Prevent Arc Flash with LO/TO

An arc flash can release a deadly blast of energy without any warning, making it one of the more frightening hazards involved with electrical work. Dropping a tool, opening a panel on degraded equipment, and even pest infestations can trigger an arc flash; it's very difficult to predict and prevent them. However, there's one factor that unites all arc flash incidents, and can be controlled: All arc flashes require electrical power.

As a result of this simple fact, the accepted industry standard for safe electrical work (NFPA 70E) recommends a simple approach to completely eliminate the risk of arc flash when working on electrical equipment: Shut it off and lock it out.

The Electrically Safe Work Condition
That's the main idea behind what the NFPA calls an "electrically safe work condition." Generally, NFPA 70E requires an electrically safe work condition in either of these situations:

  • An employee works within the Limited Approach Boundary, a clearance area around equipment designed to prevent unqualified workers form being exposed to a hazard of electric shock
  • A worker faces an increased risk of injury from arc flash as a result of the nature of his work or the equipment being worked on

In both of these cases, the most effective way to protect the worker is to keep the equipment in a de-energized state, with no electrical power. Where there is no power, there is no risk or electric shock or arc flash!

De-energizing the equipment is only part of the electrically safe work condition, though. Imagine you're working on equipment that's been powered down for safety; all of the electrical hazards have been essentially eliminated. Then, another worker enters the room and flips a switch to start working on his own tasks. That could be catastrophic unless you can be certain that the equipment you're working on can’t be accidentally started up again. That certainty is the idea behind lockout/tagout (LO/TO).

LO/TO Steps for Electrical Work
All lockout/tagout procedures follow the same basic ideas:

1. Identify the equipment’s sources of power
2. Shut down the equipment and disconnect those power sources
3. Apply locks and tags to keep the power sources disconnected
4. Confirm that the equipment is completely de-energized

With electrical work, the same basic ideas still apply, but some additional steps may be called for. All affected workers should be informed that equipment will be disconnected temporarily and should be told why this is the case so there is no misunderstanding. Many electrical systems can carry power without any obvious indication that they're still energized, so the NFPA standard requires using appropriate testing tools to confirm the absence of power. If procedures aren't tailored for the actual hazards and situations that are present in a facility, accidents and injuries are going to remain a problem.

The NFPA 70E standard includes an example of an effective LO/TO procedure in Informative Annex G. As experts in safety, NFPA makes recommendations to double-check each critical point in the process. The following steps are based on NFPA's description in that informative annex.

1. Notify all affected employees that equipment is being shut down, and provide the reasons for doing so.
2. Identify all sources of electrical power to the equipment.
3. Shut down the equipment and disconnect any energy sources.
4. Relieve any stored energy appropriately (by grounding, attempting to start the equipment, or other means).
5. Apply locks and tags to all disconnecting devices.
6. Verify that locks are properly applied.
7. Use an appropriate testing tool to verify that the equipment is de-energized and then verify that the tool is functioning correctly by testing a known voltage source.
8. Where necessary, install a grounding device to eliminate the risk of induced or stored voltage.

After this process is complete, the equipment will be in an electrically safe work condition and work may continue.

OSHA's Rules for LO/TO and Arc Flash Safety
While the NFPA standard represents expert advice and industry consensus, it's not strictly required by law. Instead, workplace safety in the United States falls under the jurisdiction of OSHA and its regulations. OSHA's general requirements for safe electrical work practices are in 29 CFR §1910.333, and a basic approach for working on de-energized equipment, including a LO/TO system, appears in paragraph (b) of those rules. These rules generally align with OSHA's more extensive LO/TO rules in 29 CFR §1910.147, which go into more detail about the lockout or tagout devices that should be used.

Because these regulations can be changed or updated only through a long and involved process at the federal agency, it's common for facilities that prioritize safety to look to experts such as NFPA for advice on protecting their workers. In fact, where a given question is not covered by regulations, OSHA frequently uses NFPA standards such as NFPA 70E as an example of common industrial safety practices. Practices that do not follow common guidelines for safety may indicate disregard for safety.

A system that meets all of the NFPA standard's recommendations for safe practices will typically satisfy OSHA's requirements; because NFPA updates most of its standards every three years, staying up to date with its recommendations will also show that a facility is paying attention to new developments in safe work practices.

Preventing Arc Flash in Your Facility
Where electrical hazards exist in your facility, it's important to train the affected workers to understand those hazards and follow safe practices. Employees who aren't performing work on a given piece of powerful equipment should know about the equipment's "danger zones" and how far back to stay. Finally, when work must be performed on energized equipment, your qualified workers need to have the resources to stay safe. That includes detailed equipment labels to keep them informed of details such as what personal protective equipment (PPE) they need to wear.

Brian McFadden works for Graphic Products, a company that provides solutions for safety and visual communications. If you are ready to build a LO/TO system for your workplace or want to learn more about how to apply this kind of system for safety, request a free guide to Lockout/Tagout Best Practices.

Posted on Sep 06, 2016

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