Military Specification

ETL 1110-3-481

31 Mar 97

boiling point solvents and water. The surfactants alter the

surface properties of water in such a way that a thin aqueous

film can spread on a hydrocarbon fuel even though the aqueous

film is more dense than the fuel.

Military Specification

3.1

Aqueous Film-Forming Foam (AFFF) concentrate used in DoD

facilities must be "MIL-SPEC" foam conforming to MIL-F-24385.

MIL-SPEC foam is recognized in the fire protection community for

its high level of fire extinguishment and burnback performance.

In addition to fire extinguishment and burnback requirements, the

MIL-F-24385 provides for important chemical and physical

properties not specified by other standards. "MIL-SPEC" AFFF

concentrate is the standard by which others are measured. Other

commercially available AFFF concentrates are simply not

comparable to those conforming to MIL-F-24385.

Dilution

3.2

AFFF foam solutions are produced by diluting AFFF concentrates

with water through the use of a proportioning device. The

dilution ratio for 3% type concentrate, the most commonly used,

is 33.3 to 1. Similarly, dilution ratios of 16.7 to 1 and 100 to

1 are used for 6% type and 1%, respectively. The concentration

of chemicals in the foam solution does not vary significantly

with the percentage type of AFFF. In other words, the chemical

content of a 1% concentrate is roughly six times that of a 6%

concentrate and three times that of a 3% concentrate.

Fluorochemical Surfactants

3.3

Fluorochemical surfactants are essential ingredients in AFFF

concentrate. No other known class of materials has the

capability of producing aqueous solutions of sufficiently low

surface tension to permit the formation of an aqueous film on

hydrocarbon fuels. This low surface tension allows the aqueous

film to spread over and seal the surface of the fuel,

extinguishing the flames and preventing the flammable liquids

from evaporating. No other type of surfactant can do this as

effectively as a fluorochemical surfactant. Fire fighting agents

containing fluorochemical surfactants can extinguish flammable

liquid fires more quickly using lesser amounts of agent than fire

fighting agents not containing fluorochemical surfactants. A

drawback to fluorochemical surfactants is that they can move with

water in aquatic systems and leach through soil. Whereas a

readily degradable compound will break down as it leaches through

soil, fluorochemical surfactants will not. If allowed to soak

A-4