How to give a toolbox talk on arc flash explosions
The US Department of Labor estimates that every day in the United States five to ten arc flash explosions occur on the job. Arc flashes are incredibly violent and devastating to any worker exposed to the instantaneous phenomenon. Most of the time the exposure will result in serious injury or even death. Electrical equipment is designed to withstand up to a certain amount of current. The arc flash occurs when an electrical device suffers very high amount of current within a fraction of a second. Some factors that can cause an arc flash include failure to deenergize components, dust, dropped tools, corrosion, or reduced insulation. Arc flash temperatures can reach 35,000° F, which is 3 times hotter than the surface of the sun. An arc flash also can produce noise reaching 140 decibels, (about as loud as a gunshot) and molten metal shrapnel. Equipment is typically so seriously damaged that it needs to be replaced, which can be very costly to the project or existing structure.
Avoiding arc flash
As a worker you should avoid working on any piece of equipment that is not deenergized. The first and most obvious step in avoiding an Arc Flash Explosion is to turn off the power to the machine before attempting any repair. There are some instances when you’re not able to de-energize the equipment, and in those instances it is imperative to have a Safety Supervisor on site who has experience with electrical safety. The National Fire Protection Association (NFPA) has developed specific approach boundaries designed to protect employees while working on or near energized equipment. These boundaries are:
● Flash Protection Boundary (outer boundary): The flash boundary is the farthest established boundary from the energy source. If an arc flash occurred, this boundary is where an employee would be exposed to a curable second degree burn. The main concern here is the heat generated from a flash that results in burns.
● Limited Approach: An approach limit at a distance from an exposed live part where a shock hazard exists.
● Restricted Approach: An approach limit at a distance from an exposed live part which there is an increased risk of shock.
● Prohibited Approach (inner boundary): This is the distance from an exposed part which is considered the same as making contact with the live part. This distance is not identical among equipment. Some equipment will have a greater flash protection boundary while other equipment will have a lesser boundary.
Outside of deenergizing the systems, the best way to stay safe while working on electrical systems is to be properly trained in what the labeling means and how to apply the information on the equipment. One of the first things OSHA does during a site inspection or an accident investigation is to review the training records for the job site. Lack of training often is cited as a reason for large fines. Unqualified workers must be trained on the hazards of electricity and how to avoid accidents on the job. It’s important for a company to document all training in the eyes of OSHA unless it’s documented it didn’t happen.
As an employee you have certain personal responsibilities while working in dangerous environments. Employees must wear the assigned proper personal protective equipment (PPE), use insulated tools and other safety related precautions. This includes not working on or near the circuit unless you are a “qualified” and trained worker. It’s important that you possess the skills and techniques necessary to distinguish exposed live parts from other parts of electric equipment, in addition to the ability to determine the nominal voltage of exposed live parts, the clearance distances and the corresponding voltages of exposure.
Source: Code Red Safety