Inert Gas Selection
Nitrogen is commonly used as an inert gas as it will not react with most materials. Nitrogen may not be suitable in some instances, as in processing some metal dusts, with which it can react. Magnesium dust is such a material. Similarly, carbon dioxide and water vapor can serve as oxidizers in metal dust systems. Water vapor condensation in metal dust systems poses a special hazard in that its slow low-temperature oxidation of metal dusts yields hydrogen gas. Hydrogen formed this way may accumulate in bulk or simply reside as an adsorbed phase within a dust layer causing the dust to become susceptible to ignition. Argon is usually used in these cases.
Furnace flue gas is sometimes employed as an inerting gas. It usually contains less than 3 vol % oxygen.
Halogenated hydrocarbons are employed successfully as combustion inhibiting agents. Due to economic considerations these are usually employed in on-demand batch inerting applications. Examples of such applications are pump rooms handling petroleum products and aerosol fill rooms. The principal halogenated agent employed for this purpose has been bromotrifluoromethane, known commonly as Halon 1301. Due to adverse environmental impact (high reactivity with stratospheric ozone) Halon compounds are soon to be prohibited from production. Fluorinated compounds are now being considered as replacements where Halon 1301 was once used.