Fire Control Systems in Civil Aviation
There are 4 types of Fire Control Systems on commercial aircraft: (1) lavatory bottle
extinguishing system, (2) on board portable extinguishers, (3) cargo compartment
systems and (4) engine fire protection systems.
All lavatory bottle systems, cargo
compartment systems and engine fire protection systems being installed today use
halon 1301. All on board portable extinguishers being sold today use halon 1211.
The popular belief is that the likelihood of seeing a halon free new commercial aircraft in
the next five or perhaps even ten years is remote. The industry (1) knows it has enough
halon 1301 to last for many years, (2) believes that there are no regulatory bodies ready
to force the issue on this chronically financially ailing industry and (3) knows very well
that all the systems employing alternatives to halons – with the exception of the lavatory
bottle – will cost more, weigh more and take up more space on the aircraft.
Lavatory Bottle Systems
It now appears that several new lavatory bottle fire control systems employing non
ozone depleting agents will be introduced soon. Three agents have successfully passed
the FAA testing: HFC-227ea, HFC-236fa and the Envirogel product (gelled halocarbon
and dry chemical suspension using HFC-236fa). It is nearly a certainty that these new
products will be successfully introduced into the commercial fleet without a lot of
resistance as ……
- they are more effective than the halon 1301 units, …..
- they cost less, …..
- they are the same size as the halon 1301 units, …..
- they mount on the same place in the aircraft, …..
- other than document changes, there’s no engineering required to introduce these
to the fleet.
Cargo Compartment Fire Control Systems
Industry experts feel that the cargo compartment fire protection problem is going to be
the most difficult to solve without the use of halon 1301. The International Aircraft
System Fire Protection Working Group (IASFPWG) considered six extinguishing agent alternatives and concluded that two should go forward for FAA testing: (1) a combination
water mist / inert gas system and (2) a system employing HFC-125.
The FAA has developed minimum performance standards 34 (MPS) for the fire
extinguishing systems for the aircraft cargo compartments and is in the process of
testing agents for this application. FAA testing has demonstrated that water mist by
itself is unable to pass the exploding aerosol can fire test and testing of the two systems
recommended by the IASFPWG has resulted in more interest in the water mist / inert
gas system than one using HFC-125.
However, the economic feasibility of the water
mist / inert gas system depends to some degree on the ability to use an On-Board Inert
Gas Generating System (OBIGGS) for the nitrogen supply, which too is not a reality.
There is also discussion of adding pyrotechnic aerosols to the Fire Control System testing program.
Aircraft Engine Fire Protection
The FAA’s aircraft engine fire protection testing program is similar to the cargo
compartment program in that the IASFPWG considered six extinguishing agent
alternatives and concluded that two should go forward for FAA testing: (1)
iodotrifluoromethane (FIC-13I) and (2) a system employing HFC-125.
While both of these fire control systems have been tested exhaustively by the US Air Force on
aircraft engines, the FAA chose to conduct its own engine testing. Indeed, the Air Force,
Marine Corps and Navy all have operational aircraft flying with HFC-125 systems
protecting their engines. It seems that the FAA has had some instrumentation and other
test setup problems that have plagued their testing efforts with a long series of delays.
Generally, while this program appears to be open ended, there is optimism that it will
provide more tangible results than that from the cargo compartment testing. The reason
for the optimism is that no one expects the test results to be different than those found in
the US Air Force program.
Mobile Military Weapons Systems
The military has done a commendable job in seeking out and selecting alternatives to
halons for its mobile military weapons systems. To name a few, by service branch, in
alphabetical order …..
US Air Force
The Air Force has chosen HFC-125 as the agent for the fire control systems on the F-22
“Raptor” which entered low level production on August 15, 2001.
US Army
The Army has made several advances in employing halon alternatives including …..
- Replacing the halon 1301 systems in the engine compartments with sodium
bicarbonate dry chemical systems on the M1 Abrams Main Battle Tanks as they
are brought in for major overhaul at a rate of approximately 200 vehicles per
year.
- Replaced the halon 1301 systems for the engine compartment protection on the
M2/M3 Bradley Fighting Vehicle with HFC-227ea systems.
- The selection of HFC-125 to protect the engine compartment and the HFC-227ea
/ dry chemical composition system for the crew compartment on the 2,131
Interim Armored Vehicles (IAV) entering production.
- The removal of halon 1301 systems from over 60 Army watercraft and replacing
those with combination HFC-227ea / water-spray fire control systems.
US Marine Corps
The Marine Corps has made these choices for halon alternatives …..
- The employment of HFC-125 as the agent for the extinguishing systems for the
engines and gas generators for the mid-wing bays on the MV-22 “Osprey.”
