An arc flash is an electrical explosion that occurs when electricity short circuits through the ground or air to another phase. The resulting flash can see temperatures of more than 35,000°F, which is hot enough to melt and vaporize copper conductors and anything in the immediate area. When copper is vaporized, it expands in size by a magnitude of tens of thousands. This, in combination with acoustical and thermal energy, results in a pressure wave and propelled debris that can be fatal.
NFPA 70E requires that an employer conduct an arc flash risk assessment to determine the risk, labeling requirements, required work practices and procedures, insulated tools needed to do work on the systems, what PPE is required, and to determine arc flash boundary areas.
(Learn more in Electrical Safety Basics: A Guide to NFPA 70E.)
The safety way to work on an electrical system is to de-energize it prior to any work, maintenance, or inspection. However, this is not always be possible and other control methods need to be in place to keep employees safe.
But first, you need to know whether there is a risk of arc flashes in your workplace to begin with. Here are a list of questions to help you determine whether that is the case – and what to do if it is.
- Is an arc flash study necessary?
- Does anyone in the organization have the expertise to determine whether there is an arc flash hazard in the workplace, or will the company need to bring in an outside consultant?
- Are there sufficient time and resources to conduct an arc flash risk assessment in house?
- Who should be placed on the arc flash risk assessment team?
- What are the best practices when conducting an arc flash assessment?
- Which pieces of equipment in the facility have potential for arc flash to occur?
- What type of work could potentially expose workers to arc flashes?
- What is the likelihood of it occurring?
- What is the equipment's design?
- Operating time?
- How long does it take to close?
- Its overcurrent protective devices?
- Its condition?
- Are the maintenance programs sufficient?
- Are there conditions that can amplify the size and energy?
- What are the workplace conditions that can contribute to an arc flash?
- What is the potential severity?
- What is the voltage?
- What is the amperage?
- What is the arc gap?
- What is the distance from
the arc?
- What is the opening time of the overcurrent device?
- How much thermal energy can be released during an arc flash?
- How can I calculate incident energy using fault current, system voltage, clearing times of over-current protective devices, and parameters of the electrical system?
- How can an arc flash occur in my workplace?
- Are there gaps in the insulation?
- Is there corrosion, impurities, or other particles on the surface of a conductor?
- Could dropping a tool ignite an arc flash?
- Is there a risk of a spark that could ignite an arc flash?
- Could something come too close to a conductive course?
- How much wear and tear is there on the equipment and conductors?
- Are there improper or inadequate parts?
- Was the insulation done properly?
- What is the arc flash boundary?
- Which calculations and methods do I use to determine the arc flash boundary?
- What working distances are required in which the energy level does not exceed 1.2 cal/cm2?
- What procedures and processes do we need in place to prevent potential arc flashes?
- Can we eliminate the hazard altogether?
- Can we engineer out the hazard?
- What training is required?
- What are the ANSI Z535 labeling requirements and does the equipment meet them?
- Which equipment needs to be labeled?
- Machines?
- Panels?
- Switch boards?
- Control panels?
- Socket enclosures?
- Motor control centers?
- Where should the labels be placed?
- What information, statement, and pictogram do the labels require?
- What if the electrical equipment is updated?
- Which insulated tools are required?
- What are the arc flash PPE rating requirements and what method will be used to determine the appropriate PPE? (Incident energy analysis? Arc flash PPE category?)
These are a some of the major questions you should ask to determine whether there is an arc flash risk in your workplace. There are established standards and guidelines for arc flash protection developed by power systems engineers. Following those will prevent injuries and damage to equipment.
For more information, refer to: