Fire fighting foams
Research: Environmental compatibility of foam extinguishing agents
The history of fire fighting foams dates back to the 19th Century
W
ith the oil production beginning in the 60s of the 19th Century and the increasing industrialisation, the requirements for a modern and safe extinguishing agent changed. In view of the particular dangers posed by flammable liquids, at the turn of the century (1900) the patent of the British researcher JH Johnsen, which had not yet been exploited, was reconsidered. As early as 1877, Johnsen had recommended a chemical foam produced by mixing two solutions, sodium bicarbonate, saponin and acidic aluminium sulphate, to combat the ‘fashionable’ petroleum fires. In 1914, the Austrian engineers I Stanzing and R König came up with the idea of producing extinguishing foam with the aid of a powder mixture to be added to the flowing water. Although this ‘dry system’ made fire fighting considerably easier, it proved to be very expensive. In the early 1920s, in the search for new basic materials for the production of extinguishing foam, water-soluble protein products were discovered, which were obtained by chemical digestion from organic raw materials such as hoof or horn. Only 8 | FIRE AND RESCUE INTERNATIONAL
in the mid-1930s was it possible to stabilise these protein products in such a way that a stable ‘air foam’ could be produced. It very quickly became apparent that this protein foaming agent was clearly superior to the chemical foaming agents known until then. This was the birth of modern air foam. Mixed into the flowing water stream in small doses, it can be used to produce a low expansion foam with high extinguishing intensity. In the course of the 1950s, the first synthetic multi-grade foams based on active washing substances became increasingly important. In 1953, this
included a patent for the first alcoholresistant, gel film-forming foam extinguishing agent. The use of PFC (poly fluorinated and per fluorinated surfactants) in foam extinguishing agents began in the early 1970s when the US Navy commissioned 3M to develop a particularly effective extinguishing agent for ships and aircraft carriers. In the 1980s and 1990s, the combination of alcoholresistant foam extinguishing agents with AFFF foaming agents resulted in the development of alcohol-resistant AFFF foaming agents suitable for universal use. The water film forming protein foaming agent ‘FFFP’ was also developed during this time. Foam extinguishing agents Foam extinguishing agents contain components such as glycols and glycol derivatives, surface-active substances (hydrocarbon surfactants for synthetic, protein hydrolysate for protein foaming agents) and foam stabilisers, as well as other components such as PFC, inorganic salts or polymer film formers. The environmental properties of foam extinguishing agents can be divided into three areas: • The toxicity of the products to aquatic organisms • The biodegradability and thus the duration of the retention in the environment • The effect of products on people
Figure 1: Types of fire fighting foam and their classification into PFC-containing and PFC-free Volume 5 | No 3
