Page 116 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

loss, provides some cooling of the fuel surface by the absorption of heat,
isolates the fuel surface from the oxygen supply, and separates the
---ใช้เพื่อการศึกษาเท่านั้น---
flammable vapour layer from other ignition sources (e.g. flames or
extremely hot metal surfaces), thereby eliminating combustion. A good
foam blanket will resist disruption due to wind and draught, or heat and
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
flame impingement, and will reseal when its surface is broken or
disturbed. Foam is an electrical conductor and should not be applied to
energised electrical equipment.

There are several different types of foam concentrate available. These
include standard protein foam, fluoro-protein foams and synthetic
concentrates. The synthetics are divided into Aqueous Film Forming
Foam (AFFF) for normal use, and hydrocarbon surfactant-type foam
concentrates for use with alcohols and fuels blended with significant
quantities of alcohol. Normally, the protein, fluoro-protein and AFFF
concentrates are used at 3-6% by volume concentration in water. The
hydrocarbon surfactant type concentrates are available for use at 1-6%
by volume concentrations.

High expansion foam, made from hydrocarbon surfactant concentrates, is
available, with expansion ratios from about 200:1 to 1,000:1. A foam
generator, which may be fixed or mobile, sprays foam solution onto a fine
mesh net through which air is driven by a fan. High expansion foam has
limited uses. It is most often used to rapidly fill an enclosed space to
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extinguish a fire by displacing free air in the compartment. High expansion
foam is generally unsuitable for use in outside locations as it cannot
readily be directed onto a hot unconfined spill fire and is quickly dispersed
in light winds.

High expansion foam systems are being enhanced with the introduction of
a new development called “Hot Foam”, which is now being increasingly
used on ships as a replacement for halon. Heated water and foam are
mixed to reduce possible damaging effects caused by rapid cooling.

Medium expansion foam has an expansion ratio from about 15:1 to 150:1.
It is made from the same concentrates as high expansion foam, but its
aeration does not require a fan. Portable applicators can be used to
deliver considerable quantities of foam onto spill fires, but their throw is
limited and the foam is liable to be dispersed in moderate winds.

Low expansion foam has an expansion ratio from about 3:1 to about 15:1.
It is made from protein-based or synthetic concentrates and can be
applied to spill or tank fires from fixed monitors or portable applicators.
Good throw is possible and the foam is resistant to wind.

Foam applicators should be directed away from liquid petroleum fires until
any water in the system has been flushed clear.

Foam should not come into contact with any electrical equipment.

The various foam concentrates are basically incompatible with each other
and should not be mixed in storage. However, some foams separately
generated with these concentrates are compatible when applied to a fire
in sequence or simultaneously. The majority of foam concentrates can be
used in conventional foam making devices suitable for producing protein
foams. The systems should be thoroughly flushed out and cleaned before
changing agents, as the synthetic concentrates may dislodge sediment
and block the proportioning equipment.

82 © ICS/OCIMF/IAPH 2006