Two Minutes To Live
FEATURES
RESCUE TECHNIQUES
Air travel has become an increasingly common means of transportation in today’s modern world. While it is considered to be relatively safe, accidents do occur.
After the skill of the pilot, the effectiveness of the aircraft’s technology, and the best navigational aids have failed, the survival of the passengers on the aircraft is left to the ability of the air crash firefighting and rescue operation.
Here is a loose definition of the term rescue: “Rescue begins when the first arriving CFR (crash fire rescue) vehicle reaches the scene of the incident/accident and begins to effectively apply extinguishing agent.” However, to an occupant who is immobilized inside the aircraft, rescue means “the ability of the first arriving CFR vehicle with sufficient extinguishing agent to control the fire and manpower to remove those people trapped inside the aircraft.”
Let’s look at the first definition of rescue, which means that there are sufficient extinguishing agents being applied in the practical critical area* to allow passengers egress by themselves. This is an acceptable interpretation, but the traveling public must be aware that this is the case. However, if a passenger is not physically capable of moving on his own, he will have to wait until the rescue personnel are organized and on the accident scene.
So for this article, we will adopt the loose definition of rescue and agree that the rescue begins with
the effective application of the extinguishing agent(s) on the fire.
The scene is an in-flight interior cabin fire. The pilot safely lands the aircraft on the runway, the exit doors are opened, fresh oxygen rushes into the aircraft passenger cabin, and the fire quickly intensifies, accelerating the production of thick, black, toxic smoke.
The field of vision inside the fusilage becomes totally obscure, the passenger’s breathing becomes impaired, his eyes are running water, and he cannot see the end of his nose. He becomes totally disoriented.
But, in the background of all the noise and confusion he recognizes the sound of the aircraft firefighting and rescue vehicle siren.
Help is now only seconds away.
He can hear something splashing against the fusilage of the aircraft. He tries to remain conscious, but the situation inside the plane is not improving. Finally, he succumbs to the toxic fumes. His last thoughts are focused on the hope that he will survive, but he does not.
Interior cabin fires must be fought with the same tactics that are used to combat a structure fire. Firefighters must man hose lines and enter the cabin’s interior through available access points. Their goal is to reduce the temperature of the combustible material below the ignition temperature. Because there are still people on board the aircraft, the firefighters must use reduced water stream pressure.
Rescue personnel can easily fight these fires by using a medium expansion foam nozzle. This nozzle can cover interior seats and luggage very quickly and is more effective in extinguishing fires than aqueous film forming foam (AFFF), fluoroprotein, or plain water discharging from the standard firefighting foam nozzle.
EXTINGUISHMENT
Let’s now look at aircraft firefighting in greater depth to make sure we have not overlooked other areas.
Non-air aspirating versus air aspirating discharge nozzles/monitors
One obvious error in judgement is restricting the type of foam liquid concentrate that can be used with this type of hardware. Air aspirating nozzles can be used to apply foam made from any type of foam liquid concentrate, but non-air aspirating nozzles limit the use to synthetic AFFF only.
Non-air aspirating nozzles are used in a cone pattern by firefighters to push the products of combustion ahead of it and out of a structure opening due to the amount of air (oxygen) that is drafted into the discharge stream. Therefore, when cone patterns are used to apply the foam extinguishing agents onto an exterior flammable liquid fire, more oxygen is drafted into the fire area. This intensifies the fire and the resulting effects are similar to a blast furnace. The aircraft within the fire area, as well as the passengers inside, receive the full impact of this new generated heat.
* The practical critical area Is the pre-determined point, based on given factors, that must remain fire tree to allow a successful rescue operation.
Under normal exposure to a flammable liquid fire, the skin of an aircraft fusilage will burn through in approximately two minutes. Now, the non-air aspiration nozzles cone pattern is forcing all the heat directly against the aircraft’s exterior skin and accelerating the destruction of the only means of isolation from the flames. The passengers’ chances of survival have again been reduced, if not eliminated entirely.
