Fire Protection Specialist Changed CFPS Questions

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Explosions or fires from flammable gas or oil fuel vapor-air mixtures may be prevented by ventilation and controls that keep the flammable vapor content below 25% of the lower flammable limit (LFL) of the vapor-air mixture, according to the web search results. The LFL is the lowest concentration of a gas or vapor in air that can produce a flash of fire in the presence of an ignition source. Below the LFL, the mixture is too lean to burn. The LFL varies for different gases and vapors, and it is usually expressed as a percentage by volume of air at 25°C and atmospheric pressure. For example, the LFL of methane is 4.4%, which means that a mixture of methane and air with less than 4.4% methane cannot ignite. To prevent explosions or fires, the concentration of flammable gases or vapors should be kept below 25% of their LFL, which is equivalent to 1.1% methane in this case. Ventilation, natural or mechanical, is one of the methods to achieve this by diluting the flammable gases or vapors with fresh air.Controls, such as gas detectors, alarms, valves, and interlocks, are another method to monitor and regulate the flammable gas or vapor levels and prevent them from reaching dangerous concentrations1234

The duration of required fire flow in public supply systems depends on the type of occupancy, construction, and exposure of the building, as well as the availability and reliability of the water supply. According to NFPA 1, Fire Code, Table 18.4.5.1.2, the minimum duration of fire flow for most occupancies ranges from 1 to 4 hours, with some exceptions for high-rise buildings, health care facilities, and special hazards. The fire flow duration is intended to provide enough water for fire suppression and exposure protection until the fire is under control or extinguished.References: NFPA 1, Fire Code, 2023 Edition, Section 18.4.5.1.2 and Table 18.4.5.1.2; NFPA Fire Protection Handbook, 21st Edition, Chapter 9, Section 9.2.2.

Wet chemical extinguishing agents, such as potassium acetate and potassium citrate, when sprayed on a grease fire, extinguish the fire by smothering and cooling. The wet chemical agent reacts with the hot grease and forms a layer of soap-like foam on the surface of the fat, which acts as an insulation between the hot grease and the atmosphere, preventing the escape of combustible vapors and oxygen supply.The wet chemical agent also absorbs heat from the grease and lowers its temperature below the ignition point12

References:

• What is the Difference Between a Wet and Dry Chemical Fire …
• Wet Chemical (Class K) Fire Extinguisher - Portable - WFX