Last year Eclipse Aviation announced that it will use a new fire extinguishing agent called PhostrEx in the Eclipse 500. This new fire suppression system has received approval from the Environmental Protection Agency (EPA) and has passed all FAA certification fire testing. We will take a look at the PhostrEx fire suppression system and discuss how it will affect the aviation industry.
Halon is a term used to describe halogenated hydrocarbons. These materials contain combinations of carbon (C), fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). The halon suffix is based on the number of atoms of each element present in the compound. The numbered suffix for CaFbClcBrdIe would be Halon abcde. However, if there is a zero trailing an element it is dropped. Halon 1301 used in aviation applications is CF3Br.
Halon evolved as a replacement fire extinguishing agent for methyl bromide. Methyl bromide was an effective fire extinguishing agent, but it was toxic. The U.S. Army conducted research in the late 1940s to find a less toxic but still highly effective alternative to methyl bromide. Halons (and specifically Halons 1301 and 1211) were successful in a wide range of fire suppression applications, and became the fire suppressant of choice.
In the 1970s, evidence began to emerge that certain man-made elements were having a detrimental effect on the environment, causing a thinning of the earth’s ozone layer. The environmental impact that Halons and other halocarbons led to the Montreal Protocol (The Montreal Protocol on Substances that Deplete the Ozone Layer) which was an international treaty to place limits on specific forms of pollution. The Montreal Protocol was signed in 1987 and called for a total ban on the production of many halogenated compounds (including Halons) in 1994. Subsequent amendments and implementation of the Montreal Protocol through the U.S. Clean Air Act have led to restrictions on the production and use of ozone-depleting compounds. The 1994 moratorium is in place, and the existing stockpiles of Halon are being conserved for critical uses including military and aviation applications.
Trying to Find a Replacement
Since the ban of Halon 1301, various government agencies including the Departments of Defense, Commerce, and Transportation have conducted research trying to find alternative fire suppressants. These research studies have identified alternatives that ended up being heavier, more costly, more toxic, or in other ways less suitable than Halons. Up until last year, Halon 1301 was the only fire suppression agent that was certified for aircraft fire suppression. All certificated aircraft basically relied upon an exemption from the Clean Air Act and the Montreal Protocol so that it could have a Halon 1301 fire suppression system in their engine compartments to be certified by the FAA. The military also continues to use Halon 1301 for suppression of engine and auxiliary power units, cargo bays, and cabin fires as well as for fuel tank explosion suppression.
Eclipse Aviation Looks for an Alternative Eclipse Aviation began investigating a replacement to Halon 1301 a few years ago as it was proceeding with development of the Eclipse 500. When looking for an alternative, the company asked two basic questions. First, are reactive agents more suitable as agents to suppress fires? And second, could they exploit flow patterns in a fire to use fire extinguishing agents more efficiently, rather than flooding the fire zone with extinguishing materials?
The reason that Halon 1301 is so effective in fire suppression is its chemistry. The primary difference between Halon 14 (CF4) and Halon 1301 (CF3Br) is the presence of a bromine atom in Halon 1301. In a hot fire, the Halon 1301 molecule decomposes and releases the bromine atom in the combustion zone. Bromine catalyzes a recombination of reactive chemical species in the flame shutting off the heat release and extinguishing the fire. But the bromine that makes Halon 1301 so effective also makes it harmful to the ozone layer. Bromine in the stratosphere plays a similar catalytic action, converting ozone to molecular oxygen.
Eclipse Aerospace, Inc. this week received FAA certification and approval for the newly redesigned canister to be used with the PhostrEx fire suppression system on the Eclipse Twin-Engine Jet.
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