The 25 per cent drainage times of fire-fighting foams have hitherto been
determined using a 1400 ml pan, 18.7 cm diam. x 5 cm deep (7 3/8 in x 2 in). This
method was shown to have a low level of reproducibility when testing foam from
a 5 l/min (1.1 gal/min) branchpipe. It was found that the sample size must be
related to the flow rate of the foam stream being tested, and to its uniformity.
Details of a new 6320 ml drainage pan, 20 cm diam. x 20 cm deep (7.9 in x 7.9 in)
are given, which is suitable for testing foam from a 5 l/min branchpipe. The
25 per cent drainage time was found to be independent of pan diameter but
changed with pan depth. Details of a new 1630 ml drainage pan, 10 cm diam. x
20 cm deep (3.9 in x 7.9 in) are given, which gives the same drainage time as the
6320 ml pan, and is suitable for testing foam from a laboratory generator at
0.75 l/min (0.1 gal/min). It is recommended that 25 per cent drainage times
should always be measured in a pan of this depth, to give comparable results
between laboratories.
