Although Halon 1301 releases bromine into the flame, it does so reluctantly. The bond between carbon and bromine in Halon 1301 is quite strong, and the rate of bromine release is quite slow at typical flame temperatures. It was realized that if a chemical compound could be developed that could release bromine more easily than Halon 1301, it might be more effective in suppressing a fire. This quicker release is possible using a broad class of materials with weakly bound or labile bromine.
A freelance scientist approached Eclipse Aviation around three years ago with a patented material he thought might be of interest to them. Eclipse engineers saw value in his discovery and quickly set up a project to certify the suppressant on the Eclipse 500. The result of that project is PhostrEx — a labile bromine compound chemically referred to as phosphorous tribromide (PBr3). PhostrEx is 87 percent bromine by weight and reacts rapidly with moisture in the air to produce simple, water-soluble acids HBr and H3PO3. This reaction occurs rapidly (0.087 seconds at 50 percent relative humidity). As a result of this quick reaction, the agent cannot be transported to the stratosphere and therefore has no ozone depletion potential. Its byproducts are rapidly deposited by rainfall to the ground and neutralized to simple salts. In a fire, PhostrEx decomposes about one thousand times more rapidly than Halon 1301. It is a very efficient fire suppressant.
One of the advantages of PhostrEx agent is the weight savings. It is much more potent than Halon — two teaspoons of PhostrEx agent are equivalent to 2 ½ cups of Halon. In the Eclipse, the total weight of the PhostrEx fuel suppression system is about 90 percent less than a traditional Halon system would have been.
The PhostrEx fire suppression system is less complex than a Halon system, and is designed to be maintenance free for 10 years. After 10 years, a mechanic simply removes and replaces the hermetically sealed canister. This eliminates typical hydrostatic and visual five-year inspections typically associated with Halon systems.
Eclipse wanted to ensure there would not be any significant health risks with exposure to PhostrEx agent. Since PhostrEx is a reactive agent, it was important to understand any potential toxicity issues. The cartridge is hermetically sealed and is not serviceable. So maintenance personnel don’t handle the chemical itself. Even in the case of accidental discharge of the cartridge, localized concentrations of water-soluble acids are produced that are easily and safely cleaned with water.
Eclipse performed extensive studies on the compatibility of PhostrEx agent to the various materials used in the engine and nacelle area. In addition to the certification tests that were performed, Eclipse is performing compatibility testing on all materials within the engine area including stainless steels, aluminums, wiring harness materials, nacelle composite materials, and the like. All testing so far shows that PhostrEx has no adverse interactions with these materials.
Eclipse is looking ahead to additional installations of the PhostrEx fire suppression system. With all of the environmental issues of Halon, and with a viable alternative now available, there will likely be increased pressure by the EPA for conversion to PhostrEx fire suppression systems. So even if you never work on an Eclipse 500, chances are you will still stumble across a PhostrEx fire suppression system in the future. It’s an emerging technology we will keep an eye on.
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.
H3R Aviation, Inc. is the largest supplier of portable clean agent fire extinguishers to the aviation industry. We offer the general aviation and commercial aviation markets high quality, UL Listed...