Remember, it is the extinguishing agent that fights the fire. The person who operates the device only applies the agent(s). It is the operator’s responsibility to know the characteristics of the available extinguishing agents. The more efficiently the operator applies these agents, the better his chances of saving lives.
The most effective extinguishing agents in combatting spill fires are the primary agents: AFFF, fluoroprotein, and synthetic nonaqueous foam concentrates. Agents required to complement these are dry chemical (potassium bicarbonate) and halogenated agents vaporizing liquids (HALON 1211).
Protein foam and dry chemical powders have been available only since the 1940s. This explains why firefighting teams did such a poor job of extinguishing aircraft fires prior to this.
The problem was simple. The dry chemical powder was a sodium bicarbonate that was not compatible with protein foam. Also, protein foam bubbles picked up fuel when plunged into the fuel, and the bubble burned. Combining these two deficiencies made extinguishing an aircraft fire very difficult, especially with the higher fuel vapor pressures compared to the fuels used in commercial aircrafts today.
Today we have new problems. AFFF extinguishes flammable liquid fires by the active ingredients draining from the foam bubble and forming an aqueous film on top of the fuel.
AFFF foam bubble is not the medium of extinguishment, but the solution that drains from the bubble extinguishes and secures the fire area. That is why lower expansion ratios are used with AFFF—to speed up the solution drainage.
The active ingredients flow over the fuel surface at a specific spreading coefficient. Once the surface has been covered, fuel vapor suppression should occur.
The problem we have is related to movement. If the fuel is flowing, then the film will float away on top of the fuel. Therefore, the securing feature of AFFF will not remain in the practical critical area to provide a fire free escape path. This necessitates a more continuous application of foam onto the practical critical area. If there was an ample available water supply for foam production, this would not be a problem. However, the supply of water is limited to the number and carrying capacity of the CFR vehicles.
If an aircraft comes to rest on the runway or taxi-way leaking fuel and on fire, rescue personnel will have great difficulty putting out the flammable liquid fire with AFFF unless all sources of ignition are extinguished on initial attack.
The sources of ignition that AFFF does not extinguish are burning aircraft tires, magnesium wheel assemblies, or other combustible metals that burn more aggressively when water /foam solutions are applied.
So, how do we correct this situation? We make sure to have available foaming agents with different extinguishing characteristics, such as fluoroprotein. Fluoroprotein foam solution extinguishes flammable liquid fuel fires by developing a cohesive foam blanket that will cling to rough runway surfaces and to aircraft tires. This helps prevent fire spread.
Combustible metal fires can only be contained because in most cases the solution draining from the foam bubbles intensifies the flames. Also, synthetic non-aqueous foam concentrates applied through air aspirating foam nozzles with a 50-75:1 expansion ratio can provide a deep, slow draining foam blanket.
This application can only be applied using hand lines. Fluoroprotein and synthetic non-aqueous foams rely on the foam bubble structure to extinguish the fire, but AFFF relies on aqueous film forming characteristics. This is why it is essential that more than one type of foam concentrate be available in the CFR vehicles.
How do we combine two different foam agents in aircraft firefighting operations? If your present fleet is equipped with non-air aspirating foam monitors/nozzles, replace them with air aspirating foam barrels with deflector tips that will generate foam using fluoroprotein concentrate with an expansion ratio of 7:1 to 9:1. The same design features will also allow AFFF to be applied with an expansion ratio of approximately one unit higher, 8:1 to 10:1.
Changing to an air aspirating foam applicator with a stream deflector jaws will improve operator performance in two ways. First, the operator is forced to stay back from the edge of the fire and elevate the foam applicator to a minimum of 10° above the horizontal. This allows the foam to flake down onto the fuel and extinguish the fire without disturbing the fuel.
