An arc flash study is a detailed engineering assessment, typically performed by a qualified electrical engineer.
Using methodologies such as IEEE 1584, the study evaluates:
- System fault levels
- Protection device settings
- Equipment configuration
- Working distances
The output is a calculated incident energy (cal/cm²) at specific points in the system.
This information is then used to:
- Assign PPE requirements
- Define arc flash boundaries
- Generate equipment labels
Step-by-Step: How to Determine Arc Flash Category
- Identify the equipment and task
- Use an arc flash study or approved table
- Determine incident energy (cal/cm²)
- Compare against PPE thresholds
- Assign category (if used)
- Select PPE rated ≥ required energy
Therefore, PPE must match the energy level, not just the category minimum ATPV.
Arc Flash Study vs PPE Tables
There are two common methods used to determine arc flash category — a detailed arc flash study or simplified PPE tables. Therefore, understanding the difference is critical, as each approach offers a different level of accuracy.
Arc Flash Study
- Site-specific and accurate
- Based on IEEE 1584
- Best practice and preferred approach
PPE Tables
- Simplified guidance from AS/NZS 4836 and/or NFPA 70E
- Only valid if conditions match exactly
- Guide only
However, while tables are useful, they should not replace proper assessment.
Understanding Arc Ratings (ATPV and EBT)
Arc flash category helps guide PPE selection; however, the actual level of protection comes from the garment’s arc rating.
Arc-rated PPE is measured in cal/cm² using:
ATPV (Arc Thermal Performance Value)
- Measured in cal/cm²
- Most commonly used rating in Australia & New Zealand
- Energy level where there is a 50% probability of a second-degree burn through the fabric
ELIM (Incident Energy Limit)
- Measured in cal/cm²
- Alternative rating used in European standards, calculated similarly to ATPV but representing a lower probability of injury
- Energy level at which there is a 0% probability of a second-degree burn
APC Box Test (Arc Protection Class Test)
- Measured in Class 1 or Class 2
- Most commonly used rating in Europe
- Classification of PPE performance under a simulated arc in an enclosure, used to determine a pass/fail performance
Therefore, these values indicate how much energy a garment can withstand before causing injury.
As a result, PPE must be rated to meet or exceed the incident energy.
How to Read an Arc Flash Garment Label
Arc flash labels typically show:
- Incident energy (cal/cm²)
- Working distance
- Required PPE or category
Importantly, the key value is incident energy.
For example:
40 cal/cm² → PPE must exceed this → typically Category 4.
Why Incident Energy Matters More Than Category
Arc flash category is a simplified system. However, the real measure of risk is incident energy.
Industry guidance, including Energy Networks Australia, reinforces that PPE selection should be based on calculated energy levels wherever possible.
Therefore, category helps guide decisions — energy defines them.
Australian Standards and Legal Expectations
Arc flash is a recognised hazard under Australian safety frameworks.
Key standards include:
- AS/NZS 4836
- AS 2067
- IEC 61482
Supported by:
- NFPA 70E
- IEEE 1584
Australian regulators, including WorkSafe Queensland, are clear:
De-energise equipment wherever possible.
Where live work is required:
- Risks must be assessed
- Controls must be applied
- PPE must be correctly selected
Ultimately, arc flash is a known and controllable hazard.
Common Mistakes
- Guessing the category
- Using outdated studies
- Ignoring working distance
- Wearing non-rated PPE
- Assuming 100% cotton garments are FR (Fire Retardant Rated)
As a result, these can lead to inadequate protection.
What Should You Do on Site?
- Check arc flash labels
- Follow the site study
- Confirm conditions match
- Select PPE based on incident energy
Ultimately, never assume.