Foam/water spray systems
Foam water spray systems can be used for a combination of Class A and Class B hazards. They are mostly applicable to the protection of two-dimensional flammable liquid hazards.
Method of operation for foam water spray systems
Foam water systems generally work by allowing foam concentrate to mix with water flowing into the piping system. These systems are equipped with a bladder tank containing foam. When a fire is detected a signal is sent to the releasing panel to open the deluge valve allowing water to flow. At the same time, piping to the bladder tank flows and pressurizes the outer shell of the bladder tank which forces foam concentrate to travel into the system piping and then into the Foam Proportioner. The foam solution produced by water and foam concentrate flows into the system piping and is discharged through the open nozzles or sprinklers
Foam water spray systems can be used for discharge of water first, followed by discharge of foam for a pre-determined period, and then followed by water until manually shut off.
Fig. 1 - Foam water/system basic layout
Types of foam water spray systems
Foam water systems are generally divided into the following four (4) categories:
- Wet pipe systems
- Dry pipe systems
- Deluge systems
- Pre-action systems
Wet pipe spray systems: A sprinkler system employing automatic sprinklers or nozzles that are connected with a piping system that contains water.
Dry pipe spray systems: A sprinkler system employing automatic sprinklers or nozzles that are connected with a piping system that contains air or nitrogen under pressure, the release of which permits the water pressure to open a valve.
Deluge spray systems: A sprinkler system similar to the wet pipe spray system, except for employing open discharge devices.
Preaction spray systems: A sprinkler system similar to the dry pipe spray system with the addition of a supplemental detection system installed in the same area as the sprinklers. Preaction systems are generally used in areas where damage from the inadvertent operation of water spray systems must be avoided. Preaction systems generally divide into two (2) groups: single interlock preaction systems and double interlock preaction systems. Double interlock preaction systems require two independent events to activate. Firstly, the sprinkler piping loses air or nitrogen pressure due to the operation of one or more sprinklers, and secondly, the solenoid valve is triggered by the operation of a fire detection device.
Types of foam concentrate
Various types of foam concentrate exist, following the application considered. Typical foam concentrate types are the following:
- Aqueous Film-Forming Foam Concentrate (AFFF).
- Film-Forming Fluoroprotein Foam Concentrate (FFFP).
- Alcohol-Resistant Foam Concentrate, used for fighting fires on materials usually destructive to regular AFFF or FFFP foams as well as fires involving hydrocarbons.
- Fluoroprotein Foam Concentrate.
- Synthetic Foam Concentrate.
In general, different types and/or brands of foam concentrates shall not be mixed together.