Current affairs
with either a weak solution of sulphuric acid or aluminium sulphate. The chemical action generates not only four to five times the volume of foam, but also sufficient carbon dioxide gas to expel the contents of the cylinder.
FOCUS
Powder is effective, but not in a Grade 1 listed building Soda acid and foam
incendiary bombs. The interesting 1938 advertisement for Nuswift below shows a very low key approach to promoting fire equipment.
Of the commonly used agents, only carbon dioxide would not be appropriate in the modular systems presently available – this is due to the pressure under which the CO2 gas is stored.
Dry powder
Dry powder, most commonly mixtures of mono ammonium phosphate, sodium bicarbonate, potassium bicarbonate and urea, is also widely used in portables. There are a range of trade names, but powder extinguishers can be classed as either ‘ABC’ or ‘BC’ depending on the types of fires on which they are effective. Powder for firefighting has a long history (although a government committee dismissed its value in 1916!). Powder was ‘rediscovered’ in the 1920s in the US by the oil industry, for which a quick knockdown of small fires was critical. Multipurpose powder was developed in Europe in the 1950s and then refined for the US Navy in the 1960s. However, as is now well known, while highly effective in knocking down most small fires, powder is extremely messy and requires a significant clean up after discharge. In some cases, liquid fires can reignite
after being extinguished if there is sufficient heat around to ignore residual vapour. An early use of powder was to counter WWII
www.frmjournal.com NOVEMBER 2018 49
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