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