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/ / / / NPEO 2014 Volume 2 Issue 3 (June)

Fire Suppression

A fire at sea is something few have to deal with. It could occur hundreds of miles from land with no help in the immediate area. Ships need to be equipped with proper firefighting systems to battle such disasters and extinguish the threat before it gets out of hand.

The Navy has a variety of systems in place to fight fires that have started at sea, said John Farley, director, Chesapeake Bay Detachment/ex-USS Shadwell Fire Test Operations at the Naval Research Laboratory’s (NRL) Navy Technology Center for Safety and Survivability. The ex-USS Shadwell is a decommissioned U.S. Navy landing ship dock now used to study the latest technologies, techniques and doctrines in maritime firefighting.

Shipboard firefighting systems currently being used include gaseous agents (Halon and HFC-227ea), aqueous film forming foam (AFFF), water mist and miscellaneous seawater sprinkler systems he said.

The gaseous agents and water mist are generally used to counter class B (flammable liquid) fires in machinery spaces and flammable liquid storerooms. Due to the Montreal Protocol and subsequent U.S. law, Halon extinguishing agents are being phased out and now the preferred machinery space agent is water mist. Currently, HFC-227ea is being used for engine enclosure and flammable liquid storeroom fire protection applications, said Farley. Gaseous agents are stored within pressurized gas cylinders, and the gaseous agents are dispersed into the protected space via a distributed piping/nozzle array.

AFFF is also used to counter class B pool fire threats on the flight deck, pump rooms, hangar bays, and some large volume spaces such as well decks and vehicle storage areas. AFFF concentrate is mixed with seawater from the ship’s firemain system at the AFFF proportioning pump locations and is dispersed to the protected volume via a distributed piping/nozzle array.

The water mist systems use high pressure pumps, which are fed from a dedicated fresh water supply source and disperses the generated fine water mist droplets into the protected volume via a distributed piping/nozzle array.

Seawater sprinkler systems are used to protect magazine (ammunition storage) spaces and are used in some high class A (combustible solid) fuel load spaces, such as berthing areas or storerooms. The miscellaneous seawater sprinkler systems are serviced from the ship’s distributed firemain system, which directs seawater to the various piping systems and nozzles that are located within the desired protected spaces.

High expansion (HiEx) foam and self-contained aerosol generators are two additional fire suppression technologies that have been recently introduced into the fleet. HiEx foam generators are used to protect the Joint High Speed Vessel mission bay and machinery spaces. The self-contained aerosol generators will be used as a Halon alternative for the Navy’s Ship-to-Shore Connector and on the Navy’s Landing Craft Utility.

HiEx foam concentrate is mixed with seawater from the ship’s firemain system at the HiEx proportioning pump station and is dispersed into the protected volume using specialized HiEx foam generators. The HiEx foam generator uses a fan to generate an air flow, which essentially pushes the HiEx foam solution against a screen to generate the HiEx foam bubbles.

A self-contained aerosol generator is essentially a small hermetic sealed unit that contains a solid potassium-based solid compound, which when activated will disperse a very fine aerosol into the protected compartment. Since the technology is totally self-contained, it does not required any pressurized cylinders or pumps for its operation, and negates the need for any piping/nozzle array system for agent distribution.

Ron Roller, force damage control officer on the staff of Commander, Naval Surface Force, U.S. Pacific Fleet, said that ships of all sizes have salt water sprinklers, Halon, HFP (Heptafluoropropane), AFFF, water (salt and potable), and aqueous potassium carbonate (APC).

“All ships have different variations of saltwater sprinkler systems in berthing and habitability areas,” said Roller. “Some are manually activated through various directional valves while others are automatic through thermo heat devices. Salt water acts as a cooling agent for fires, mainly used on Class A [regular combustible materials] fires.”

Newer ships such as the littoral combat ship (LCS) 1 and 2 variants and the LPD 17 class (amphibious transport docks) have water mist fire extinguishing systems (WMFES).

“The WMFES is a relatively new fire suppression system used on newer ship classes in engineering spaces,” said Roller. “WMFES uses sprinkler heads made up of many very small nozzles releasing high pressure de-ionized water into the space, creating a mist acting to cool and smother the fire. WMFES is beneficial since the affected space does not have to be immediately evacuated, providing more time for initial fire fighters to combat any localized fire(s). The cooling effect also aids in the firefighting team’s re-entry of the space.”

Roller added that older ships use a carbon dioxide (CO2) flooding system.

“Installed CO2 flooding systems are still used on some older ships due to original ship design,” he said. “Newer ships no longer use installed CO2 suppression systems due to the inherent danger as it completely and quickly displaces all life-sustaining oxygen from a space.”

Both Farley and Roller said there are several challenges when fires occur at sea.

“First, there is nowhere to run, which requires the ship’s crew to quickly contain the [fire], and second, there is a need to maintain and/or restore the ship’s war fighting mission,” said Farley. “Other factors that contributes to this challenge is the fact that beyond the presence of a large quantities of flammable liquids and unique compartment geometries, which may include highly cluttered spaces, the warship also has stowed ordnance present, and always has the obligation to go into harm’s way when called upon.”

