Fire Prevention, Detection, and Suppression - Water and Gas Based

Although water-based foam is useful in some applications, the most common method is through a building sprinkler system. Water-based systems are generally safe for people and relatively inexpensive but can damage equipment and would cause additional damage if applied to other fire classes.

Common water-based system types include:

• Wet pipe is the most common with water existing in the pipes and a heat-activated sprinkler head that typically operates independently.
• Dry pipe is pressurized gas in pipes, and water is released after the first sprinkler head is activated with a slight delay in operation. Sprinkler heads operate independently. It's beneficial due to less danger of pipe leaks or freezing, and often used in open facilities such as a parking garage.
• Pre-action combines elements of wet and dry pipe actions. Fire sensors initiate pre-action charging of the water pipes that can then activate independently as in a wet pipe system. In other instances, the system may require both an independent fire sensor and one or more sprinklers to activate prior to water entering the system.
• Deluge is similar to pre-action operation but with open sprinkler heads. Once the overall system is activated by a heat or fire sensor, all sprinkler heads will be active simultaneously when the central valve is opened.
• Aqueous Firefighting Foam (AFFF) is a water-soluble foaming agent applied that penetrates the combustible material and makes (re)ignition more difficult.
• Non-conductive, nontoxic liquid suppressants such as Novec 1230 fire protection fluid by 3M, which can be used instead of water or AFFF for class A, B, and C fires in enclosed equipment spaces where people are usually present.

Gas-based systems come in a variety of forms, and are effective against Class A, B, and C fires.

Gas systems work differently depending on the particular chemical composition of the gas. Some inhibit the chemical reaction necessary for combustion, others reduce heat, but most reduce the level of oxygen in the room by supplanting the air with the chemical gas.

Regardless of the mechanism, gas-based systems require people in the enclosed area affected by the gas to evacuate, ensuring the doors are closed behind them.

Proper system design must take into account the size and ventilation of protected rooms and volume calculations for the gas.

If well implemented, most modern gas systems can be safe for human occupied spaces, but some risk of suffocation may still exist if not implemented correctly or if unusual conditions apply.

Gas system examples include:

• Hydrofluorocarbon
• Halon (older type, phased out of commercial usage in most jurisdictions)
• FM-200

A number of other technologies exist. In addition to the water-based foams, several other foam types can be used to address unique circumstances.

• Carbon Dioxide (CO2)
• Argonite
• Inergen

In addition, aerosol-based systems exist (for example, Aero-K), which inject an inert gas with small (10-150 microns) solid particles into the protected area. They are typically safe for human occupied areas.