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FOAM
SYSTEMS
 Types
of Foam
Chemical Foam
When two or more chemicals are added the foam generates due
to chemical reaction. The most common ingredients used for
chemical foam are sodium bicarbonate and aluminium sulphate
with stabilizer. The chemical foam is generally used in Fire
extinguishers.
Mechanical
Foam
It is produced by mechanically mixing a gas or air to a solution
of foam compound (concentrate) in water. Various types of
foam concentrates are used for generating foam, depending
on the requirement & suitability. Each concentrate has its
own advantage and limitations.
Low
Expansion Foam
For combating large hydrocarbon fires particularly in a contained
area like storage tank, foam has proved useful for its inherent
blanketing ability, best resistance and security against burn-back.
Aqueous Film Forming Foam (AFFF) compound is technically superior
and compatible with other fire fighting agents.
Efficient
and effective foam delivery system is a vital tool for its
usefulness in controlling the fire.
The
process of adding or injecting the foam to water is called
proportioning. The mixture of water & foam compound (foam
solution) is then mixed with air in a foam maker for onward
transmission to burning surface.
Conveying
Systems
The
system consists of an adequate water supply, supply of foam
concentrate, suitable proportioning equipment, a proper
piping system, foam makers and discharge devices designed
to adequately distribute the foam over the hazard.
Conventional
systems are of the open outlet type in which foam discharges
from all outlets at the same time, covering the entire hazard
within the confines of the system. There are three types
of systems :
i) Fixed
ii) Semi Fixed
iii) Mobile
Fixed
Foam System
Fixed
foam conveying system comprises of fixed piping for water
supply at adequate pressure, foam concentrate tank, inductor,
suitable proportioning equipment for drawing foam concentrate
and making foam solution, fixed piping system for onward conveying
to foam makers for making foam, vapour seal box and foam pourer,
suitable detection system may be provided to activate the
foam system.
Semi
Fixed Foam System
Semi fixed foam system gets supply of foam solution through
the mobile foam tender. A fixed piping system connected to
foam makers cum vapour seal box in case of cone roof tanks
and foam maker and foam pourers in the case of floating tanks
conveys foam to the surface of tank.
Mobile
Foam System
Mobile system includes foam producing unit mounted on wheels
which may be self propelled or towed by a vehicle. These units
supply foam through monitors/foam towers to the burning surface.
However,
certain other foam systems as follow are also available :
Sub
Surface Foam Injection : This is a system for protection of fixed roof storage tanks.
This comprises of high back pressure foam generator and connected
through product lines or separate lines near the bottom of
the tank.
Under
the Seal Foam Application : This is a system for floating roof tank where the foam travels
through a flexible pipe inside the tank up to the center of
the tank roof and exits at the seal rim of the floating roof
precisely where the fire is located thus rapidly flooding
the seal rim area and quickly extinguishing the fire.
Automatic
Actuated Foam Flooding System : In this system all the components and ingredients including
premix solution are contained within the system. Such systems
usually have a premix solution supply tank pressurized by
air or inert gas. The automatic sensing of fire releases this
pressure and places the system into operation.
Floating
Roof Tank Protection : For floating roof tank, foam shall be poured at the foam dam
to blanket the roof seal. Features of foam system for floating
roof tank protection shall be as follows:
- System be designed to create foam blanket on the burning surface
in a reasonably short period.
- Foam shall be applied to the burning hazard continuously at
a rate high enough to overcome the destructive effects of
radiant heat.
- Foam makers / foam pourers shall be located not more than
24 mtrs. apart on the shell perimeter based on 600 mm foam
dam height.
- A minimum of two pourers shall be provided.
Fixed
Roof Tank Protection
Foam conveying system shall have same features as of floating
roof tank excepting that a vapour seal chamber is required
before the foam discharge outlet.
Features
of the foam system for fixed roof protection shall be as
follows :
The vapour seal chamber shall be provided with an effective
and durable seal, fragile under low pressure, to prevent
entrance of vapour into the foam conveying piping system.
Where two or more pourers are required this shall be equally
spaced at the periphery of the tank & each discharge outlet
shall be sized to deliver foam at approximately the same
rate. Tank should be provided with foam discharge outlets
/ pourers depending upon the dia. of the tank.
Floating
cum Fixed Roof Tank Protection
Protection facilities shall be provided as required for fixed
roof tank.
Protection
for Dyke Area/Spill Fire
Portable
monitors/foam hose streams shall be considered for fighting
fires in dyke area and spills.
Water
for Foam Making
Water
quantity required for making foam solution depends upon the
type for foam used. Protein foams is normal use have a 3%
to 6% proportioning ratio. However, foam supplier data shall
be used for determining water quantity required.
Foam
System Components
- Inductors
- Foam makers
- Foam pourers
- Foam Tanks
- Foam Compounds
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