The same application technique applies to both AFFF and fluoroprotein. By using AFFF initially, you will knock down the fire about 30% more quickly than using fluoroprotein. Once the fire is knocked down, switch your foam selector to fluoroprotein and continue securing the practical critical area because the rescue operation could be prolonged for some time, depending on the number and mobility of trapped occupants. Fluoroprotein provides a longer, more stable protective blanket.
Most crash trucks are equipped with a foam liquid concentrate tank with sufficient capacity to supply two tanks of water. Redesign the tank with a partition. This will provide sufficient space on one side for fluoroprotein concentrate for one tank of water and the other side for AFFF concentrate. Then add linkage to the twin foam selector valve that will allow for only one foam concentrate being inducted at a time.
Assuming the aircraft is on fire (exterior flammable liquid fire) on arrival, attack the fire with AFFF. As soon as the fire is knocked down in the practical critical area, switch to fluoroprotein and secure the practical critical area with a cohesive free flowing foam blanket.
To maintain a secure flammable liquid spill area using fluoroprotein, foam should be periodically applied approximately every 10 minutes depending on the rescue traffic and weather conditions.
New CFR vehicles should be designed with a split foam tank. There are two reasons for this: To provide more flexibility in the use of products available today and to allow for the progressive introduction of any new foam concentrates that may be available in the future.
The use of dry chemical and halogenated agents, which complement the foam agents in extinguishing horizontal flammable liquid fires, are vital to the success or failure of the operation.
Unfortunately, airline operators are reluctant to use these agents (specifically dry chemical) because of the effect potassium bicarbonate may have on the aircraft. In fact, their concerns have greatly affected the availability of these agents.
This is unfortunate because dry chemical, especially, is essential and necessary to extinguish three dimensional or running fuel fires. It is a proven fact that, when applied simultaneously, AFFF and dry chemical (potassium bicarbonate) can effectively eliminate more cubic fire area than when they are applied separately.
Visibility for exiting passengers is another concern. If given a choice, passengers would prefer to exit through a cloud of dry chemical, rather than through a wall of fire.
Frankfurt International Airport in Germany has a response vehicle that carries 12,000 kg (25,000 pounds) of dry chemical powder. However, airport personnel there are concerned about the effect that dry chemical may have on the involved aircraft. They also rely on AFFF to solve all their aircraft firefighting problems.
That’s why protection standards are now calling for only 500 kg (1,000 pounds) of dry chemical to combat a Category 8 and 9 aircraft, which has engines located three stories in the air. Every CFR vehicle should carry at least 500 kg (1,000 pounds) of dry chemical for three dimensional fires.
Halogenated agents, specifically HALON 1211, has been proven effective on engine fires, cabin fires (in limited quantities), and fires in difficult areas (i.e. baggage compartments).
A fire involving an aircraft on the parking ramp normally has first aid extinguishers available for immediate use on small fires. In this case, you should use HALON 1211. However, if flammable liquid fuel spill is involved, potassium bicarbonate dry chemical should be the agent you use.
The firefighting team should arrive at the accident scene with a pre-conceived plan: First, to extinguish visible ground fires in the practical critical area and, as soon as visibility improves, to extinguish all three dimension fuel fires using dry chemical.
TACTICS
The second most important aspect to consider after the extinguishing agent’s characteristics is the tactics you will use on the scene. In the past, the tactic using protein foam was to insulate and isolate the aircraft fusilage from the effects of fire. With the introduction of new foam agents (AFFF), the tactic became known as total extinguishment.
Using a non-air aspirating nozzle could change the width of the foam stream pattern and provide more active ingredients over a wider fuel area. The non-air aspirating foam is very fluid and flows around obstacles more quickly than the cohesive foam that is produced with protein. However, non-air aspirating foam causes problems, as we discussed earlier.
Nevertheless, the aircraft fusilage fire-resistant qualities have not been improved over the years. Fire still burns through the skin of a passenger aircraft in approximately two minutes.
