INERTING/PURGING MATERIALS
In principle, any noncombustible gas can be used for dilution purposes in inerting/purging operations. However, nitrogen, steam, carbon dioxide, and argon are the most commonly used materials. Occasionally, halogenated hydrocarbons, such as halon gas, are used for special applications.
Nitrogen
Nitrogen gas is the most widely used material for inerting/purging operations. It is inexpensive, widely available, not hazardous, environmentally benign, and not prone to condensing at atmospheric conditions. However, the minimum oxygen concentration for a fuel is typically lower with nitrogen as the diluent than with steam or carbon dioxide. As a result, the ISOC and the OSFC are lower for nitrogen than for steam or carbon dioxide.
Steam