Carbon dioxide extinguishant
Figure 1 Carbon dioxide properties Pressure Log. p Atomos. 4
quid
Solid li
3
Solid region
Liquid region
2
Liqui
Cr. Pt.
d oole Triple point
er c Und
0 –1 –2
our
d vap
1
id
l So
ur
o ap
v
Vapour region
–3 –140 –120 –100 –80 –60 –40 –20 0 20 Temperature ºC
Local application of carbon dioxide fire extinguishant.
42 | Fire Australia
Spring 2013
40
60
80 100
not until the growth of the telephone system in the US that attention became focused on the special fitness of carbon dioxide for certain types of fire extinction. In 1914, the Bell Telephone Company of Pennsylvania recognised the desirability of avoiding damage to wiring by extinguishing agents and installed sevenpound capacity hand extinguishers. In the decade following the Great War, it was recognised that either syphon tubes were necessary as proposed earlier by Camus, or the carbon dioxide cylinders needed to be inverted as described by Luhmann, in order to conduct liquid rather than gaseous carbon dioxide from cylinders. Some sizeable installations followed; for example, the boiler room of the original RMS Queen Mary was protected by a battery of cylinders containing 1.5 tonnes of carbon dioxide. Right through World War II, carbon dioxide fire extinguishing systems performed yeoman service in the US in light marine, diesel–electric locomotive and intercity bus protection. During and after the war it was installed on patrol boats and on aircraft fire and rescue trucks.
In the early 1930s, the first carbon dioxide fire extinguishing system was installed on a single-engine US Navy aeroplane. It proved successful and was considered an early step towards realistic protection of aircraft in flight. DC-2, DC-3, DC-4 and DC-6 aircraft were equipped with carbon dioxide extinguishing systems. With the increased airflows necessary to cool larger radial engines, it became necessary to develop high-rate discharge carbon dioxide container valves and directional (selector) valves. Lockheed Constellations and some Super Constellations were provided with standard carbon dioxide systems for engine fires, fires in cabin heaters and fires in auxiliary power units. On later model Super Constellations, jet and turboprop aircraft, the weight penalty associated with carbon dioxide resulted in phase-out in favour of methyl bromide (De Havilland Comet 4), bromotrifluoromethane and dibromodifluoromethane. As a further illustration of the ubiquity of this gas, it is worth noting that chemical foam and soda–acid extinguishers used chemically liberated carbon dioxide as the expellant. A typical reaction applicable to chemical foam is: AI2SO4 + 6NaHCO3 → 2AI(OH)3 + 3Na2SO4 + 6CO2 aluminium sulphate + sodium bicarbonate > aluminium hydroxide + sodium sulphate + carbon dioxide Similarly, the acid–alkali reaction in soda–acid extinguishers generated sodium sulphate and, you guessed it, carbon dioxide. Even today, a significant proportion of the world extinguisher production uses carbon dioxide cartridges for agent expulsion. Carbon dioxide is also an important component of one popular inert gas fire extinguishing system.
Characteristics of carbon dioxide
Carbon dioxide is a relatively inert, colourless, odourless and tasteless gas that is approximately