Roller said that smoke control is also a challenge when combating a fire at sea.

“All fires generate toxic gases through smoke that can spread quickly to other shipboard spaces,” he said. “Securing ventilation and the setting of both fire and smoke boundaries is paramount in getting the fire and smoke under control. Fires under control significantly mitigate the possibility of spreading to other spaces.”

He added that certain types of fires are more difficult to suppress such as [fires located in] engineering spaces on conventional steam generation ships that pose risks due to the many heat sources located within. Magnesium metal fires (sometimes used in aircraft wheels) also pose a significant challenge as the metal is an oxidizer and does not react well to conventional firefighting techniques and practices.

Additionally, a deep fat fryer fire in the ship’s galley is especially dangerous since any application of water can create a violent explosion of steam, pronouncing fire effects dramatically. Use of the ship’s deep fat fryer is interlocked to the aqueous potassium carbonate (APC) fire suppression system for safety purposes. “APC is an automatic fire suppression system used for shipboard deep fat fryers in the crew, wardroom and flag galleys and is a liquid form of the more commonly known Purple K Powder, a portable dry-chemical fire suppression agent used to smother class B fires,” said Roller.

He added that the biggest fire dangers aboard a ship at sea are flammable oil systems leaks, standing oil in engineering spaces, oil spray fires, air capable ships’ fixed wing and helicopter operations, general housekeeping and ventilation cleanliness. He added that crews train for these potential threats on a regular basis. “Shipboard fire drills are common practice and conducted on a continual basis,” he said. “Shipboard training teams are highly trained and established to conduct drills during any condition, including while underway, in port, during industrial availabilities, etc. There are many case studies resulting in lessons learned, but we are still learning.”

Look Ahead

Farley said the NRL is currently working on a number of projects that include the use of “portable” high expansion foam generators in the event there is a shipboard fire that is unconfined and fire conditions circumvent effective manual response firefighting operations. Secondly, they are looking into the use of fixed AFFF/water cannons (both autonomous and/or remote manual operations) for large volume mission critical space fire protection. The NRL is also investigating the efficacy of using fluorine-free class B foams in lieu of AFFF at some point into the future, as well as verifying that any proposed alternative mobility and/or jet fuel does not comprise the effectiveness and/or increase the fire risk for current fire extinguishing agents.

“There is a tremendous push right now to identify the hazards posed by lithium and lithium ion batteries that are being used for a number of Navy applications,” said Farley. “Most of the work to date has focused on quantifying the fire/explosion potential, heat release rate, and toxic gas hazards posed by some of the battery chemistries, and to look into additional battery storage safety issue requirements. Knowledge gaps still exist related to lithium battery firefighting media effectiveness, which will require additional experimental study.”

Roller said that there are many improvements aboard the LCS and DDG 1000 platforms to be implemented in 2014, including many innovative and technology-driven systems incorporating automated fire suppression systems, remote control extinguishment, shipboard cameras, and less manpower driven monitoring, to name a few. The WMFES is a prime example of such advancements, he added.

“We continue to use lessons learned and case studies in future development of policy and procedures for combating shipboard casualties,” he said. Drew Marine has been providing the U.S. Navy’s support fleet components, services, and engineering/technical support, for a variety of fire suppression functions and activities onboard Navy ships, said Gerald Lodge, fire, safety and rescue (FSR) technical marketing manager at Drew Marine. Specific systems include high/low pressure CO2, firefighting foams, dry chemical powder, Halon and clean agent gas, sprinkler, and water mist systems.

Platforms using Drew Marine services within the U.S. Navy surface ships include rescue and salvage, combat support, amphibious command, guided missile destroyers, landing and dock vessels, amphibious transport docks and joint high speed vessels, to name a few.

Each specific system has its own unique function and suppression capability; the customary method of fire suppression involves a direct interference (and thus break-up of the fire cycle), said Lodge. Disrupting the fire cycle is chemical in nature for gas and clean agent systems, while involving a cooling effect in the water-based systems. With foam-based systems, a smothering effect becomes the primary mode of suppression, as the agitated foam solution spreads across a liquid fire and cuts off the various legs of the fire triangle, which include oxygen, fuel and heat or ignition, he said.

“The complexities of each system type differ,” said Lodge. “We ensure working systems and consistency via planned maintenance and testing, annual inspections, services, and training. Drew Marine also utilizes its ties with major operators and regulatory agencies for additional inspections, repairs and certifications.”

Drew Marine is involved in ongoing initiatives that involve fire suppression, as well as an overall FSR suite of products and services. Many of these improvements have been initiated by feedback received from end users, their service engineers/technicians, or are based on input from their Firefighting Foam Analysis Laboratory and Technology Center.

“For instance, we are working within several different ship classes on replacing obsolete galley fire suppression systems, in addition to updating the fire detection systems,” said Lodge. ♦

 

Last modified on Thursday, 03 July 2014 13:30

Additional Info

  • Issue: 3
  • Volume: 2
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