Foam-Water Sprinkler Systems for Fire Protection

How Does a Foam-Water Sprinkler System Work?

Foam suppression systems generally work by mixing foam concentrate into the water flowing through the pipe network. These systems are fitted with a bladder tank holding the foam concentrate. Once a fire is detected, a signal goes to the suppression panel, which opens the alarm valve and starts the water flowing. At the same time, piping to the foam tank applies pressure to the outside of the bladder, pushing the foam concentrate into the system piping and on to the foam proportioner. The foam solution produced by mixing water and foam concentrate flows through the system piping and discharges through open nozzles or sprinklers.

A foam-water spray system can be set up to discharge water first, then foam for a pre-set period, and then water again until the system is shut down manually.

Types of Foam-Water Sprinkler System

Foam suppression systems generally fall into four categories:

– Wet-pipe systems

– Dry-pipe systems

– Deluge-valve systems

– Preaction-valve systems

Definitions

Wet-pipe sprinkler systems: A sprinkler system using automatic sprinklers or nozzles connected to a piping network that is already charged with water.

Dry-pipe sprinkler systems: A sprinkler system using automatic sprinklers or nozzles connected to a piping network charged with pressurised air or nitrogen; once activated, it lets water pressure open the alarm valve.

Deluge sprinkler systems: A sprinkler system similar to a wet-pipe spray system, except that it uses open nozzle/sprinkler devices.

Preaction sprinkler systems: A sprinkler system similar to a dry-pipe system, with an additional detection system installed over the same area as the sprinklers. Preaction systems are typically used where damage from an accidental sprinkler discharge needs to be prevented. They generally fall into two groups: single-interlock preaction systems and double-interlock preaction systems. A double-interlock system needs two independent events to activate: first, the sprinkler piping loses its air or nitrogen pressure because one or more sprinklers has operated, and second, a solenoid valve is triggered by a fire detection device.

Types of Foam Concentrate

Several types of foam concentrate are available, matched to the application in question. The typical types of foam concentrate are:

– Aqueous film-forming foam concentrate (AFFF).

– Film-forming fluoroprotein foam concentrate (FFFP).

– Alcohol-resistant foam concentrate (AR-AFFF), typically used against fires in materials that would degrade standard AFFF or FFFP foam, as well as against hydrocarbon fires.

– Fluorine-free foam concentrate (SFFF).

As a general rule, foam concentrates of different types and/or brands should not be mixed with one another.