Therefore, the first concern of rescue personnel should be to move the fire away from the fusilage. This can be done using the aircraft fusilage as the aim point and insulating the skin, thereby reducing the temperature of the metal and extending the life of the fusilage.
The free flowing AFFF foam will rapidly run down the side of the aircraft onto the flammable liquid that is pooled near the aircraft. This will extinguish the fire and, in effect, move it away from the fusilage. As the foam continues to flow over the fuel, it will further isolate the fire, helping to extend the life of the aircraft fusilage’s outer skin.
The foam stream pattern can then be progressively widened by depressing the jaws on the foam barrel. This reduces the reach of stream, further moving the flames away from the primary concern (which is the occupants) until the practical critical area is secured.
Once the fire in the practical critical area has been knocked down, you should switch the foam agent for initial attack from AFFF to fluoroprotein. This will help secure the practical critical area and prepare for the long rescue/salvage operation.
Three dimensional fires should be attacked with dry chemical as soon as they can be located (engine and wing areas) and extinguished using sufficient high flow nozzles. Remember that the longer these types of fires are allowed to burn uncontrolled, the more of the limited water supply for foam production that will be consumed. Also, if ignored, a wing can burn off, allowing tremendous amounts of fuel to escape just when most of the practical critical area has been secured.
The potential problem with complementary agents in the limited quantities presently recommended for use on an aircraft is the manpower that is required to remove the hose lines and attack the fire. All CFR vehicles are designed and built with a roof mounted turret plus a pre-connected hose line, one on either side of the vehicle.
Again, one-man operated vehicles cannot meet the tactics needed to provide adequate fire extinguishment capability. In this situation, sufficient dry chemical should be available to be dispensed through a twin roof mounted monitor.
There has been only one operational fire performance test of products that simulated a real aircraft. This was conducted by the Federal Aviation Administration (FAA) at Edward Airforce Base in Washington, D.C., using a Boeing 720 aircraft loaded with anti-misting fuel. Because the aircraft did not crash as it was supposed to according to the test design, it caught fire and burned. Present standards call for only 8,500 liters (2,245 gallons) of water for foam production. This fire department used 90,000 liters (30,000 gallons).
In the Boeing 737 aircraft fire at Manchester, England, approximately 45,600 liters (12,000 gallons) of water for foam production was consumed.
In the DC-9 fire at the Cincinnati, KY, Airport, approximately 37,000 liters (10,000 gallons) was consumed. This fire was a total interior fire. The fuel on board never became involved.
The Cincinnati DC-9 fire presents a forgotten and undetermined requirement concerning aircraft fires. The total firefighting package reflected in any standard for aircraft firefighting or tactics is based on a flammable liquid fuel fire, not interior cabin fires. There have been no calculations or tests conducted to determine the interior firefighting requirements.
If interior firefighting was considered, it would be necessary to review the design of all the aircraft firefighting vehicles. This could result in CFR vehicles being equipped with special hydraulic powered ladders in order to increase safe access to the exits. It could also lead to the following improvements: special foam firefighting nozzles, such as medium expansion foam nozzles (50-75:1 expansion ratio), and a sufficient number of firefighters to handle the nozzles and gain access to over wing exits or the main exits that are not being used by exiting passengers.
The other issue that must be considered is the discharge pressure of standard handline air or non-air aspirating foam nozzles. These nozzles operate at discharge pressures of 75-125 psi. Such high pressures could cause physical injury to trapped aircraft occupants. Therefore, medium expansion nozzles are what you should use for interior firefighting because this principle of extinguishment is volume application at low nozzle pressures.
SUMMARY
It is easy to criticize a system, but in this case it seems justified, as recent aircraft accidents have proven that the system is not as prepared as the average passenger believes. Two minutes to live is all one has once an aircraft is enveloped in a flammable liquid fire. If it is an interior fire, one has less than two minutes.
We need to make decisions today that will improve the public’s chances of surviving an aircraft accident tomorrow.
