^ Fire @ Scandinavian Star in 1990 Triggered Revision of IMO Regulations (Source: http://www.imo.org/OurWork/Safety/FireProtection/Pages/History-of-fire-protection-requirements.aspx)
Of Ships & Fires
Fire is a good servant but a bad master. Nowhere is this more true than in raging infernos onboard ships. Fires in buildings are bad. Those on ships are terrible inflicting grave losses to life, limb, environment, millions-worth property, and invaluable port operations.
Watertight and metallic, ships expedite rapid heat buildup and structural deformity during fires stacking the odds heavily against the firefighters. Plus, there is the complex layout, maze of watertight doors, and vertical ladders convoluted by open hatches, bulkhead projections, and raised sills.
According to the report Occupational Accidents Aboard Merchant Ships by H.L. Hansen et all., crews aboard roll-on-roll-off (RoRo) and coasters (general cargo ships) are most accident-prone. An overwhelming 80% of maritime casualties result from human factors.
Onboard Fires & Anti-Fire Regulations
Ships face onslaught from:
- Cargo Shift: stability-disturbing change in cargo orientation
Fire is classified based on the material it burns:
- Class A: wood, upholstery, glass-fiber, furnishings
- Class B: liquids viz. fuels, lubricating oils
- Class C: gas viz. LPG
- Class D: metals viz. aluminum, magnesium
- Class E: high-voltage burning of any of the above
SOLAS Chapter II-2 (that deals with fire safety on ships) focuses on the fire-scenario process. Starting with fire prevention and detection, it moves to suppression and evacuation. Authorities shifted technical requirements to the new International Fire Safety Systems (FSS) Code for simpler interpretation.
Functional prescriptions under this chapter:
- thermal and structural demarcation of the ship into main vertical and horizontal zones as well as in accommodation/non-accommodation areas
- minimal use of combustible material
- minimizing possibility of volatile cargo-vapor ignition
- detecting fire in its zone of origin
- containing and extinguishing fire in its space of origin
- ready availability of fire-extinguishing equipment
- protection of means of escape and access to fire-fighting instruments
Combating Onboard Fires
To start and strive, fire requires four essentials called the fire tetrahedron:
- combustible substance
- ignition source
- combustion chain reaction
Remove one, and the fire douses. Absence of any one prevents fire.
Fighting fires involves its detection-location, alarm, and extinguishing. Direct attack on established fires deep inside the hull constitutes unjustifiable risk for the firefighter’s life and health. Cut off air supply by locking the area to stamp-out below-deck fires. Use water sparingly as it cannot extinguish all fires and its load lowers the vessel’s stability.
Machinery-space fires are particularly annoying for evacuation of these areas causes treacherous loss of navigation control. Neglected oil leakages onto hot exhaust manifolds start many such fires. These start small, something vigilant watch-keepers can nip in the bud. Unmanned machinery spaces require efficient detection-alarm systems.
Fire-Fighting equipment types:
- Small Portable Extinguishers fight small, localized fires
- Large Fixed Systems resist large, rapidly-spreading fires. Use these after evacuating the affected area
All portable fire extinguishers are pressure vessels requiring regular maintenance checks:
- CO2 Extinguisher: stores liquid-CO2 that becomes gas while leaving the container. Used to stamp-out Class B and C fires in electrical equipment in machinery spaces, it is not used in accommodation areas for CO2 suffocates humans
- Soda Acid Extinguisher: uses pressurized CO2 generated by mixing sodium-bicarbonate and sulphuric acid. It drenches Class A fires
- Dry Powder Extinguisher: uses sodium-bicarbonate powder forced out by CO2 It does not provide cooling effect. Usually located near electrical equipment, it suppresses all classes of fires
- Foam Extinguisher: chemical types utilize pressurized CO2 created by mixing sodium-bicarbonate and aluminum-sulphate. Mechanical type employs water-foam mixture to force out the stored CO2. Located near flammable liquids, these quell Class B fires
Fixed installation extinguishers fight established fires which portable extinguishers cannot suffocate. They must be able to act from outside. Oxygen availability in machinery spaces, dry cargo holds, accommodation, and tanker pump-rooms near ventilation fans heightens fire risk.
- Fire Main System for Cargo Ships: usually discharges seawater to suffocate Class A and B fires. Consists of a main pipeline extending to all parts of the ship along with pumps, valves, flexible hoses, and nozzles
It also includes an independently-powered emergency pump located away from machinery-space. The nozzles discharge in jet and spray modes
- CO2 System: employs a battery of cylinders working with smoke detection-alarm systems to protect machinery-spaces and cargo-holds. Regulations dictate the release of 85% of the total CO2 within two minutes. CO2 spreads throughout the compartment and cuts down relative oxygen content
CO2 Total Flooding System
- Automatic Water-Spray and Water-Mist System: spray system sprinkles water over large areas on fires in machinery and accommodation areas. It initially uses pressurized freshwater that does not corrode the tank. Pumps supply seawater when pressure drops
Mist/Fog systems discharge minute water particles that absorb heat and evaporate to provide cooling effect. The vapor so formed displaces oxygen. The dual effect soaks the fire rapidly using less water
- Inert Gas System: uses exhaust gas containing nitrogen and CO2 to suffocate fires
- Automatic Foam-Induction System: is a customize-able mechanism that normally uses mechanical foam. Mixing foam and water forms an agitating, fire-dousing mixture
- Halon System: is similar to CO2 The 1989 Montreal Protocol banned halon, an ozone depleting substance
Vigilance often prevents small challenges from metamorphosing into gigantic ones. Things are not very different while battling onboard fires.
For a comprehensive roundup of onboard challenges sailors face, visit our blog. To avail stellar marine fabrication services, marine pipe fitting, and large scale custom metal fabrication, contact Kemplon Engineering.