In redox processes, the reductant transfers electrons to the oxidant. Nitrogen is not considered to be a combustible substance when oxygen is the oxidant. Chemically, sulfur can react as either an oxidant or a reducing agent. Again sodium hypochlorite serves as the oxidant. Nitrogen dioxide is formed in most combustion processes using air as the oxidant. The preferred oxidant in industry is oxygen or air. Hydrogen is prevented from forming a passivating layer on the surface by the oxidant additive. A specialized use of manganese dioxide is as oxidant in organic synthesis. Acetic acid is the solvent and compressed air serves as the oxidant. Ammonium nitrate reacts with combustible and reducing materials as it is a strong oxidant. Chlorine is a strong oxidant that rapidly kills many harmful micro-organisms. NOCl behaves as an electrophile and an oxidant in most of its reactions. Fires can be extinguished by water, fuel or oxidant removal, or chemical flame inhibition. For example, the hydroxyl is a powerful, non-selective oxidant. HOCl is a stronger oxidant than chlorine under standard conditions.