create electric shock or arc flash hazards.

• Minimize the hazards. De-energize the equipment or insulate or isolate exposed live parts so you cannot contact them. If  this is impossible, get proper personal protective equipment (PPE) and tools.

• Anticipate problems. If it can go wrong, it might. Make sure you have the right PPE and tools for the worst-case scenario.

• Get training. Make sure you and everyone working with you is a qualified person with appropriate training for the job.

An arc flash is the sudden release of electrical energy through the air when a high–voltage gap exists and there is a breakdown between conductors.

According to the National Institute for Occupational Safety and Health (NIOSH), an arc flash gives off thermal radiation (heat) and bright, intense light that can cause burns.

High–voltage arcs can also produce considerable pressure waves by rapidly heating the air and creating a blast. This pressure burst can hit a worker with great force and send molten metal droplets from melted copper and aluminum electrical components great distances at extremely high velocities.

An arc flash can be spontaneous or result from inadvertently bridging electrical contacts with a conducting object. Other causes may include dropped tools or the buildup of conductive dust or corrosion.

Conditions under which arc flash can occur include working on an energized circuit and electrical equipment failure.

NFPA 70E requires the establishment of an “electrically safe work condition” before working on a circuit by deenergizing it. This can be done by (1) identifying all power sources, (2) interrupting the load and disconnecting power, (3) visually verifying that a disconnect has opened the circuit, (4) locking out and tagging the circuit, (5) testing for voltage, and (6) grounding all power conductors.

Use a written permit system for planning and conducting work on or near energized parts. Use tools, meters, and other equipment suitable for the voltage and current levels present when performing all electrical work.

Employers and safety managers have the responsibility of preventing arc flash injuries. They must provide a safety analysis of the workplace and develop engineering controls to eliminate hazards.

One of the most important decisions in planning an electric task is whether to deenergize. Whenever possible, live parts to which you might be exposed should be put into an electrically safe work condition, unless your employer can demonstrate that deenergizing creates more or worse hazards, or is not practical because of equipment design or operational limitations.

You might need to work live to avoid interrupting life-support systems, de-activating emergency alarm systems, or shutting down ventilation equipment for hazardous locations, for instance. And de-energizing would not be practical during testing of live electric circuits or work on circuits that are part of a continuous process that cannot be completely shut down.

The most important principle of electric safety is, assume electric circuits are energized unless you make sure they are not.

Test every circuit and conductor every time you work on them. The National Fire Protection Association lists six steps to ensure conditions for electrically safe work.

• Identify all sources of power to the equipment.

• Interrupt the load current, and then open the disconnecting devices for each power source.

• Where possible, visually verify that blades of disconnecting devices are fully open or that drawout-type circuit breakers are fully withdrawn.

• Apply lockout/tagout devices in accordance with a formal, written policy.

• Test each phase conductor or circuit part with an adequately rated voltage detector to verify that the equipment is de-energized.

Check the voltage detector before and after each test to be sure it is working.

• Properly ground all possible sources of induced voltage and stored electric energy (such as, capacitors) before touching. If conductors or circuit parts that are being de-energized could contact other exposed conductors or circuit parts, apply ground connecting devices rated for the available fault current.

The process of de-energizing is considered “live” work and can result in an arc flash due to equipment failure.

Working on live circuits means actually touching energized parts. Working near live circuits means working close enough to energized parts to pose a risk even though you may be working on de-energized parts.

Common tasks where you need to work on or near live circuits include:

• Taking voltage measurements;

• Opening and closing disconnects and breakers;

• Racking breakers on and off the bus;

• Removing panels and dead fronts; and

• Opening electric equipment doors for inspection.

There should be standard written procedures and training for these common tasks.

For instance, when opening and closing disconnects, use the left-hand rule when possible (stand to the right side of the equipment and operate the disconnect with your left hand). For other situations where you might need to work on or near live circuits, employers should institute a written live work permit system which must be authorized by a qualified supervisor.

A live work permit should, at a minimum, contain this information:

• A description of the circuit and equipment to be worked on and location;

• The date and time covered by the permit;

• Why live work will be done;

• Results of shock hazard analysis and determination of shock protection boundaries;

• Results of flash hazard analysis and determination of flash protection boundary;

• PPE to be worn and description of safe work practices to be used;

• Who will do the work and how unqualified persons will be kept away; and

• Evidence of completion of job briefing, including description of job-specific hazards.

The National Fire Protection Association defines three approach distances for shock hazards and one for arc flash.

• The limited approach boundary is the closest distance an unqualified person can approach, unless accompanied by a qualified person.

• The restricted approach boundary is the closest distance to exposed live parts a qualified person can approach without proper PPE and tools. Inside this boundary, accidental movement can put a part of your body or conductive tools in contact with live parts or inside the prohibited approach boundary.

To cross the restricted approach boundary, the qualified person must:

(a) Have a documented plan that is approved by the manager responsible for the safety plan.

(b) Use PPE suitable for working near exposed live parts and rated for the voltage and energy level involved.

(c) Be certain that no part of the body enters the prohibited space.

(d) Minimize the risk from unintended movement, by keeping as much of the body as possible out of the restricted space; body parts in the restricted space should be protected.

The prohibited approach boundary is the minimum approach distance to exposed live parts to prevent flashover or arcing. Approaching any closer is comparable to making direct contact with a live part. To cross the prohibited approach boundary, the qualified person must:

(a) Have specified training to work on exposed live parts;

(b) Have a documented plan with proper written work procedures justifying the need to work that close;

(c) Do a written risk analysis;

(d) Have (b) and (c) approved by the manager responsible for the safety plan; and

(e) Use PPE appropriate for working near exposed live parts and rated for the voltage and energy level involved.

The flash protection boundary for arc flash is the distance at which PPE is needed to prevent incurable burns (2nd degree or worse) if an arc flash occurs.

For systems of 600 volts and less, the flash protection boundary is four feet, based on an available bolted fault current of 50 kA (kiloamps) and a clearing time of 6 cycles (0.1 seconds) for the circuit breaker to act, or any combination of fault currents and clearing times not exceeding 300 kA cycles. For other fault currents and clearing times, see NFPA 70E.

Remember, when you have de-energized the parts you are going to work on, but are still inside the flash protection boundary for nearby live exposed parts: If the parts cannot be de-energized, you must use barriers such as insulated blankets to protect against accidental contact or you must wear proper PPE.

When working on or around live circuits, be sure to wear the right PPE to protect against electric shock and arc flash.

Never wear clothing made from synthetic materials, such as acetate, nylon, polyester, or rayon – alone or combined with cotton.

Such clothing is dangerous because it can burn and melt into your skin. The type of PPE worn depends on the type of electric work being done. Once the hazard/risk category has been identified, check requirements for clothing and other PPE when working on or near energized equipment within the flash protection boundary. These PPE requirements protect against electric shock and incurable arc-flash burns. They do not protect against physical injuries from arc blasts. FSM