A Flash Fire is defined by the Canadian General Standards Board (CGSB 155.20.2000)* and NFPA (NFPA 2112)* as “a rapidly moving flame front which can be a combustion explosion. Flash fire may occur in an environment where fuel and air become mixed in adequate concentrations to combust; flash fire has a heat flux of approximately 84 kW/m2 for relatively short periods of time, typically less than 3 seconds.”
Flash fires may occur in environments where fuel, typically flammable gas or dust, is mixed with air in concentrations suitable for combustion. In a flash fire, the flame spreads at subsonic velocity, so the overpressure damage is usually negligible and the bulk of the damage comes from the thermal radiation and secondary fires. When inhaled, the heated air resulting from a flash fire can cause serious damage to the tissue of the lungs, possibly leading to death by asphyxiation. Flash fire is a particular danger in enclosed spaces, as even a relatively small fire can consume enough oxygen and produce enough smoke to cause death of the persons present, whether by asphyxiation or by smoke inhalation.
The purpose of FR clothing worn by a worker should be to minimise the severity and percentage of body burn when exposed to a flash fire. Third-degree burn injury should be prevented while second-degree burns should be minimised. This will create the best chance for worker survivability.
Westex Flash Fire Testing Overview
This Westex flash fire testing video was conducted at the University of Alberta’s PCERF Laboratories. PCERF is a protective clothing and equipment research facility and one of the foremost flash fire laboratories in the world. The testing is performed under the protocols of ASTM F1930 and the guidelines of NFPA 2112. The average predicted total area of body burn for the specimens tested must be equal to or less than 40%. Fabrics of differing blends and weights might comply with the standard but they can do so with very different numbers. You can comply at 39% body burn or at 1% body burn, which is an enormous difference. It’s critically important that when you’re evaluating flame resistant fabrics for potential use in your program that you do not consider anything that does not pass the standard.
Understanding Flash Fire Rainwear and ASTM F2733
For the petroleum, petrochemical and chemical industries, the flash fire hazard has been a growing concern. Recently however, several very serious incidents have made the industry look at ways to protect their workforce. The flash fire hazard can be deadly due to the burn injury sustained during an exposure.
A person's ability to survive is a function of their age, the severity and amount of burn injury. Not having the ability to control a workforce's age means an employer must try to reduce the severity and amount of burn injury. As age, severity and amount of burn injury increases, survivability decreases.
This video presented by NASCO Industries, Inc., explains the difference between rainwear that passes a vertical flame test and rainwear that is compliant to ASTM F2733. For workers in the oil and gas industry, this is a must see.
*The CGSB and NFPA standards are similar: however the NFPA 2112 standard is more comprehensive in its requirements. In addition, NFPA 2112 is the first protective clothing standard worldwide to include a requirement that textiles used in FR clothing systems be tested in a simulated flash fire exposure using an instrumented thermal mannequin. This provides a quantitative assessment of the predicted body area burn injury for specified exposure energy using a standard garment made from a specific FR textile.
CGSB - 155.20.2000
Work Wear for Protection Against Hydrocarbon Flash Fire.
CGSB – 155.21.2000
Recommended Practices for the Protection and Use of Work Wear for Protection Against Hydrocarbon Flash Fire.
Standard for Flame Resistant Garments for Protection of Industrial Personnel Against Flash Fire (test protocols ASTM F1930).
Standard on Selection, Care, Use and Maintenance of Flame Resistant Garments for Protection of Industrial Personnel Against Flash Fire.
This standard requires that garments be certified NFPA 2112.
Profile of a Flash Fire
Temperature in excess of 800° C (1470° F).
Heat fluxes up to 4 cal/cm2.
2 to 5 seconds in duration.
- Heat exposure energies up to 20 cal/cm2.
The Hazards of Flash Fires
Severe Burns from Intense Heat and Flame
Unprotected human tissue can be burned by exposure to the heat and flame of a flash fire. Burn injuries are generally very painful and can be life-threatening if a large area of the body is affected.
Severe Burns from Clothing Igniting
Clothing made of flammable fibres can increase the severity of a burn injury. For example, cotton and polyester/cotton blends can ignite and burn under the intense heat of a flash fire, exposing almost the entire body to heat from the burning clothing.
Severe Burns from Synthetic Clothing Melting
Flash fires can generate such intense heat that they can melt garments made from some synthetic materials, such as nylon, polyester and polypropylene. Some synthetic undergarments can melt even when outergarments do not ignite.
Flash Fire - The Relevance of Secondary Protective Clothing
NFPA 2112 test exposure is set at three seconds.
Secondary protective clothing is designed to provide the worker with extra seconds to escape life threatening situations.
CGSB and NFPA define a flash fire as "typically three seconds or less."
NFPA 2112 sets failure above 40% of predicted total area of body burn.