- The replacement of halon 1301 systems with those using HFC-125 for the engine
protection on the UH1 “Huey” and AH1 “Cobra” fleets.
- The selection of dry chemical fire control system to protect the engine compartment and the HFC-227ea
/ dry chemical composition system for the crew compartment on the
Advanced Amphibious Assault Vehicle (AAAV).
US Navy
The Navy has made these choices instead of continuing the use of halon 1301 …..
The employment of HFC-125 as the agent for the extinguishing systems for the
engines on the F-18 E/F “Super Hornet” and gas generators in the dry bays.
The use of water spray in the main machinery spaces and HFC-227ea in the
auxiliary machinery spaces and flammable liquid storerooms of the LPD-17
Amphibious Transport Dock Ship, a 12 ship lot designated the San Antonio
Class.
The use of HFC-227ea in lieu of the conventional approach of halon 1301
systems for selected machinery protection and flammable liquid storerooms on
the new aircraft carrier USS RONALD REAGAN (CVN 76).
Oil, Gas and Other Process Industries
Process Protection
The use of halon 1301 systems in the oil, gas and other process industries in the US has
been focused in Alaska where, due to the way the facilities were designed and
constructed, the removal of the halon 1301 systems from the process areas is
economically impossible. The process areas in the production modules and the
pumping stations live under continuous threat of methane leaks and potential explosive
atmospheres that are made inert by the existing halon 1301 systems.
For new process areas, involving enclosed modules with a potential methane buildup,
gas detection systems and controls are being used to shutdown and blowdown
processes and to turn on high rate ventilation systems rather than closing up the space and trying to inert it with an extinguishing agent. With the threat of explosion handled in
this manner, the preferred means of protecting against a fire in these new modules is
with a water mist fire control system.
Control Room Protection
Halon 1301 use in the rest of the oil and gas and process industries is somewhat limited
to the protection of electronics in control rooms as the process areas are not enclosed
as they are in Alaska and the gas accumulation problem is not present. Thus the control
rooms in the process industries are not unlike the protection of equipment in the
essential electronics segment. In this regard …..
- Several oil companies are removing their halon 1301 systems from the
electronics areas and (1) replacing those systems with high sensitivity smoke
detection systems or (2) replacing the halon systems with a preaction sprinkler
systems if sprinklers are required by code or (3) replacing the halon 1301
systems with a halocarbon alternative, most often FM-200.
- However, most companies are leaving their halon systems in place in the
electronics areas just as in other industries; perhaps upgrading the detection and
controls and just maintaining the halon protection.
Merchant Shipping
After nearly 25 years of declining shipbuilding of non-military vessels in the US,
construction and orders for new boats and ships of all types are on the rise primarily due
to replacement of aging ships that are part of the Jones Act fleet. While nearly all of the
world’s merchant ships are built in foreign shipyards and registered under flags of
convenience, these foreign flag vessels cannot operate on voyages between two US
ports. The Jones Act requires that cargo moving between US ports be carried in vessels
that are US owned, built and crewed. Similar US cabotage laws reserve the movement
of passengers and the performance of marine services such as dredging, towing and
salvage to US owned, built and crewed vessels.
The new millennium has seen an unprecedented growth of the Jones Act fleet.
Approximately 140 commercial vessels of all types with a market value of more than
$4.4 billion are under construction in American shipyards. Included in that total are the
first large US flag cruise ships in more than 40 years, a number of double-hulled tankers
and tank barges that meet the requirements of The Oil Pollution Act (OPA90), and a new
generation of roll-on/roll-off cargo carriers that incorporate the latest in environmental
safeguards. Pending are contracts for another 150 vessels.
Almost all of this construction has employed total flooding carbon dioxide systems for the
required fire control protection of the engine rooms. It is clearly a cost issue where the merchant
shipping industry makes many of its procurement decisions on two criteria: “Is it USCG
(United States Coast Guard) type approved” and “is it the lowest cost?” The use of
carbon dioxide systems aboard ships is likely to continue indefinitely unless (1) a more
cost effective system is developed and approved (unlikely, when looking at the costs of
the new gaseous alternatives to halons) or (2) something is done to regulate the carbon dioxide systems out of the manned engine rooms.
The US EPA report 37 on the risks of
carbon dioxide systems that enumerated the injuries and deaths attributed to carbon
dioxide fire control systems made special note of the fact that the marine industry had
the most injuries and fatalities of this type.
The majority of the US shipowners have moved seamlessly from halon 1301 back to
carbon dioxide for their mandatory engine room protection for new ships. As such, the
halt of halon 1301 production has not inconvenienced this segment. For the existing
ships with halon 1301 systems installed, these systems will likely continue to serve their
purpose until the ships are scrapped as long as replacement halon 1301 is available to
recharge the systems should they be discharged.
