Arc Flash Hazard Analysis: What Every Building Owner Needs to Know Before It's Too Late
An arc flash can reach 35,000°F — four times the surface of the sun. It can kill a worker in milliseconds and destroy equipment worth hundreds of thousands of dollars. Ontario law requires employers to identify and mitigate this hazard. Here's what you need to know — and what you need to do.
What is an Arc Flash?
An arc flash is a sudden, explosive release of electrical energy through the air when current jumps between two conductors or from a conductor to ground. Unlike a shock (which requires physical contact), an arc flash creates an arc plasma fireball that can:
- Generate temperatures up to 35,000°F (19,400°C)
- Create a pressure blast wave of 2,000+ lbs/ft² — enough to throw a worker across a room
- Produce shrapnel from vaporized copper conductors expanding to 67,000 times their original volume
- Emit intense UV and IR radiation causing severe burns at distances of 10+ feet
Is an Arc Flash Study Legally Required?
In Ontario, the answer is effectively yes. While the Occupational Health and Safety Act (OHSA) doesn't use the phrase "arc flash study," it requires employers to:
OHSA Section 25(2)(h): Employers must "take every precaution reasonable in the circumstances for the protection of a worker."
CSA Z462 (Workplace Electrical Safety) is the recognized standard for compliance. It requires an arc flash risk assessment for any electrical equipment that may be serviced while energized.
If a worker is injured by an arc flash and no study was performed, the building owner and employer face criminal liability under the Westray Bill (C-45) and OHSA penalties up to $1.5 million per offence.
IEEE 1584: How Incident Energy is Calculated
The industry standard for arc flash calculations is IEEE 1584-2018. The calculation determines the incident energy (in cal/cm²) at a given working distance from the arc source. This energy level dictates what PPE a worker must wear.
Key inputs to the calculation:
| Input Parameter | What It Means | Where to Get It |
|---|---|---|
| Available fault current (kA) | Maximum short-circuit current at the equipment | Utility data + short circuit study |
| Clearing time (cycles) | How fast the upstream breaker trips | Breaker TCC curves + coordination study |
| Working distance (mm) | Distance from the worker's face/chest to the arc | IEEE 1584 Table (typically 455–910mm) |
| Electrode configuration | Open air, box, or barrier | Equipment type (panel, switchgear, MCC) |
| System voltage (V) | Nominal voltage at the equipment | One-line diagram |
| Gap between conductors (mm) | Physical spacing inside the equipment | Equipment drawings or field measurement |
PPE Categories and Incident Energy Levels
| PPE Category | Incident Energy Range | Required PPE | Typical Equipment |
|---|---|---|---|
| 1 | 1.2 – 4 cal/cm² | Arc-rated shirt/pants, safety glasses, hard hat | 120V panels, small control panels |
| 2 | 4 – 8 cal/cm² | Arc-rated coveralls, face shield, balaclava | 208/240V panelboards, small MCCs |
| 3 | 8 – 25 cal/cm² | Arc flash suit (hood, jacket, pants), leather gloves | 480V switchboards, large MCCs |
| 4 | 25 – 40 cal/cm² | Multi-layer arc flash suit, full hood, heavy gloves | Medium voltage switchgear, large 600V gear |
| Dangerous | > 40 cal/cm² | NO PPE is sufficient — work MUST be de-energized | Main switchgear with slow clearing times |
The goal of an arc flash study is NOT just to specify PPE — it's to engineer the hazard down. By upgrading breakers, adjusting trip settings, or adding zone-selective interlocking, incident energy can often be reduced by 50–80%, moving equipment from Category 4 to Category 2 or even Category 1.
Arc Flash Boundaries
The study also calculates three critical safety boundaries around each piece of equipment:
- Arc Flash Boundary: The distance where incident energy falls to 1.2 cal/cm² — the onset of second-degree burns. Workers inside this boundary must wear rated PPE
- Limited Approach Boundary: Only qualified persons may cross this line
- Restricted Approach Boundary: Shock hazard — requires specific training and PPE for shock protection
What a Complete Arc Flash Study Delivers
- Short circuit study: Available fault current at every bus and panel in the facility
- Coordination study: Verification that breakers trip in the correct sequence
- Incident energy calculations: cal/cm² at every piece of switchgear, panelboard, and MCC
- Arc flash labels: ANSI-compliant warning labels for every panel (orange/white format)
- Mitigation recommendations: Breaker upgrades, settings changes, and design modifications to reduce hazard levels
- PPE requirements table: Exactly what each worker needs to wear at each location
Common Misconceptions
- "We only work on de-energized equipment" — even verifying that equipment IS de-energized exposes workers to arc flash risk. Testing for absence of voltage is an energized task
- "Our building is too small for arc flash" — even a 200A, 208V residential panel can produce dangerous arc flash. Size doesn't determine risk; available fault current does
- "We did a study 10 years ago" — CSA Z462 recommends updating arc flash studies every 5 years or whenever the electrical system changes
- "PPE is enough" — PPE is the last line of defense. A proper study focuses on engineering controls to reduce incident energy, not just specifying thicker suits
Download the Arc Flash Study Checklist
Get our pre-study data collection checklist — everything your team needs to gather before the engineering assessment begins.
Need an Arc Flash Study?
ETEM Engineering performs IEEE 1584-compliant arc flash hazard analyses, short circuit studies, and protective device coordination for commercial and industrial facilities across Ontario. We deliver the full package — calculations, labels, and mitigation recommendations.
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