The standard specifies the criteria for designing, installing, and maintaining gaseous fire suppression systems that utilize HFC 227ea (Hepta Fluoro Propane) as the extinguishing agent. It targets professionals involved in fire safety within enclosed environments, ensuring effective control of Class A and B fires while maintaining human safety limits and system efficacy.
Overview
The standard specifies the criteria for designing, installing, and maintaining gaseous fire suppression systems that utilize HFC 227ea (Hepta Fluoro Propane) as the extinguishing agent. It targets professionals involved in fire safety within enclosed environments, ensuring effective control of Class A and B fires while maintaining human safety limits and system efficacy.
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Frequently Asked
According to IS 15517, the HFC 227ea gas must meet strict purity and quality criteria: a minimum purity of 99.6% by mass, moisture content not exceeding 10 ppm, acidity below 3 ppm, non-volatile residues limited to 0.01% by mass, and no visible suspended matter or sediment. These parameters are verified using gas chromatographic methods to ensure performance and safety.
The minimum design concentration is calculated by applying safety factors to the extinguishing concentration values determined experimentally. For Class B fuels (flammable liquids and gases), a 30% safety margin is applied, while Class A fires use a 20% factor. The concentration must never be below 7.5% by volume. When multiple fuels are present, the highest required concentration is adopted, and altitude corrections are applied using atmospheric correction factors.
IS 15517 advises that concentrations exceeding the Lowest Observed Adverse Effect Level (10.5%) should only be present in areas not normally occupied by people. Personnel exposure to lower concentrations (below the No Observed Adverse Effect Level of 9%) is considered safe. Additional precautions include avoiding direct skin contact to prevent cold burns from vaporizing liquid, ensuring adequate ventilation, uniform gas distribution to prevent pockets of high concentration, and employing inhibit switches and time delays to prevent accidental discharge.
The total amount of HFC 227ea needed is determined by multiplying the net enclosure volume by the design concentration and a temperature-dependent specific volume factor. The formula used is M = S × V × C / (100 - C), where S adjusts for temperature, V is net enclosure volume after subtracting volumes occupied by structural and occupancy-related objects, and C is the design concentration. The greater value from this calculation or tabulated data from the standard's tables is selected to ensure adequate agent supply.
Nozzle placement must ensure uniform concentration throughout the enclosure without causing disturbance such as splashing flammable liquids or dispersing dust. Nozzles are typically installed at a maximum height of 3.5 meters, with spacing not exceeding 6 meters and walls or partitions not more than 3 meters away from the nearest nozzle. Suspended ceilings and raised floors require nozzles within voids for simultaneous release. Piping design must account for the two-phase flow of liquid and vapor, pressure drops causing vaporization, and maintain appropriate flow velocities to deliver the agent effectively.
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