This document specifies minimum requirements and defines the specifications governing the design, installation and maintenance of fixed oxygen reduction systems with oxygen reduced air for fire prevention in buildings and industrial production plants. It also applies to the extension and modification of existing systems. This document applies to oxygen reduction systems using nitrogen-enriched-air which are designed for continual oxygen reduction in enclosed spaces. NOTE Nitrogen is, today, the most suitable gas to be used for oxygen reduction. For other gases, this document can be used as a reference. This document does not apply to: — oxygen reduction systems that use water mist or combustion gases; — explosion suppression systems; — explosion prevention systems, in case of chemicals or materials containing their own supply of oxygen, such as cellulose nitrate; — fire extinguishing systems using gaseous extinguishing agents; — inertization of portable containers; — systems in which oxygen levels are reduced for reasons other than fire prevention (e.g. steel processing in the presence of inert gas to avoid the formation of oxide film); — inerting required during repair work on systems or equipment (e.g. welding) in order to eliminate the risk of fire or explosion. In addition to the conditions for the actual oxygen reduction system and its individual components, this document also covers certain structural specifications for the protected area. The space protected by an oxygen reduction system is a controlled and continuously monitored indoor climate for extended occupation. This document does not cover unventilated confined spaces that can contain hazardous gases.