We can extinguish a fire in many ways. Based on the site condition and hazard classification, a fire protection specialist decides which fire suppression or protection agent would work optimally. Most of the cases water-based fire protection systems work well. However, there are some scenarios where water does not give the best results but other agents such as foam, clean agent, dry or wet chemical agents do.
Foam is comprised of three ingredients named foam concentrate, water, and air. Foam solution consists mostly of water 94 to 97%. This makes foam suppression systems an effective option for protecting flammable and combustible liquids.
Standards to Follow
- NFPA 11: Standard for Low-, Medium-, and High-Expansion Foam
- NFPA 16: Standard for the Installation of Foam-Water Sprinkler and Foam-Water Spray Systems
- NFPA 24: Standard for the Installation of Private Fire Service Mains and Their Appurtenances
- NFPA 20: Standard for the Installation of Stationary Pumps for Fire Protection
- NFPA 25: Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems
Effects of applying foam on fire
- When generated in sufficient volume, they can prevent the air necessary for continued combustion from reaching the fire.
- When forced into the heat of a fire, the water in the foam is converted to steam, which reduces the oxygen concentration by diluting the air.
- The conversion of the water to steam absorbs heat from the burning fuel. Any hot object exposed to the foam will continue breaking down the foam, converting the water to steam, and being further cooled.
- Because of its relatively low surface tension, foam solution not converted to steam will tend to penetrate Class A materials. However, deep-seated fires may require an overhaul.
- When accumulated in-depth, high-expansion foam can provide an insulating barrier for the protection of exposed materials or structures not involved in a fire, thereby preventing fire spread.
How a foam-based fire protection system Works
Where a combustible or flammable liquid is stored in tanks or bulk storage facilities, foam is the best fire suppression agent of choice. It is very effective when the flammable liquid has a surface where the foam can be applied. Most flammable liquids or hydrocarbon fuels are lighter than water. So water will sink to the bottom and becomes ineffective. Otherwise, fire suppressing foam is lighter and will rise to the top. When foam concentrate, water, and air mixed correctly, they form a homogeneous foam blanket on the liquid fuel surface that extinguishes flames by the combined mechanisms of cooling, separating the flame source from the product surface, suppressing vapors, and effectively smothering the potential fire.
Types of Foam
- Low-expansion foams have an expansion rate less than 20 times. It can create a fire-suppressing film on a large surface area of a flammable liquid quickly.
- Medium-expansion foams have an expansion ratio of 20–100.
- High-expansion foams have an expansion ratio of over 200–1000 and are suitable for enclosed spaces such as tunnels, aircraft hangars where a quick filling is needed to smother the fire.
Most of the foam solutions are available in 1%, 3%, and 6% concentrates. This means it needs 99%, 97%, and 94% of water respectively to produce proper foaming along with sufficient air.
Commonly Used Foams
- Aqueous Film Forming Foams (AFFF)
- Film-Forming FluoroProtein (FFFP)
- Alcohol-Resistant Aqueous Film-Forming Foams (AR-AFFF)
AFFF is best for spills of liquid hydrocarbon fuels such as Octane, jet fuels, etc. FFFP is better for cases where the burning fuel can form deeper pools, and AR-AFFF is suitable for burning Alcohols.
Foam suppression systems should not be used in the following types of fire:
- Electrical fire: As foam contains more than 94% of water, so it is not recommended as a fire safety solution for live electrical equipment. There is a higher possibility of amplification of damage due to the conductivity of water.
- 3-dimensional fires: Foam works better in 2-dimensional spaces as it needs to cover the burning surface totally to suppress the fire. It is tough to cover a large 3-dimensional body with foam as it will fell down due to gravity. It gets worse if reignition occurs repeatedly.
- Pressurized gases: Gases are lighter than foam. So it will not work.
- Burning metals: Water in foam reacts viciously with active metals and produce heat and Hydrogen. And Hydrogen is also a fuel. So you know the consequence.
Foam-Based Fire Protection Equipment
- Bladder tank
- Foam concentrate pump
- Deluge valve
- Proportioner
- Foam Chamber
- Foam Monitor
- Concentrate control valve
- Foam sprinkler
- Detectors with Control panel
- Other control valves
Foam-Based Fire Protection Solutions
- Foam suppression system for Fuel storage tanks
- Foam Sprinkler System
- Compressed Air Foam System