How does high expansion foam differ from low expansion foam and which hazards are amenable for each type of system?
Originally, foam is one of the fire suppression means, and it is considered a better means, than water suppression. It creates better oxygen isolation, and it is lighter than water. These features make the foam more suitable for extinguishing burning fuels. High expansion foam is suitable for fire suppression in industrial premises, subject to immediate fire expansion. These are hangars, workshops, storages, etc. As for the technical side of high expansion foams, it is suitable for numerous applications including three-dimensional hazards, confined spaces, and vapor suppression. High expansion foams are less water consumptive, so these foams are less cooling. (Gagnon, p.35)
Low expansion foams are more water consumptive, consequently, they make a greater cooling effect that makes them suitable for high-temperature fires. Low expansion foams create more dense oxygen isolation and are suitable for localized effects (in the premises with fire isolation).
Describe the impact and influence of the EPA on foam system design
The fire suppression foams contain elements that are harmful to the environment. These are chlorides, which define the density of the foam, and the extent of oxygen isolation. These components may penetrate into soil and water, and cause contamination. Consequently, the key specification, set up by EPAs is the lessening of chloride presence in foams or using of chloride substitutes. The tanks and containers of foaming components should be produced of solid and light materials (steel, duraluminium), and be protected from leakages. (Gagnon, p.56)
Why are the required design densities for air-aspirated nozzles and non-air- aspirating nozzles different for aircraft hangars?
The designs of the nozzles, and the fire suppression systems that should be used in hangars generally depend on the sizes of a hangar, types of aircraft, and the type of fuel that is used and stored.
If air aspirated equipment is installed, the design discharge can be decreased from 0.20 gpm/sq.ft. (8.12Lpm/sq.m.) to a minimum of 0.16 gallons of foam per minute, per square feet (6.5 Lpm/sq.m.) of floor area. The use of automatic sprinkler devices and automatic low-level, low expansion foam equipment can also be helpful if this combination is added with the air-aspirating nozzle. (Gagnon, p.98)
The non-air-aspirating type provides a better stream and is featured with a constant flow whether on straight stream or fog patterns. Non-air-aspirating types of fire suppression systems are less energy-dependent and are more rapid in action. The differences in the construction of air-aspirated and non-air-aspirated nozzles are essential, and presuppose that air-aspirated modification requires air for proper effect, while close premises may be too gassed.
What advantage would floor drain mounted foam discharge devices have as opposed to WOM’s in an aircraft hangar?
Floor drain mounted foam discharge devices are more suitable for small premises, where there is no place for installing the reserve tank with water or components necessary for foaming. In spite of the fact that these systems are too dependent they do not require quarterly official checkups (in most US states) and recharge of chemical components. Consequently, these systems are safer for the environment. (Gagnon, p.145)
Works cited
Gagnon, Robert. Design of Special Hazard & Fire Alarm Systems Delmar Cengage Learning. 1997.