An inert gas mixture containing 50% Nitrogen and 50% Argon by volume, used for fire suppression by oxygen displacement (Clause 4.1).

What is the minimum design concentration for a server room (Class A)?

37.5% for surface fires, which provides a safety margin over the 31.25% extinguishing concentration (Table 2).

Is IG-55 safe for people?

It is safe to use in normally occupied spaces up to its No Observable Adverse Effect Level (NOAEL) of 43%. Systems designed above this level require strict controls to ensure evacuation before discharge (Clause 4.3.3).

What is the maximum discharge time?

For Class A hazards, 95% of the design agent quantity must be discharged within 60 seconds (Clause 5.4.1.2).

IS 15506

: 2004

Gaseous Fire Extinguishing Systems - IG 55 Extinguishing Systems

CurrentSpecializedSpecificationBIMFire Safety · Fire Fighting

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This standard specifies requirements for the design, installation, testing, and maintenance of gaseous fire extinguishing systems using IG-55 agent. IG-55 is an environmentally safe inert gas blend (50% Nitrogen, 50% Argon) that extinguishes fire by reducing oxygen concentration. It is intended for protecting high-value assets and sensitive electronics where water-based suppression is undesirable.

Gaseous Fire Extinguishing Systems - IG 55 Extinguishing Systems

Quick Reference Values

Composition of IG-5550% Nitrogen, 50% Argon (by volume)

Minimum design concentration for Class A surface fires37.5%

Maximum discharge time for Class A fires (95% of agent)60 seconds

No Observable Adverse Effect Level (NOAEL)43%

Lowest Observable Adverse Effect Level (LOAEL)52%

Standard cylinder storage pressures200 bar or 300 bar

Key Formulas

X = 2.303 * (Vs/V) * log10(100 / (100 - C)) — Volume of agent per unit volume of hazard space

Practical Notes

Enclosure integrity is the single most critical factor for system success. A Door Fan Test (Annex G) is essential to quantify leakage and ensure the concentration is held for the required duration.

Hydraulic calculations for pipe and nozzle sizing are mandatory and must be performed with specialized software, as simple tables are insufficient for these complex systems.

Proper safety precautions, including time delays, pre-discharge alarms, and visible warning signs, are crucial for life safety in potentially occupied spaces.