Download - Service Delivery 3
Service Delivery 3
Foam
Aim
To provide students with information
to enable them to control and
extinguish fires using foam.
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.
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.
Isolation
Dilution
Interception.
Vapours
Foam blanket
How foam extinguishes fire
• Cooling of the fuel
• Dilution of the surrounding air with water vapour from evaporated foam.
Main properties
• Stability
• Expansion
• Burn back resistance
• Fluidity
• Contamination resistance
• Sealing and resealing
• Knockdown and extinction.
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.
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.
Differing foam expansions.
Low expansion foam
Up to 21 metres throw.
High expansion foam
Negligible throw.
Factors affecting finished foam
• Concentration to water ratio
• Expansion (air mixed with solution)
• Size of bubbles (HX).
Production of finished foam.
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;
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;
High expansion (HX) foam
• Basements
• Ships holds
• Machinery spaces
• Cable ducting.
Particularly suitable for dealing with fires involving;
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.
• 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.
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.
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;
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
Inline inductor
Non return valveHermaphrodite induction coupling
supplying foam compound
Improver
Female couplingBy pass valve
FilterMale
coupling
Nozzle
Water
Foam
Solution.
Foam solution
Foam solution
Air
Air
Air
Air
Air
Fan Fine mesh screen
Operating principles of HX generator
Flexible
ducting
Finished
Foam.
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.
THE END