Aircraft carriers are wonderfully engineered floating and portable airports. Not many countries have them in their fleets and of those who have, usually have no more than one. The exception is the United States Navy with 10 Nimitz-class supercarriers on their fleet. As with most military topics, public information on this subject is scarce or inexistent. Thus, this article is about fire fighting on the American aircraft carriers‘ flight decks, which are the only carriers about which, after some digging, information is available.
A Moving Airport
On conventional airports (military, civilian or of mixed use) everything is as far apart as possible for safety reasons. There are minimum separation distances between runways and taxiways, between aircraft parking spots themselves and terminal buildings, etc. Plus, fuel farms are taken as far from the operational areas as possible and ammunition depots in military aerodromes have tight security and safety measures for obvious reasons. The people working on the apron have their movements restricted and carefully monitored in order to avoid accidents and damage to aircraft, the infrastructure or themselves.
Forget everything you’ve read in the paragraph above… Aircraft carriers have limited space and still have to meet the needs of an airport. On an area of about 4,5 acres (196 020 sqft or 18210 m²) all the magic happens.
The Nimitz-class carriers’ flight decks are 1092 feet (332.8 m) long and 252 feet (76.8 m) across at their maximum width. There is only one paved runway on the world that short, on the island of Saba, in the Caribbean, at 1000 feet (304.8 m). However, the carriers’ landing area is even shorter (800 feet or 243.8 m), given that it is angled, therefore the need for arresting cables and the use of catapults for take-off.
The problem with an aircraft carriers’ flight deck is that everything has the potential to be up there or to end up there: lots of aircraft (fixed-wing and helicopters) moving or parked within inches of each other, some loaded with fuel; lots of ordnance stored in an area called the bomb farm, in the starboard side of the island, or mounted on departing or arriving aircraft; lots of people working and moving to make the operations possible; some vehicles for aircraft assistance and safety, including a salvage crane, a crash forklift, vehicles for moving ordnance around, and two fire-fighting vehicles; lots of fuel being pumped in and out of aircraft; lots of hazardous liquids such as liquid oxygen or hydraulic fluids…. Not to mention that aircraft carriers are weapons facing enemies, which could eventually strike. Mix all these factors with really high tempo operations, where everything is done in dangerously close proximity to everything else and as fast as possible and you end up with a volatile environment, full of dangers for people and everything else.
There are several lines of defense against (aircraft) fires in a flight deck, the first one being common sense and carefulness of all those men and women working in the area. Another line of defense is the development of better protection systems for ordnance so that bombs and/or rockets do not cook off and get activated by excessive heat, movement or exposure to the elements.
The second line of defense is a set of 22 hose stations placed around the deck. These stations are formed by two sets of hoses: a 1.5 inch (3.8 cm) hose reel that allows AFFF (Aqueous Film Forming Foams) to flow directly to the nozzle and can be deployed extremely fast, and a 2.5 inch (6.3 cm) soft hose mounted on a rack, which can be plugged to a hydrant providing AFFF or to a hydrant providing Sea Water, which would be used to fight only class-A fires, which are quite unlikely to happen at a flight deck. There are also stations providing CO2 and PKP (one of many kinds of dry-chemicals) fire extinguishers along the deck perimeter.
It is important to mention the need for the dual placement of hoses on the port and starboard side for a number of reasons: picture that there is a series of aircraft blazing in flames on the port side. Due to the massive heat and explosion danger, no one would be able to access the hose stations on that side, next to the burning aircraft. Hence the need for hoses long enough to fight fires on the other side of the ship. Another reason is the fact that several aircraft can be parked in front of a station, not allowing the team with the hose to get to the area of interest fast and safely enough. Plus, the wind conditions have a deep influence in how a fire is fought, making the need for alternatives essential.
The number of sailors manning a hose line is regulated with a maximum and a minimum. The maximum number exists for two reasons: autoprotection, in order to avoid losing too many men who are working on a line from a blast; and operativity, in order to avoid the hose line from not being flexible and dynamic, which would hinder the fire-fighting capabilities. The number of hoses for every flight deck fire is also regulated and has to be of at least four.
