Design and installation of fixed foam fire extinguishing system - Code of Practice, Part 1: Low expansion foam
1989 Edition

According to the code, compatible low expansion foam concentrates include: Protein foam concentrates (3% or 6%) known for stability and heat resistance but limited to semi-surface use; Fluoroprotein foam concentrates (6%) offering enhanced flow, self-sealing properties, and suitability for sub-surface systems; and Aqueous Film Forming Foam (AFFF) concentrates (6%) which provide rapid fire control by forming a protective film and are applicable for sub-surface usage. AFFF can be premixed and stored up to one year, unlike protein foams.

Foam discharge outlets should be positioned to provide complete and uniform coverage, with at least one outlet per 10 square meters of protected area. Outlets are to be evenly distributed around the tank's perimeter. Specific maximum spacing depends on the dam height and foam injection location: for foam above seals behind dams, spacing varies from 12 to 24 meters; for injection below the pantograph seal, up to 40 meters; and between tube seals and weather shields, a maximum of 18 meters. For sub-surface foam systems, multiple injection points are radially arranged from a central manifold delivering equal flow rates, and foam discharge must occur above any water layer inside the tank.

Recommended maintenance includes weekly visual inspections by system owners checking for leaks, damage, correct control settings, and verifying water supply and operator readiness; quarterly servicing of electrical detection and alarm components; semi-annual mechanical checks covering foam equipment, valves, pipework, and strainer cleaning; and annual testing of foam concentrate quality along with full-scale foam discharge tests. All inspections and maintenance activities should be documented, with owners retaining ultimate responsibility for system readiness.

Low expansion foam is unsuitable for running or flowing fuel fires, as it cannot effectively control moving fuels. It is also limited by temperature, being ineffective and potentially hazardous above approximately 100°C due to steam-induced frothing and overflow. Water-miscible flammable liquids require specialized stabilized foams rather than standard formulations. The foam is ineffective on gas or cryogenic liquid fires and must not be used on reactive metals such as sodium and potassium, with caution advised for magnesium. Additionally, due to its conductivity, low expansion foam should not be applied on energized electrical equipment. Compatibility with other wetting agents is restricted, with AFFF preferred, and water jets should be avoided as they may disrupt the foam blanket.

Foam concentrate proportioning is achieved through several methods including premixing, where foam concentrate is combined with water before delivery; induction, where concentrate is drawn into the water stream via pressure differential using self-induction (inductor near nozzle), in-line induction (inductor in the pipework), bypass induction (water diverted to induce concentrate), or around-the-pump induction (inductor in pump bypass line). Displacement proportioners use a bladder system where water pressure forces concentrate into the water flow. Control of concentration is maintained by limiting concentrate container height (usually within 2 meters of induction point), utilizing metering valves, and ensuring inductors maintain stable concentrations despite pressure and flow variations within design parameters.