Arc flash risk assessment: PPE category method (1 of 2) • Electrical Safety 360, June 2017
June 28, 2017 - I am regularly asked by professionals from a variety of electrical sectors to help them nail down comprehensive methods for executing safe electrical work practices in real-world scenarios. This is where the rubber hits the road, involving some of the most important interactions between crews and their management teams.
And yet, it’s not so much about electrical safety specifically but rather electrical safety management within an overall H&S (health & safety) management system.
It is my strong belief that safe work always starts with the implementation of all-inclusive risk assessments, specific to any task in the field.
Having covered the risk assessment procedure (RAP) for shock last time (EBMag March 2017), I now want to share a general overview of the RAP for arc flash against the backdrop of the “Arc flash PPE category method” a.k.a. the “Table method”. (I’ll save incident energy analysis methodology for a future column.)
As always, it is crucial you refer to CSA Z462-15 “Workplace electrical safety”, as it contains specific details, notes and workflow that should be embedded in your business’ electrical-specific, documented procedures.
Z462-15 Clause 184.108.40.206 General states, in part:
An arc flash risk assessment shall be performed. This assessment shall
(a) determine if an arc flash hazard exists. If an arc flash hazard exists, the risk assessment shall determine
(i) appropriate safety-related work practices;
(ii) the arc flash boundary; and
(iii) the PPE that personnel within the arc flash boundary shall use
Determining whether an arc flash hazard even exists is the first priority; if so, the next three steps naturally follow. Arc flash hazards go nearly hand-in-hand with electrical workplaces, but Z462-15 Table 4A, “Arc flash hazard identification for alternating current (ac) and direct current (dc) systems” provides guidance on determining whether an arc flash hazard does, in fact, exist.*
This is a Yes or No question, relying upon the arc flash PPE category method. The information here cannot possibly contain every possible work scenario, but many of the classics are there. When Yes, then steps (i)(ii) and (iii) are required. Let’s look at them in greater detail.
Step (i) can be covered simply by Clause 220.127.116.11 “Documentation”; in this case, “the appropriate safety-related work practices”.
Step (ii), when using the arc flash PPE category method (calculations not being used), goes to Clause 18.104.22.168 for the “Arc flash boundary determination”. This boundary shall be an approach limit at a distance from a prospective arc source within which a person could receive a second-degree burn were an electrical arc flash to occur, and may be determined by Z462 Table 4B or 4C “when the requirements of these tables apply”.
When the requirements of these Tables are not met within the constraints of short-circuit current available and fault clearing times, the arc flash PPE category method cannot be used and an incident energy analysis must be performed.
There’s a very important caveat in Step (iii) when selecting the PPE to be worn by personnel within the arc flash boundary: Clause 22.214.171.124.1 states that only one of the methods described in Clauses 126.96.36.199.2 and 188.8.131.52.3 shall be used for the selection of PPE. Either method, but not both, may be used on the same piece of equipment. The results of an incident energy analysis for specifying an arc flash PPE Category in Table 5 shall be prohibited.
When using the Clause 184.108.40.206.3 arc flash PPE category method, the requirements of Clauses 220.127.116.11.15 and 18.104.22.168.16 shall apply for arc flash PPE selection. Table 5 provides the arc flash PPE requirements for each category under this method. Annex H provides guidance on selecting protective clothing and other PPE.
Clause H.2 covers the use of Tables 4A, 4B, 4C and 5, and is a simplified approach for providing minimum PPE for electrical workers within facilities boasting large and diverse electrical systems. The comprehensive quantifications of arc flash energies can be challenging, and needs to be completed by qualified and competent people. Ensure you are dealing with those truly experienced in getting these values correct. Otherwise, it’s impossible to select PPE appropriate to the circumstances.
* See Clauses 3, 4.3.1, 22.214.171.124.15 and 126.96.36.199.2, Table 5, Annex H.
* This article also appears in the June 2017 edition of Electrical Business Magazine. Check out our ARCHIVE page for back issues.
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