The Naval Research Lab's Technology Center for Safety and Survivability develops and tests cutting-edge technologies that involve combustion dynamics modeling, fire extinguishing agent development, fuel analytics, firefighting doctrine development and more. The center operates two specialized fire research facilities that include the Chesapeake Bay Fire Test Detachment (CBD) located in Chesapeake Beach, Md., and the full-scale fire test ship, the decommissioned ex-USS Shadwell (LSD 15) located in Mobile Bay, Ala. The ex-USS Shadwell is regularly set ablaze in a controlled environment to advance the safety of operational Navy and civilian shipboard firefighting.
Every Sailor is a firefighter first, and a large portion of basic training is dedicated to firefighting, damage control and prevention tactics because a fire aboard ship can be catastrophic for the ship and crew. The Navy is continuously researching and developing new technologies to protect the fleet and Sailors.
John P. Farley, director for Shadwell/CBD test operations, discussed NRL's research, development, test and evaluation efforts in improved firefighting technologies in a written response to questions in May.
CHIPS: The development of aqueous filmforming foam in the 1960s by NRL benefited the Navy, and it is now used in many civilian settings. What are the unique properties of AFFF?
Farley: As the name implies, AFFF enables the formation of an extremely thin layer of water, a few tenths of a millimeter, to form between the liquid fuel and the foam blanket. This aqueous film barrier helps to prevent the fuel vapor and oxygen from mixing, which is needed to support combustion.
Of course the question then becomes: how does one get a water film to float on a liquid hydrocarbon fuel surface? This feat is achieved due to the key ingredient of AFFF, which is a fluorinated surfactant. The fluorinated surfactant lowers the surface tension property of the water and enables, as the water drains from the foam, the formation of the aqueous film that floats on top of the liquid fuel surface.
Because of the superior fire extinguishing performance capabilities of MILSPEC (military specification) AFFF, it has become the agent of choice whenever there is a Class B (flammable liquid) hazard present both in the military and the commercial sector. The next time that you see a vehicle fire, a train derailment [or] refinery fire on the news, or traveling through an airport both here and abroad, you can be self-assured that MILSPEC AFFF is on the scene.
CHIPS: NRL research resulted in advances in shipboard firefighting using high expansion (HiEx) foam systems. How will HiEx systems change firefighting on Navy ships?
Farley: A high expansion foam system utilizes a series of fixed foam generators that are generally located high in the compartment. A nozzle within the generator sprays a foam solution against a screen which then forms foam bubbles that flow into the protected compartment. In some respects this is the same principle used when a child generates bubbles with a handheld wand.
The advantage of a HiEx foam system over a conventional overhead sprinkler system is that the foam generated is 3-D capable; that is, it expands to fill a large volume in minutes, flowing around any obstructions enabling complete extinguishment of a fire that is independent of the type of fuel load present.
These noted advantages are particularly important to the Navy when considering the type of fuel loads that may be present in large volume mission critical spaces, such as a hangar bay, well deck, or vehicle storage areas. A large uncontained fire in one of these types of spaces could quickly lead to a ship conflagration, which could directly impact the ship's warfighting capability.
A HiEx foam system provides a 'quick response' solution that will not need a manual firefighting back-up response that is typically required for a ship fitted with conventional overhead sprinklers. This fact in itself is important because a rapidly growing fire in a large volume, highly cluttered space would pose significant manual firefighting challenges even for a seasoned professional firefighter.
CHIPS: Long before the mandate in 1987 (Montreal Protocol on Substances that Deplete the Ozone Layer) to halt production of halons by 1994, NRL began research into halon replacement. What are some of the halon-free fire protection options that NRL transitioned?
Farley: In the fire protection community, we typically note halon substitute technologies as either replacement options or alternatives. Replacement options include gaseous agents. For the most part these replacement agents are halogenated hydrocarbons that have low ozone depletion potential (ODP). The NRL proposed Halon 1301 (CF3Br) replacement was heptafluoropropane HFC- 227ea (CF3CHFCF3), which the Navy calls HFP. HFP is currently used for engine enclosures or flammable liquid storeroom applications. For halon alternatives, NRL recommended the use of water mist and self-contained aerosol generator technologies.
Water mist systems create a fine mist of water droplets, allowing the use of smaller quantities of water than conventional sprinkler systems. Due to their ability to quickly absorb heat, the water mist systems are found to be very effective for machinery space applications. Water mist systems are now employed on the LPD 17 class (amphibious transport dock ship), LHD 8 (amphibious assault ship), LCS (Littoral Combat Ship), the DDG 1000 (destroyer) and the U.S. Coast Guard National Security Cutter.
Aerosol generators on the other hand distribute micron-sized dry chemicals that interrupt the chemical chain reaction of a fire. Aerosol generator technologies have been found to be very effective for those applications where a low weight and low cost alternative is paramount to the fire protection design.
CHIPS: The Navy is developing a new vessel, the Ship-to-Shore Connector, to replace the landing craft air cushion. Can you talk about the firefighting systems on the SSC vessel?
Farley: The SSC fire protection design was particularly challenging because the SSC design, like the existing LCAC, is extremely weight critical, and the operating parameters include the need for a fire protection strategy that can operate in a temperature range of 10 to 200 degrees Fahrenheit. It was determined that the aerosol generators were the best Halon 1301 alternative system for the SSC gas turbine engine enclosures, auxiliary power units and fuel bay. The aerosol units enabled a 70 percent reduction in weight, were inexpensive, and also enabled a maintenance-free solution since the aerosol generators have a 10-year shelf life.
For the SSC Cargo Deck, the best Halon 1211 alternative turned out to be a 150-pound monoammonium phosphate dry chemical ABC extinguisher. [An ABC fire extinguisher can be used on three different kinds of fires: Class A (ordinary combustibles such as wood or paper), Class B (flammable liquid fires such as grease or gasoline) or Class C (electrical fires)].
It should also be mentioned that the successes of the SSC Halon alternative program led directly to transitioning of the aerosol generator technology to the U.S. Navy Landing Craft Utility for diesel engine room and flammable liquid storeroom protection. There is also considerable interest in the aerosol generator technology by the U.S. Coast Guard for potential use on the new National Security Cutter and Utility Barge application.