Service Delivery 3
description
Transcript of Service Delivery 3
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Service Delivery 3
Foam
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Aim
To provide students with information
to enable them to control and
extinguish fires using foam.
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Learning OutcomesAt the end of the session students will be able to:
• Describe the principal methods by which foam extinguishes a fire
• State the types of foam concentrate in use
• List the types of foam making equipment in use
• Identify the considerations when using foam making equipment.
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How foam extinguishes fire
• Formation of a sealing blanket over fuel surface which prevents vapour escaping
• Interception of radiant heat from the
flames, preventing it from reaching the
surface of the fuel and causing further
evaporation
• Isolation of fuel from oxygen in the air.
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Isolation
Dilution
Interception.
Vapours
Foam blanket
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How foam extinguishes fire
• Cooling of the fuel
• Dilution of the surrounding air with water vapour from evaporated foam.
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Main properties
• Stability
• Expansion
• Burn back resistance
• Fluidity
• Contamination resistance
• Sealing and resealing
• Knockdown and extinction.
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Performance can be affected
• Type and operation of foam making equipment
• Type of foam concentrate
• Type of fire and fuel involved
• Tactics of foam application
• Rate at which foam is applied
• Quality of water
• Length of pre-burn.
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Types of foam
• Alcoseal (LX) - 4 x 22.5 litre drums on appliances
• FP70 (LX) - 6 X 1000 litre cubes (bulk supply on Equipment Support Units)
• Expandol (HX) - for high expansion generators.
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Differing foam expansions.
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Low expansion foam
Up to 21 metres throw.
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High expansion foam
Negligible throw.
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Factors affecting finished foam
• Concentration to water ratio
• Expansion (air mixed with solution)
• Size of bubbles (HX).
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Production of finished foam.
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Low expansion foam
• Can be projected over fairly long distances
• Spreads fairly quickly
• Is capable of forming a stable and secure foam blanket.
This is the most widely used foam because;
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Method of application
• Applied gently to the surface of the burning fuel, or
• The wall of the fuel container.
To avoid ‘stirring’ the fuel, foam should be;
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High expansion (HX) foam
• Basements
• Ships holds
• Machinery spaces
• Cable ducting.
Particularly suitable for dealing with fires involving;
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Considerations when using HX foam
• Foam concentrate requirement
• Siting of HX units
• Level of injection
• Ventilation
• Maintaining the foam
• Entering the compartment
• Hazards in HX foam.
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• Loss of senses, vision, direction and hearing
• DSU`s, alarms and evacuation signals will be very difficult to hear
• Penetration of light is severely restricted
• Heat transmission is reduced
• Possibilities of pockets of trapped gas
• Unable to observe damage to structure and obstructions.
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Safety precautions when working in HX foam
• Breathing apparatus essential
• Communications to be used at all times
• Guidelines must always be used
• Only enter for rescue or urgent need
• Ensure the fire is extinguished before entering
• Back up agents to be standing by.
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Foam making equipment
• Generators for LX foam
• Foam making branches for LX foam
• Generators for HX foam.
The aspirating devices used to produce foam are divided into three basic categories;
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Low expansion (LX) foam making branch
Standard instantaneous coupling
Strainer
On/Off control valve
Upstream orifice plate
Downstream orifice plate
Air intake holes
Dispersal disc
Finished
foam.
Foam solution
Turbulence chamber
Foam making tube
Semi circular baffles
Outlet nozzle
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Inline inductor
Non return valveHermaphrodite induction coupling
supplying foam compound
Improver
Female couplingBy pass valve
FilterMale
coupling
Nozzle
Water
Foam
Solution.
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Foam solution
Foam solution
Air
Air
Air
Air
Air
Fan Fine mesh screen
Operating principles of HX generator
Flexible
ducting
Finished
Foam.
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ConfirmationAssessments will be based on this lesson and the corresponding study note
Learning Outcomes• Describe the principal methods by which foam
extinguishes a fire
• State the types of foam concentrate in use
• List the types of foam making equipment in use
• Identify the considerations when using foam making equipment.
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THE END