HALON Halogen based vapourising liquids
General description • Halogenated hydrocarbon derived from such as methane and ethane – good extinguishing agents • Example: • Carbon tetrachloride (CTC) • 1.1.1 trichloroethane (methyl chloroform) • Bromomethane (CB) • Bromochlorodifluoromethane (BDF / 1211) • Bromotrifluoromethane (BTM / 1301) • All are toxic, decomposed when contact with fire – produced acid gas with chlorine, bromine or fluorine
General description (cont/..) • Due to this reason, authorities reluctant to accept • However, BCF & BTM less toxic, accept for marine use
Halon numbering system • 1st no – number of carbon atoms • 2nd no – number of fluorine atoms • 3rd no – number of chlorine atoms • 4th no – number of bromine atoms • 5th no – number of iodine atoms If only 4 numbers available such as 1301, meaning?
Effect of component gases • Bromine • Chain breaker • Bad for ozone • 1500x worst than fluorine • Fluorine – increase its inertness and stability • Bromine – increase its fire extinguishing effectiveness
Physical properties • Colourless & odourless gas • Non-corrosive in gas state, highly corrosive when dissolved in water • Used nitrogen for pressurised – 42 bar at 20°C • Process – disrupts the chain reaction of combustion - extinguish fires
Toxicity • Safest agent - comparing toxicity level • Concentrations up to: • 7% can breathed 5 minutes without effect • 10% reduced to 1 minute • Temperature above 510°C – halon will decompose • Important products – Hydrogen Bromide (HBr) & Hydrogen Fluoride (HF) • Small concentrations – cause irritant, give forewarn to personnel of increasing concentrations • Considered lesser threat than other products of fire poisonous smoke - carbon monoxide etc.
Required concentration • 4.25 to 5% by volume
Advantages • Clean with no residue • Only slightly toxic / irritant • Easy and safe to store • Electrically non-conductive • Good penetration • Suited to automatic release • Low working concentrations – relatively safe for personnel • Fast action / response / extinguish quickly • Smaller quantity than CO2 needed – enclosed spaces • Slightly pressurised storage container / keep low pressure in liquid form • Negative catalyst
Disadvantages • Toxic gas produced when contact with fire • Expensive • Limited world recharging facilities • Require propellant gas for quick release
Regulations • Only permitted machinery space, pump rooms or cargo spaces solely for carriage of vehicles not carrying cargo • No new installations • System designed – minimum medium quantity discharged to space based on liquid phase within 20s • Means of safely checking pressures
Regulations (cont/…) • Volume 0.16m³/Kg • Fire resistant release mechanism • Over pressure device fitted • Leakage warning alarm • For locally operated devices the concentration should not above 7% for 1301 and 5.5% for 1211 at 20°C • Discharge time for liquid phase < 10s
Montreal convention • Following the Montreal protocol, the usage of Halons was agreed to be: • halved by the year 1995 • phased out by the year 2000
Response / plan by IMO • No new installations after July 1992 • Testing of systems banned by January 1992, integrity test on spaces required • Requirement for Halon stocks to be recorded • Existing Halon systems phased out by 2000
2nd requirement – Halon should only used as fire fighting medium in space where no other suitable means of extinguishing the fire to protect personnel and property • This guideline is valid until January 2000 • Companies required to replace with suitable alternative - difficulty in restocking Halon as production of Halons is phased out by industry • Have suitable alternative method fitted at owners best interest. • To replace the system at convenience rather than as necessary • Halon systems still in use as of August 2000