Personal Protective Equipment (PPE) » Factors Affecting Heat Exposure

For work that may produce electric arcs, employers and workers need to know what factors can affect workers' exposure to heat from the arc. These factors can be particularly important when high exposures need to be reduced, or when conditions that can create new hazards need to be avoided.

One such condition that is often overlooked when selecting PPE and FR clothing is cold, in addition to the more frequently encountered condition of heat stress. The effects of these environmental stressors are greatly impacted by the FR clothing that may be required for differing levels of exposure in different climates. For additional information on this topic, see OSHA's Safety and Health topics page on Heat Stress.

The four major factors that affect how much heat a worker receives from an arc are:

  • Fault current
  • Arc length
  • Arc duration
  • Distance the worker is from the arc

If any one of the first three factors – fault current, arc length, or arc duration – changes by a certain amount in a certain direction (increases or decreases), a worker's heat exposure will change by approximately the same ratio or percentage in the same direction (increase or decrease). For example, if the arc duration is reduced by one-half, the amount of heat exposure is also reduced by approximately one-half:

arc duration (or fault current or arc length) ÷ 2 ≈ heat exposure ÷ 2

The relationship between the fourth factor – distance from an arc – and heat exposure is different than the first three factors. Heat exposure changes inversely (in the opposite direction) with the approximate square of the distance. This inverse relationship between heat exposure and distance can be expressed as:

Heat exposure ≈



For example, doubling a person's distance from a potential arc, by using a longer live-line tool, would result in a worker receiving approximately one-quarter of the original heat exposure; tripling the distance would result in approximately a nine-fold decrease in heat exposure, etc. Use longer live-line tools and distance yourself from the hazard.

Flame-Resistant (FR) Clothing
Best Practices for Arc Exposures and Use of FR Clothing
Insulating Protective Equipment (IPE)