Arc Flash Study From the incident energy analysis

Incident Energy at the Working Distance cal/cm²

From the equipment label or the study, at the working distance of the task. Divide a J/cm² figure by 4.184.

Design Margin Wanted %

Extra cover above the study figure that some programmes write in. Enter 0 to check against the bare figure, which is what the rule requires.

Garment From the label

Arc Rating of the Clothing (ATPV or EBT) cal/cm²

Printed on the garment label, measured on the fabric or the fabric system. For a flash suit or a tested two-layer system use the system rating; never add single-layer ratings.

Face & Head Protection Arc Rating cal/cm²

Arc-rated face shield with balaclava, or the flash suit hood. Enter 0 to leave it out.

Arc Rating over the Required Rating

— x

At 1.0 or more the clothing meets or exceeds the exposure

Check

Clothing Meets or Exceeds the Exposure: — 1 = yes
Arc Rating Required: — cal/cm²
Margin above the Requirement: — cal/cm²
Incident Energy: — J/cm²
Arc Rating: — J/cm²
Exposure Above 1.2 cal/cm²: — 1 = yes
Highest PPE Category the Rating Meets: — category
Short of the Next Category Minimum: — cal/cm²
Face Protection Meets the Exposure: — 1 = yes

Category minimums are those of NFPA 70E Table 130.7(C)(15)(c) (2018 numbering) as reproduced by e-hazard and EC&M: 4, 8, 25 and 40 cal/cm² for PPE Categories 1 to 4; check the edition your programme cites, as later editions renumber the tables. The 1.2 cal/cm² (5 J/cm²) threshold is where incident energy falls to the onset of a second-degree burn and is how the arc flash boundary is defined. Under the incident energy analysis method the arc rating must meet or exceed the estimated incident energy; a design margin is your programme's choice, not the standard's. The arc rating is the ATPV, the incident energy at which there is a 50% probability of a second-degree burn through the fabric, or the EBT where the fabric breaks open first; the label carries whichever applies. The category output reads the garment label only: it does not choose a PPE category from the incident energy, because the category method and the incident energy method are not to be mixed. **A layered system is rated by testing the system; this tool never adds layers.**

Arc-Rated Clothing Check: Incident Energy vs Arc Rating & NFPA 70E Category — free, with the formula and a worked example, at Textile School.