An electrical arc at 13.8 kV releases plasma at 19,000 °C and pressure waves that can collapse lungs. IEEE 1584 calculates incident energy in cal/cm². NFPA 70E maps that to PPE category. Saudi sites that skip the calc kill people.
Four ideas to carry into the next specification conversation you have.
The thermal energy reaching a worker's skin during an arc fault. 1.2 cal/cm² = onset of second-degree burn at 30 cm distance.
Category 0 = no special PPE (≤ 1.2 cal/cm²). Category 4 = 40+ cal/cm² arc suit. Above Category 4, work is forbidden energised.
Three concentric zones around the panel. Flash protection boundary = where second-degree burn risk ends. Inside it, full PPE.
Arc flash labels per IEEE 1584 mandatory on every switchgear panel: incident energy at working distance, boundary distance, PPE category.
Per NFPA 70E Table 130.7(C)(15)(c). Saudi sites adopt the same scale.
| Category | Min arc rating | PPE required |
|---|---|---|
| Category 0 | ≤ 1.2 cal/cm² | Non-melting long-sleeve + safety glasses |
| Category 1 | 4 cal/cm² | Arc-rated FR shirt + pants OR coveralls |
| Category 2 | 8 cal/cm² | FR shirt + pants + face shield + balaclava |
| Category 3 | 25 cal/cm² | Arc flash suit hood + jacket + bib overall |
| Category 4 | 40 cal/cm² | Full arc flash suit + hood + gloves |
| > 40 cal/cm² | Not allowed energised | De-energise first, no PPE rated |
Five steps that turn an IEEE 1584 calc into a safety system.
Arc flash energy at any point depends on the upstream fault current and protection clearing time. ETAP, EasyPower, SKM PowerTools model the entire installation. A single calc on one panel without upstream coordination is useless.
Incident energy is roughly proportional to fault current × clearing time. A breaker clearing in 0.05 s gives 10× less energy than one clearing in 0.5 s. Faster protection at every level is the cheapest way to drop PPE categories.
The previous 2002 method underestimated energy at 240 V. The 2018 update added box geometry, electrode orientation, and arc-current variation. Saudi consultants still using 2002 are running outdated risk numbers.
NFPA 70E + Saudi OSHA / SBC require an arc flash label on every panel rated > 50 V where work might be done energised. Label includes incident energy at working distance, flash boundary, and PPE category. Re-issue after any system change.
Some breakers have a 'maintenance mode' (e.g. ABB Emax MMS, Schneider Energy Reduction Maintenance Setting) that drops trip delays to minimum during planned work, temporarily reducing arc energy by 60-80%. Spec these on critical sites.
We deliver IEEE 1584-2018 arc-flash studies (ETAP), apply NFPA 70E labels to every panel, and spec breakers with Energy Reduction Maintenance Setting for safer maintenance windows.
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