Criteria for fire extinguishing foams

Combustion resistance

expresses the stability of the foam against the effects of flames and heat radiation.

Ageing characteristics

are assessed according to how long the water/foam concentrate mixture contained in the foam is retained or how slowly/quickly the foam dries out. The measuring unit for this is the water drainage time. STHAMEX-AFFF, for example, has a short water drainage time so that the aqueous film is formed instantly. FOAMOUSSE has a long water drainage time and is thus particularly adhesive.

Film forming

A differentiation is made between:

Polymer film
Aqueous film

Flowing characteristics

The ability of the foam to distribute it self rapidly over the surface of the fire. Good flowing characteristics ensure a quick fire fighting success.

Gas tightness

of the foam is necessary to suppress the discharge of flammable gases from liquids already extinguished or covered with foam as a precautionary measure. A gas tight foam prevents re-ignition and reduces the fire risk.


of the foam is required to apply its cooling, insulating and wetting properties to vertical surfaces and bulky incendiary matter.

The fire performance

of a foam is very much dependent on the afore mentioned criteria. For its determination fire tests are carried out in accordance with valid standards (e.g. DIN EN 1568). Test methods for the chemical and physical properties of foam concentrates are subject to the test standard applied.

Compatibility of foams upon use

Foams generated from different foam concentrates can be used simultaneously during a fire fighting operation. However, attention must be paid that alcohol resistant foams are used when extinguishing polar solvents.

Powder compatibility

STHAMER-fire extinguishing foams are suitable for combined use with foam compatible fire extinguishing powder.

Seawater resistance

is a requirement for using the foam on sea-going ships, in seaports or in the off-shore sector and is met by all STHAMER products. Even treated industrial water and river/brackish water do not have a negative influence on the foam or its fire-extinguishing properties.

Foaming (expansion)

indicates the ratio of the amount of water/foam concentrate mixture used to the amount of foam generated from it. If, for example, 10 litres of foam are produced from 1 litre of water/foam concentrate mixture, then the foam expansion rate is 1:10.

The foaming expansion depend on

the type and quality of the foam concentrate
the foam equipment used
the amount of foam concentrate used (induction rate)
the water pressure available

Water drainage time

specifies the time span after which e.g. 25 % or 50 % of the water/foam concentrate mixture contained in the foam is drained.

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