Arc flash risk assessment in the workplace: Method 2 of 2 • Electrical Safety 360, October 2017
October 6, 2017 — Having covered risk assessment procedures (RAPs) for shock & arc flash (i.e. PPE category method) in previous editions, the last RAP to cover in CSA Z462-15 “Workplace electrical safety” is the arc flash incident energy analysis method.
The method most commonly relies on IEEE 1584-02 “Guide for performing arc flash hazard calculations”. (An updated edition has been in the works for some time, and is expected in 2018.) Clause 22.214.171.124.2 in CSA Z462-15 references the incident energy analysis method. Of the three RAPs in Z462, this one requires the fewest number of steps.
It is important to note the incident energy exposure level shall be based on the working distance of a worker’s face and chest area from a prospective arc source for the specific task being performed.
Be certain the worker’s hands are also considered in your arc flash RAP, as they are usually far closer to potential arc flash energy than the face and chest area. In fact, try running your IEEE 1584 calculations at the oft-used 18 inches to get your value; now, change the 18-in. value to just 2 in. (for a worker’s hands) and note the massive change in energy.
Without question, voltage-rated gloves—including the protective leathers—are fabulous as both arc flash and shock PPE. As a mandatory best practice, make sure your workers are wearing them on energized or potentially energized equipment.
Once a comprehensive IEEE 1584 calculation has been completed, the incident energy in cal/cm2 and arc flash boundary values will be known. Use Z462 Annex H, Table H.2 (not Clause H.2) to select your arc-rated clothing and other PPE accordingly. There are three levels, as noted in Annex H, Table H.2.
• less than 1.2 cal/cm2
• greater than or equal to 1.2 cal/cm2 (to 12 cal/cm2)
• 12 cal/cm2 or greater
Do not leave out the second step in the risk assessment portion of this procedure. Using IEEE 1584 completes Step #1 of the RAP because it identifies the hazard. Asking risk-based questions—such as those found in CSA Z462 Clause 126.96.36.199.4 “Normal operation”—reveals important information for high-level electrical job planning, such as:
• Has the equipment been properly installed?
• Has the equipment been properly maintained?
• Are all the equipment doors closed and secured?
• Are all the equipment covers in place and secured?
• Is there any evidence of impending failure?
The IEEE 1584 value in cal/cm2 (as per Clause 188.8.131.52.4)—in addition to any of the answers you get to the questions above from your experienced electrical workers, supervisors and managers—lead you to Step #3 of the RAP, which is to document the procedural steps for executing electrical work safely (hierarchy of risk control methods).
I have a few final thoughts you should always consider when using the arc flash incident energy analysis method.
It is critical to have a fully qualified, competent and experienced person performing these calculations. Comprehensive data collection needs to be done in the field, not at a desk. This is, again, a mandatory best practice.
Most importantly, when your IEEE 1584 calculations are done very well but they are not 100% aligned with quality and regular electrical maintenance best practices, you have accomplished very little. Quality maintenance is directly proportional to the timing of the upstream tripping/clearing devices. When your breakers or relays, for example, do not operate as per your design specs and setting sheets, you have likely wasted most of your monetary resources for that project.
For maintenance on overcurrent protective devices, see also Z462 Clause 5.2.4 and Annex B, and CSA Z463-13 “Guideline on maintenance of electrical systems” for best practices and guidance. In fact, CSA Z463 will soon be upgraded from being a Guideline to a Standard.
As noted in my last column, refer to Z462 Clause 184.108.40.206.1, which states that only one of the methods described in Clauses 220.127.116.11.2 and 18.104.22.168.3 shall be used for the selection of PPE. Either method—but not both—may be used on the same piece of equipment.
As always, it is crucial you refer to CSA Z462-15, as it contains specific details, notes and workflow that should be embedded in your business’ electrical-specific, documented procedures.
* This article also appears in the October 2017 edition of Electrical Business Magazine. Check out our ARCHIVE page for back issues.
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