Flame Resistant Guide – Hazards
Flash Fire
A flash fire is an unexpected, sudden intense fire caused by ignition of flammable solids (including dusts), liquids, or gases. Flash fires typically last less than 3 seconds and are characterized by extremely high temperatures estimated to range between 550° to 1050°C. The size and duration of a flash fire is generally determined by the amount of fuel available, the efficiency of combustion, and the environmental and physical characteristics of the explosion site.
Flash fires are most common in work areas where flammable materials are handled, processed or stored. In the petrochemical industry, the flash fire hazard exists at well head sites, collection points, compressor stations, refineries, petrochemical and plastic plants.
Flame-resistant clothing is normally used to provide protection against the hazards of a flash fire. Workers not wearing FR clothing that survived flash fires suffered the most severe burns in the areas covered by their regular clothing, which continued to burn and melt long after the flame has receded.
Electric Arc Flash
An electric arc flash is a violent eruption of energy from an electrical source. Arc flashes can reach temperatures of 35,000°F, four times hotter than the surface of the sun, and the resulting explosion of electrical equipment causes an arc-plasma fireball that vaporizes metals, ignites non-FR clothing, and can cause fatal burns at a distance of over 10 ft. In addition to thermal energy, electric arc explosions produce deafening sound waves and pressure waves strong enough to throw a person several feet. Over 2,000 workers are admitted to burn centers each year with severe arc flash burns.
The exposure energy of an electrical arc is expressed in calories/centemeter² (cal/cm²) and the typical arc releases 5-30 cal/cm², although energies of 30-60 cal/cm² are not uncommon. For a point of reference, the hottest point of a lighters flame will generate an energy exposure of between 0.5 and 1 cal/cm². An exposure of 1-2 cal/cm² will cause second degree burns and typical (non-FR) workwear can ignite at 4-5 cal/cm².
Electric arc flashes are most commonly encountered by electric utility workers, electrical maintenance workers and industrial electricians. Although commonly associated with high voltage operations, electric arc flashes are actually more common with lower voltage system typically found in manufacturing facilities. Over 50% of all arc flashes occur at 277 volts.
There are several variables that affect the potential size and force of an electric arc flash. Most significant are the amperage, voltage, arc gap, closure time, distance from arc, 3 phase vs. single phase, and whether the arc occurs in a confined space where the energy level can be two to twelve times greater.
Common electrical equipment capable of generating an electrical arc would include high-voltage switching and grounding gear, panelboards, switchboards, motor control centers, motor starters, metal clad switchgear, transformers, meter bases and meter banks.
