High Expansion Foam: Where It Fits in Industrial Fire Protection
High expansion foam is foam with an expansion ratio above 200:1, meaning one gallon of solution becomes more than 200 gallons of bubbles. In practice, many generators operate between 500:1 and 1,000:1. It has two main roles in industrial fire protection: total flooding of enclosed spaces and vapor control on LNG and other cryogenic spills. It is not a substitute for low expansion foam on open pool fires, performs poorly in wind and does not extinguish pressure-fed or three-dimensional fires.
What Makes High Expansion Foam Different?
NFPA 11 divides foam into three expansion bands. Low expansion foam is below 20:1 and produces the heavy blanket normally used on fuel surfaces. Medium expansion foam ranges from 20:1 to 200:1 and can provide greater foam depth for bunds and localized spill protection. High expansion foam is above 200:1 and uses a generator to produce a large volume of lightweight bubbles that can rapidly fill an enclosed space.
The main difference is the amount of air contained in the finished foam. A low expansion blanket contains considerably more water and is designed to cool and seal a fuel surface. High expansion foam contains much more air and comparatively little water, allowing a small quantity of solution to create a very large volume of foam. For example, 1,000 gallons of solution at an 800:1 expansion ratio can produce approximately 800,000 gallons of finished foam.
High Expansion Foam for Enclosed Spaces
The classic application is total flooding of an enclosed or semi-enclosed area where conventional sprinklers may not effectively reach the fire. Typical applications include warehouses, cable tunnels, generator rooms, pump rooms and aircraft hangars.
NFPA 11 provides design requirements based on the hazard, building construction and required submergence depth. The generators must produce enough foam to reach the required depth within the specified submergence time. Designs also account for factors such as foam breakdown, leakage through openings, heat and the volume occupied by equipment.
High expansion generators may be installed inside the protected space or arranged to draw air from outside. The appropriate configuration depends on the application and system design. The concentrate is also specifically formulated for high expansion applications and should not be assumed to be interchangeable with standard low expansion foam concentrates.
Aircraft Hangars and High Expansion Foam
Aircraft hangars are a significant application because of their large enclosed volumes and flammable-liquid hazards. NFPA 409 provides several fire protection arrangements for aircraft hangars, including foam-water systems and arrangements combining sprinklers with low-level foam systems.
High expansion foam can be considered where the applicable hangar design permits it, particularly when an owner is looking for alternatives to fluorinated foam systems. The final system selection depends on the hangar classification, aircraft operations, hazard assessment and applicable listing requirements.
High Expansion Foam for LNG Vapor Control
Another important application is LNG spill and vapor control. LNG rapidly vaporizes when released because it absorbs heat from its surroundings. A layer of high expansion foam can help reduce heat transfer to the liquid and slow vapor generation.
High expansion foam can also reduce radiant heat from an ignited LNG pool. Its role in this application is primarily vapor and heat control rather than simply extinguishing the fire.
Dry chemical can provide the complementary extinguishing function for fires involving transfer arms, pumps, flanges and other three-dimensional sources. This is why industrial LNG protection may combine foam-based vapor control with dry chemical suppression where the hazard assessment calls for both.
Planning fire protection for an industrial or LNG application? Request a quote or request system information from Salus Global.
Where High Expansion Foam Should Not Be Used
High expansion foam has clear physical limitations. It is lightweight and can be displaced by wind, making it unsuitable for many open-air applications. Open tank farms, loading racks and exposed process areas generally require a different foam approach based on the hazard and environmental conditions.
For an open hydrocarbon pool fire, low expansion foam provides a heavier blanket with better surface coverage, cooling and burnback resistance. Medium expansion foam may also be considered for certain localized applications.
High expansion foam also has little value against a pressure-fed or three-dimensional fire. A leaking flange, pressurized fuel release, pump seal fire or gas jet does not provide a stable surface for the foam to occupy. These hazards may require dry chemical suppression combined with isolation of the fuel source.
High Expansion Foam vs. Other Foam Types
| Application | Preferred Foam Approach | Primary Purpose |
|---|---|---|
| Storage tank surface | Low expansion | Fuel surface blanket and burnback protection |
| Dike or bund spill | Low or medium expansion | Surface coverage and vapor control |
| Loading rack or pump area | Low expansion with dry chemical | Pool protection plus three-dimensional fire knockdown |
| Warehouse or cable tunnel | High expansion | Rapid filling and total flooding |
| Generator or enclosed equipment room | High expansion | Volume filling and fire suppression |
| Aircraft hangar | High or low expansion with applicable systems | Large-volume fire protection |
| LNG impoundment | High expansion with dry chemical | Vapor and radiant heat control |
| Jet fire or spraying leak | Dry chemical | Rapid flame knockdown and source isolation |
High Expansion Foam vs. Low Expansion Foam
The choice is primarily determined by the physical characteristics of the hazard. Low expansion foam is heavier and is intended to remain on a fuel surface. High expansion foam creates enormous volumes quickly and is therefore better suited to enclosed spaces where the objective is to fill the available volume.
For an open fuel pool, the heavier low expansion blanket is generally the better solution. For an enclosed room where equipment and obstructions make direct application difficult, high expansion foam can reach areas that conventional discharge devices may not cover effectively.
High Expansion Foam Maintenance
A high expansion system is only useful if the generators, concentrate and associated equipment remain ready for operation. Concentrate should be sampled and tested according to the applicable standard and manufacturer's requirements. Generators should also be inspected and tested to confirm that they can produce the required expansion characteristics.
Cold-weather installations require additional attention because water-based foam solutions and system components can be affected by freezing. Generator screens, piping, valves and other components should be maintained according to the system manufacturer's requirements.
Testing should confirm that the system continues to meet its listed performance requirements without unnecessarily flooding the protected building. The manufacturer's instructions and applicable NFPA requirements determine the appropriate inspection and testing procedure.
Frequently Asked Questions
What is high expansion foam?
High expansion foam is a fire-fighting foam with an expansion ratio above 200:1. It produces a very large volume of lightweight foam from a relatively small amount of solution and is primarily used for enclosed-space protection and selected vapor-control applications.
Can high expansion foam extinguish an open fuel fire?
It is generally not the preferred solution for an open-air fuel pool. Low expansion foam provides a heavier and more stable blanket for open hydrocarbon surfaces, while high expansion foam is more vulnerable to wind and has comparatively low water content.
Can high expansion foam be used for LNG?
High expansion foam can be used for LNG vapor and radiant heat control in appropriate applications. It should not automatically be treated as the sole extinguishing method. Dry chemical may be required for flame knockdown and protection of transfer equipment, depending on the hazard assessment.
Is high expansion foam fluorine-free?
Many modern high expansion concentrates are synthetic, fluorine-free products because film formation is not the primary mechanism of high expansion foam. The specific concentrate should always be checked against its product data sheet and listing.
How is a high expansion foam system tested?
Testing can evaluate generator operation, expansion ratio and drainage characteristics without necessarily flooding the entire protected building. The applicable NFPA requirements and manufacturer's instructions should be followed for inspection, testing and acceptance.
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