Ultimate Deadline for Halon Replacement Strains Credulity

Tue, Aug 3, 2010 — David Evans

Articles, Featured

The notion of allowing airlines 30 years to install improved fire fighting technology is ludicrous. That generous grace period is proposed by the European Union while various alternatives to the present environmentally hazardous fire fighting chemical are already available. A five-year grace period seems more than enough to handle the transition.

As in the Continental overrun at Denver in 2008, fire remains a principal danger and substitutes for Halon are available.

As in the Continental overrun at Denver in 2008, fire remains a principal danger and substitutes for Halon are available.

The European Commission is circulating a draft regulation of May 2010 that bears citation as an example of setting requirements so far into the future they do not disturb the present status quo.



“Amending Regulation (EC) No. 1005/2009 of the European Parliament … on substances that deplete the ozone layer, with regard to the critical use of halons …


“(1) Halon 1301, halon 1211 and halon 2402 (hereinafter referred to as ‘halons’) are ozone-depleting substances listed as controlled substances in Grout III of Annex I to Regulation (EC) No. 1005/2009. Their production in Member States has been banned since 1994, in line with the requirements of the Montreal Protocol. Their use, however, continues to be permitted for certain critical uses as set out in Annex VI to Regulation (EC) No. 1005/2009 …

‘(5) The review has also shown that halons are being replaced or could be replaced by alternatives over time and at a reasonable cost for a majority of fire protection n applications …

“(13) For fire protection systems in [aircraft] cargo compartments, engine nacelles and auxiliary power units, on existing civil aircraft or on those being produced in accordance with an existing type certificates, alternatives have … not yet been identified … [It] is appropriate … to identify and develop suitable alternatives, to set 2040 as a reasonable end date.”

That’s where the 30-year grace period comes from: 2040 – 2010 = 30 years.

Remember, halons have been banned from production since 1994, and airlines are operating under an exemption that allows the use of halons until an equal or better alternative has been developed. So the total grace period is 2040 – 1994 = 46 years.

In other words, the airline industry is going to operate under nearly a 50-year exemption. One would think, with the wholesale ban of propellants in spray cans of deodorant, hairspray, and other products because of the awful effects on the atmosphere, that a more aggressive effort regarding halon as an aircraft fire fighting agent would be warranted.

Halon as been described as “God’s gift to fire fighters” due to its impressive extinguishing effects and its relatively long storage in pressurized canisters, not to mention its benign effects on people.

According to a 2002 progress report from the FAA on options to the use of halons (Report No. DOT/FAA/AR-99/63), a family of so-called “halocarbons” might be considered, but there are problems:

“All of the halocarbon agents have trade-offs … As noted earlier, halon replacements should have four characteristics: a low global environmental impact, acceptable toxicity, cleanliness/volatility, and effectiveness. Though it is very easy to find candidate replacements that meet any three of these criteria, it has been difficult to find agents that meet all four. For most (but not all) applications, significantly more replacement agent is needed to provide the same degree of protection as provided by the present halons …

“One potential problem that occurs with many (but not all) of the new halocarbon agents is that they generate four to ten times more hydrogen fluoride (HF) than Halon 1301 does during comparable extinguishment …

“At concentrations of <50 ppm for up to 10 minutes, definite irritation of upper respiratory tract, skin, and eyes would be expected to occur. At these low concentrations, escape-impairing effects would not be expected in the healthy individual. As HF concentrations increase to 50-100 ppm, an increase in irritation is expected. At 100 ppm for 5 minutes, moderate irritation of all tissue surfaces would be expected, and as the duration of exposure increases to 10 minutes, escape-impairing effects would begin to occur. As the concentration of HF increases, the severity of irritation, including escape-impairing irritation of the eyes and respiratory tract, increases … At these higher concentrations, humans would be expected to shift to mouth breathing, and deeper lung irritation is expected. At greater concentrations (>200 ppm) respiratory discomfort, pulmonary (deep lung) irritation, and systemic effects are possible. Continued exposure at these concentrations may be lethal in the absence of medical treatment.”

