Water and Foam

  • Water and Foam Fire Extinguishers:
Water Extinguisher

Water Extinguisher

They extinguish the fire by taking away the heat element of the fire triangle (i.e by sudden cooling). Foam agents also separate the oxygen element from the other elements of the fire triangle (i.e fuel, heat and Chemical Reaction).

Water Extinguishers are for Class A fires only – they should not be used on Class B or Class C fires. The disharge stream could spread the flammable liquid in a Class B fire or could create a shock hazard on a Class C fire. Water cans are easily refilled by filling the cylinder with water about 3/4 of the way up. The top is then screwed back on and the unit is pressurized with an aircompressor. They contain 2.5 gallons of water or water with a wetting agent which is applied by means of a 1/2 inch hose with a smooth-bore nozzle attached to the tip. They produce a 40-50 foot stream of water, with a discharge time of about 45 seconds Although only effective on only Class A fires, they have the advantage of being inexpensive, harmless, and easily refilled as well as having the advantage causing no mess, resulting in easy clean-up.

Foam Extinguishers can be used on Class A & Class B fires only. They can’t be used on Class C because of Electrical Shock Hazard.

Class B fires can be controlled with foam extinguishers. Unlike
any other type of portable fire extinguisher, foam extinguishers can cover Class B spills with foam to help prevent ignition.
Foam extinguishers also have a number of disadvantages. For example, these units are only effective on class A and B fires and can be dangerous if used on class C or D fires. The extinguishers are relatively heavy. In any area that is not continuously heated, the unit is subject to freezing. Antifreeze can be added to prevent freezing, but that makes maintenance more difficult.

Fire Retardant Foam, or fire suppression foam, is a foam used for fire suppression. Its role is to cool the fire and to coat the fuel, preventing its contact with oxygen, resulting in suppression of the combustion. The surfactants used need to produce foam in concentration of less than 1%.

Other components of fire retardant foams are organic solvents (eg. trimethyltrimethylene glycol and hexylene glycol), foam stabilizers (e.g. lauryl alcohol), and corrosion inhibitors.

Low-expansion foams have an expansion rate less than 20 times. Foams with expansion ratio between 20-200 are medium expansion. Low-expansion foams such as AFFF are low-viscosity, mobile, and able to quickly cover large areas.

High-expansion foams have an expansion rate over 200. They are suitable for enclosed spaces such as hangars, where quick filling is needed.

Alcohol-resistant foams contain a polymer that forms a protective layer between the burning surface and the foam, preventing foam breakdown by alcohols in the burning fuel. Alcohol resistant foams should be used in fighting fires of fuels containing oxygenates, eg. MTBE, or fires of liquids based on or containing polar solvents.

Class A foams
A fire truck demonstrating Class A foam in a CAFS system

Used for Class A fires, including structure fires. Class A foams facilitate wetting of class A fuels, lowering the surface tension of the water and assisting saturation of them with water, aiding fire suppression and preventing reignition.

Class B foams

Class B foams are designed for class B fires – flammable liquids. The use of class A foam on a class B fire may yield unexpected results, as class A foams are not designed to contain the explosive vapors produced by flammable liquids. Class B foams have two major subtypes.

Synthetic foams

Synthetic foams are based on synthetic surfactants. Synthetic foams provide better flow, faster knockdown of flames, but limited post-fire security.
Aqueous film forming foams (AFFF) are water-based, frequently containing sodium alkyl sulfate, and/or perfluoro telomer as surfactants. They have the ability to spread over the surface of hydrocarbon-based liquids. Alcohol-resistant aqueous film forming foams (AR-AFFF) are foams resistant to the action of alcohols, able to form a protective film when they are present.

Protein foams

Protein foams contain natural proteins as the foaming agents. Unlike other synthetic foams, protein foams are bio-degradable. They flow and spread slower, but provide a foam blanket that is more heat resistant and more durable.

Protein foams include regular protein foam (P), fluoroprotein foam (FP), alcohol resistant fluoroprotein foam (AR-FP), film forming fluoroprotein (FFFP), and alcohol-resistant film forming fluoroprotein (AR-FFFP).

Protein Foam from non-animal sources is preferred because of the possible threats of biological contaminants like prions.

Every type of foam has its application. High-expansion foams are used when an enclosed space, such as a basement or hangar, needs to be quickly filled. Low-expansion foams are used on burning spills. AFFF is best for spills of jet fuels, FFFP is better for cases where the burning fuel can form deeper pools, AR-AFFFF is suitable for burning alcohols. The most flexibility is achieved by AR-AFFF or AR-FFFP. AR-AFFF must be used in areas where gasolines are blended with oxygenates, since the alcohols prevent the formation of the film between the FFFP foam and the gasoline, breaking down the foam, rendering the FFFP foam virtually useless.

Applied to fuel fires as either an aspirated (mixed & expanded with air in a branch pipe) or non aspirated form to form a frothy blanket or seal over the fuel, preventing oxygen reaching it. Unlike powder, foam can be used to progressively extinguish fires without flashback.

* AFFF (aqueous film forming foam), used on A and B fires and for vapor suppression. The most common type in portable extinguishers. It contains fluoro tensides [4] which can be accumulated in human body. The long-term effects of this on the human body and environment are unclear at this time.
* AR-AFFF (Alcohol-resistant aqueous film forming foams), used on fuel fires containing alcohol. Forms a membrane between the fuel and the foam preventing the alcohol from breaking down the foam blanket.
* FFFP (film forming fluoroprotein) contains naturally occurring proteins from animal by-products and synthetic film-forming agents to create a foam blanket that is more heat resistant then the strictly synthetic AFFF foams. FFFP works well on alcohol-based liquids and is used widely in motorsports.
* CAFS (compressed air foam system) Any APW style extinguisher that is charged with a foam solution and pressurized with compressed air. Generally used to extend a water supply in wildland operations. Used on class A fires and with very dry foam on class B for vapor suppression.
* Arctic Fire is a liquid fire extinguishing agent that emulsifies and cools heated materials quicker than water or ordinary foam. It is used extensively in the steel industry. Effective on classes A, B, and D.
* FireAde, a foaming agent that emulsifies burning liquids and renders them non-flammable. It is able to cool heated material and surfaces similar to CAFS. Used on A and B (said to be effective on some class D hazards, although not recommended due to the fact that fireade still contains amounts of water which will react with some metal fires).

Advertisements
%d bloggers like this: