Gaseous Fire Extinguishing Systems - IG 100 Extinguishing Systems
2004 Edition

According to IS 15525 (Clause 4.4 and Table 2), IG 100 gas must have a minimum purity of 99.6% by volume. Moisture content should not exceed 50 parts per million by mass, oxygen concentration must be below 0.1% by volume, and other contaminants such as hydrocarbons, carbon monoxide, nitrogen oxides, and carbon dioxide should generally be under 20 parts per million by mass. These stringent requirements ensure the inert gas is clean and effective for fire suppression applications.

The minimum design concentration for IG 100 is established based on the type of fire hazard. For Class A fires (solid combustibles), the extinguishing concentration is increased by a 20% safety margin, with a minimum injected concentration of approximately 40% by volume, ensuring residual oxygen remains at or below 14%. For Class B fires (flammable liquids/gases), the Cup Burner test concentration is augmented by 30%. These values are calculated using formulas from the standard considering enclosure volume and leakage, ensuring effective oxygen reduction to prevent combustion and maintaining concentration until the temperature falls below the ignition threshold.

Safety protocols per IS 15525 include limiting design concentrations to not exceed 52% in occupied areas, with higher concentrations permitted only in unoccupied spaces. Below the No Observed Adverse Effect Level (NOAEL) of 43% IG 100, an inhibit switch and time delay are mandatory without egress restrictions. Between NOAEL and the Lowest Observed Adverse Effect Level (LOAEL) of 52%, additional requirements such as a maximum 30-second egress time and safety interlocks apply. Exposure limits restrict occupant presence based on concentration, with maximum allowable exposure times decreasing as concentration rises. Enclosure strength must comply with specified maximum pressure tolerances based on construction type.

Storage cylinders must be seamless and comply with IS 7285, certified by the Chief Controller of Explosives, designed to withstand maximum pressures calculated at 55°C or the highest controlled temperature. Cylinders require accurate pressure gauges and temperature-pressure charts. Piping systems should be designed to handle pressures of 20 MPa or 25 MPa at 55°C, depending on system class, using galvanized carbon steel or stainless steel pipes and fittings conforming to IS 15493. These provisions ensure system integrity, safety, and regulatory compliance.

Commissioning should follow IS 15493 guidelines, with the installation agency issuing a test certificate upon completion. Full-scale discharge testing is generally discouraged but may be conducted if required by authorities according to Clause 14. Alternative performance verification methods may be used when full discharge testing is not performed. Systems must meet accuracy limits for agent weight discharged (-5% to +10%) and discharge timing (±5 seconds). Any deviations require remedial actions and retesting to ensure compliance and reliable operation.