In an instant, a flash fire can cause serious harm to people and catastrophic damage to property. There is no time to react. To get through it safely, all the controls and protection have to be in place well before the fire occurs.
What Is a Flash Fire?
The National Fire Protection Association (NFPA) defines flash fire as “A type of short-duration fire that spreads by means of a flame front rapidly through a diffuse fuel, such as dust, gas, or the vapors of an ignitable liquid, without the production of damaging pressure.” (That last detail distinguishes a flash fire from an explosion, which has other injury-causing characteristics due to pressure.)
Preventing Flash Fires
Flash fire protection strategy is focused on heat energy, and accounts for the fact that a flash fire incident will run its course in milliseconds. Jumping out of the way of a fireball is just for the movies! You need a lot more planning in real life.
(Learn about 4 Solutions to Eliminate Arc Flash Hazards in the Workplace.)
Fire requires three basic components: oxygen, fuel, and an ignition source. Together, they're known as the "Fire Triangle."
When the oxygen source is ordinary air, there is a known stoichiometric ratio of flammable substances and air that will burn. If the mixture is too lean (not enough fuel) or too rich (too much fuel), you won’t get ignition. The principal means of preventing flash fire burns is to prevent workers from entering atmospheres where the air-fuel ratio is in the flammable range.
Employers can use air monitoring procedures to make sure the lower explosive limit (LEL) (the lowest concentration of fuel vapor in air that will burn) is not approached. Generally, 10% of the LEL is considered an alarm conditions and workers will vacate or simply not enter that area until it can be ventilated or inerted.
(Learn more in Gas Monitoring Reduces Worksite Accidents.)
PPE Protection for Flash Fires
Even with engineering and administrative controls in place, some risk of flash fire might remain. In this case, PPE provides a last line of defense. It can't prevent fires from happening, but it can reduce the severity of the injuries caused by them.
NFPA Code 2112 lays out the criteria for testing and certifying garments as suitable for flash fire protection. It uses a number of associated standard testing methods to come up with a basic pass/fail grade for the clothing. Garments that pass can bear a tag that reads “This clothing item meets the requirements of NFPA 2112-2018. NFPA 2113 requires upper and lower body coverage."
Here's what PPE has to go through to earn that label.
ASTM’s F2700 testing method evaluates textile performance against the kind of heat transfer you would see in a flash fire. All fabrics used in flame resistant apparel need to have a minimum “Heat Transfer Performance” (HTP) rating of over 6.0 cal/cm2 and a “contact” HTP rating of not less than 3.0 cal/cm2. Heat transfer performance is determined by exposing the material to a 2 cal/second flame, while a sensor on the other side records how much heat passes through the materials. The test is terminated when enough heat has passed through to cause a second-degree burn.
Flame resistance is tested using the ASTM vertical flame test as specified in the standard D6413. This is a common approach for most fire resistant garments. Basically, it involves applying a flame to the material, then recording the afterflame time (the time a material continues to burn following a flame exposure) and the char length (the burnt area where the flame was applied). The test assesses how much of the material is consumed by the flame, but also looks out for failure criteria like dripping.
All garments also have to be subjected to the so-called manikin test (ASTM F1930) in order to assess the full garment, including seams, clasps, hardware, and layered areas. The manikin contains instruments that help estimate the severity of the body burns a worker would suffer following a 3 second, 2 cal/cm2 simulated engulfment flash fire. The predicted total body burn of second-degree or worse burns (excluding hands and feet) must not exceed 50%. The test is quite technical, involving an intimidating half-page heat flux calculation, as well as specification all the way down to what kind of underwear the manikin has to be wearing.
Make Sure Your Protective Clothing Is Up to Snuff
Every effort must be made to avoid a flash fire incident, you'll need to rely on protective clothing and other PPE to reduce the severity of the burn. PPE is the last line of defense and a lot of scientific rigor and diligent standardization goes into making sure that it's an effective one.
If your workers could be exposed to flash fires, make sure they're equipped with protective gear that meets the exacting standards of the NFPA Code 2112.
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