Pretty grim. The fire is extinguished, but choking or dead passengers are the side effect. The FAA report details alternatives to halocarbons:

— Water misting.

— Particulate aerosols.

— Inert gases.

— Solid propellant gas generators.

— Some combination of the above.

Water misting may be particularly suitable for main deck and cargo hold fire extinguishing. According to the report:

“Water misting systems allow the use of fine water sprays to provide fire protection with reduced water requirements and reduced secondary damage. Calculations indicated that on a weight basis, water could provide fire extinguisher capabilities better than those of halons provided that complete or near-complete evaporation of water is achieved. Since small droplets evaporate significantly faster than large droplets, the small droplets achievable through misting systems could approach this capability. The NFPA [National Fire Protection Association] 750 Standard on water misting systems establishes 1,000 microns ?(micrometer, µm) or less as being the water droplet size for a system to be designated as a water misting system; however, many existing systems have droplet sizes well below this value. Water misting systems extinguish fires by three mechanisms: (1) heat absorption through evaporation and, to a lesser extent, vapor-phase heat capacity, (2) oxygen dilution by the water vapor formed on evaporation, and (3) radiative heat obstruction by the mist …

“The use of water mists for protection of [engine] nacelles may be difficult. First, the low temperatures, around -57ºC (-70ºF) at altitudes of 36,000 feet, hinder storage, discharge, and evaporation. Second, there is concern about the possible collateral damage due to thermal shock when water contacts hot titanium components.”

Advanced Firefighting Technology claims its system delivers droplets of 150 micron size that outperform comparable products.

Advanced Firefighting Technology claims its system delivers droplets of 150 micron size that outperform comparable products.

A water mist system can utilize low-pressure plastic tubing and the airplane’s on-board potable water supply (thus minimizing the weight requirement). The industry has been reluctant to install water mist systems because of their perceived negative impact on sensitive avionics, although tests have shown this apprehension is unfounded.

Suffice to say, the industry has a lengthy list of alternatives, and there is a seemingly endless list of disadvantages that make any alternative to halons seem second rate. But some aircraft manufacturers have developed and installed alternatives. Case in point: the PhostrEx fire suppression system installed on the Eclipse 500 business jet. In a 2005 white paper on the system, Eclipse hails PhostrEx as “the world’s first commercially viable Halon replacement.”

Since PhostrEx was certified by the FAA, the alternative to halons may be at hand. Here is what the white paper proclaims:

“PhostrEx is 87% by weight bromine and reacts rapidly with moisture in the atmosphere to produce simple, water soluble acids HBr and H3PO3. As a result of this reaction, which occurs on 0.087 seconds at 50% relative humidity, the agent cannot be transported to the stratosphere and therefore has ZERO ozone depletion potential and contributes nothing to global warming. Its byproducts are rapidly deposited by rainfall and neutralized to simple salts on the ground.

“In a fire, this material decomposes about one thousand times more rapidly than Halon 1301 … The essential point is that efficient delivery of bromine atoms or hydrogen bromide gas into the combustion zone quenches a fire using tiny quantities of suppressant …

“As an added benefit, we have found that ambient flows within the nacelle can be used to transport agent to flame holding regions more effectively and with less engineering complexity (and no plumbing weight) than is commonly used for total flooding Halon systems.”

The PhostrEx suppression system's flame poisoning chemistry.

The PhostrEx suppression system's flame poisoning chemistry.

It’s pretty clear from a search of the Internet that water mist systems are already on the market for aviation applications, as is PhostrEx. The point is not to extol these particular technologies, but to point out that 16 years after halon production ceased, substitutes have been developed and are available for airline use.

The 2040 deadline just delays installation and encourages foot dragging. Getting the job done by 2015 seems do-able, certainly for all new-production airliners. A deadline of 2020 for retrofitting existing airliners seems reasonable – although older airplanes have worse fires from contaminated insulation blankets, chemical spills, flammable dirt, grease and whatnot. A deadline for both new and exiting airliners of 2015 would maximize the safety of the flying public 25 years sooner than envisioned by the European Commission.

Ask if 2040 is a reasonable deadline, and the answer is apparent: they can’t be serious!

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