Electrical safety: Shock and Arc Flash boundaries
Shock and Arc Flash boundaries
After an Incident Energy analysis, the team of experts that carried out the analysis installed warning labels on all of the equipment with the corresponding incident energy levels as well as the many boundary values. In this blog, all the normative information found on the warning labels will be broken down and you will learn to understand all their different values.
Here is an image describing the different Shock and Arc Flash boundaries. The working distance must also be taken into account when choosing PPE against Arc Flash.
Figure 1: Arc Flash and Shock boundaries
Description of the different boundaries
The Arc Flash boundary is the distance at which an unqualified worker can expose himself while minimizing the damages possible without Arc Flash PPE. However, if the Incident Energy level is low, this limit may be lesser and PPE against shock may be required. The Arc Flash boundary is determined for the onset of a second-degree burn or an Incident Energy level of 1.2 cal/cm2. That is to say that the temperature of the skin does not reach 80°C (176°F).
The working distance is determined from incident energy level calculations at 455mm (18’’) from all points of a conductor or other bare live circuit elements. This distance lies between the worker’s face and torso and the potential arc source. The worker must be qualified and must be wearing PPE that is appropriate to the incident energy level. It is also possible to determine the PPE category from tables 6A and 6B from the CSA Z462-18 standard.
The Limited approach boundary is the distance at which a qualified worker or an unqualified worker continuously escorted by a qualified worker can circulate without using PPE against shock. However, according to the incident energy level, it is likely the worker may have to wear Arc Flash PPE.
The Restricted approach boundary is the distance between the source and the worker under which he or she must wear PPE against electric shock. At this distance, it is possible that the worker will also have to wear Arc Flash PPE.
The Arc Flash boundary is the most constraining distance between the Arc Flash boundary and the Limited approach boundary.
Explanation of labels
Warning labels must take into account Arc flash and Shock Hazards. For Shock Hazards, the distance is directly influenced by the voltage. Therefore, for all the 600 V equipment in a plant, the Limited and Restricted approach boundaries will be respectively set as 1 m (3 ft 6 in) and 0.3 m (1 ft) for bare stationary circuit elements. Furthermore, for arc flash protection, the incident energy is evaluated at a 455 mm (18 in) distance and will inform of the PPE to be worn. For an incident energy of 8 cal/cm2, the qualified worker must wear PPE equal or superior to this value.
Figure2: Warning Label
This blog provided the opportunity to learn more about the information found on Arc Flash and Shock Hazard labels and how they are created. To learn more, please see our blogs on arc flash PPE, Electrical safety: What to do in case of electrical shockand Electrical safety: Incident energy study.
- IEEE 1584-2002 – IEEE Guide for Performing Arc Flash Hazard Calculations
- CSA Z462-2018 – Workplace Electrical Safety
- CSA Z462-2015 – Workplace Electrical Safety
- CSA Z463-13 Guideline on maintenance of electrical systems
Questions or comments?
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Intervention Prévention concentrates its operations in the field of work safety, offering specialized services following Standards CSA Z462 – Workplace Electrical Safety, CSA Z460 – Control of Hazardous Energy: Lock-out and Other Methods, and CSA Z432 – Safeguarding of Machinery.
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