Another line of defense is the dedicated fire-fighting team at the flight-deck who can always be seen sitting on a vehicle called the A/S32P-25 (P-25 for short). This vehicle moves around the flight deck and is positioned strategically to have the ability of a rapid response in case of an aircraft fire.
Given that it has a high-pressure turret, a water (750 gallons – 2840 L) or an AFFF (50 gallons – 190 L) tank, a pump and a dedicated team (the Crash and Salvage team), it can provide much-needed initial response capability, due to its mobility and the pump-and-roll capacity, meaning that it can discharge the turret while rolling in on a fire. It can also be supplied with an external source both of water and AFFF so that it can pump it through the turret for as long as they are provided.
The P-25 also carries four 20-lbs halon 1211 fire-extinguishers for small internal engine or avionic compartments fires. A visual description of all the elements onboard a P-25 can be seen in the next picture.
The last line of defense on the flight deck is what is called a “wash-down system“. A wash-down system on a Nimitz-class carrier is a series of flush-deck nozzles mounted on the deck, the flight deck perimeter and the four elevators. These nozzles discharge up to 27000 gallons per minute (1700 L per second) of water and AFFF to flood the deck in case it is necessary. However, the system was designed in a way that allowed only the affected areas to be washed-down: the flight deck is divided in 20 smaller areas which can be activated separately from the Primary Flight Control and the Navigation Bridge.
The periodic discharge of AFFF onto the flight deck is required, as well as an analysis to ensure that the ratio betwen seawater and AFFF concentrate is optimal.
Emergency Procedures and the Importance of Drills
Anyone next to a fire is expected to fight it, either using a portable extinguisher or the AFFF hose reel. Then, the mobile fire-fighting vehicle (P-25) could arrive before the man who is carrying the first extinguishing tool. Afterwards the hose teams respond, as explained before. Obviously, fueling operations would cease and fuel pumps would be secured, just in case. If there were pilots or members of the crew in need of rescue, the Hot-suit men would be available for rescue.
All this would happen on the flight-deck, but on the island, additional measures would be applied: first, the ship would manoeuver for favorable wind and the Air Boss would activate the AFFF wash-down system if the fires were beyond capability of being extinguished by the hose teams. He would activate the fire area and the areas upwind of the fire.
Uninvolved aircraft would be moved away, as well as ordnance and carts with flammable liquids. Ordnance would be cooled up to 15 minutes after the fire was extinguished.
Once the fire had been extinguished, salvage operations a clean up and a FOD (Foreign Object Debris) walkdown would be performed to have a “ready deck”
The Path to Safety
Unfortunately, to reach this level of protection and safety-conciousness, there have been several disasters which have shaped the mind of the sailors and the officers, the protection measures needed and the way things are done when fire incidents occur.
During World War 2 many aircraft carriers (see USS Essex for example) were damaged or sunk due to kamikaze , U-boat or surface attacks by the enemy. It would have been very difficult to save the ships from a fire-fighting point of view, since what would have kept the carriers from going under would have been greater hull protection. The loss of life was terrible.
In 1967, the USS Forrestal disaster killed 134 sailors after a rocket discharged on the flight deck and the ensuing fires and blasts killed the fire-fighting team, who were using correct fire-extinguishing agents. Other sailors did not have proper fire-training and were killed from blasts or by advancing fire as some of them were using seawater as an agent, without nowing that would make things worse, as water and class B fires don’t go well together. The situation forced the sailors to improvise.
After the Forrestal disaster, the US Navy decided to take action to prevent any similar incidents to take place: wash-down systems were installed and mandatory fire-fighting training was given to all sailors, to avoid the improvisation seen on the Forrestal from happening again. A film was produced and shown, as part of the training: Trial by Fire: A Carrier Fights for Life.
Other incidents have happened since the Forrestal, but none so destroyful or lethal.
Aircraft Carrier Flight and Hangar Deck Fire Protection: History and Current Status, by R. Darwin; H. Bowman, M. Hunstad, W. Leach and F. Williams.
NATOPS US NAVY AIRCRAFT FIREFIGHTING AND RESCUE MANUAL