Anti-corrosive protection of the steel bodies of fire extinguishers has
always been one of the major problems confronting the manufacturers of fire
extinguishers.
Since the introduction of polythene as a lining rnaterial in about 1955,
there has been some controversy between manufacturers and others as to the ability
of polythene adequately to protect a steel body from the corrosive effects of
water and foam compounds, particularly if the extinguisher were under pressure.
Various suggestions of possible defects in this method of protection have been
made, including:-
(1) Poor adhesion of the polythene to the body, allowing moisture to become
trapped and start corrosion.
(2) Permeability under pressure of the polythene to water, causing corrosion,
(3) Air bubbles in the polythene which would expand and burst with an increase
in temperature.
In order that some assessment could be made of the efficiency of polythene'
as a lining, the opportunity was taken to examine twenty-four 2 gallon foam/gas
pressure polythene-lined extinguishers supplied by the Ministry of Works. The
extinguishers had been in use as containers to test the keeping qualities of
aqueous solutions of different proteinous foam compounds, when stored under a
pressure of 150 lb/sq.in for periods up to 2 years.
