OHSAS 18001 was created via the concerted effort from a number of the worlds leading national standards bodies, certification bodies, and specialist consultancies. A main driver for this was to try to remove confusion in the workplace from the proliferation of certifiable OH&S. specifications.
A perhaps would be expected, a number of older documents were used in the creation process. These included:
•    BS8800:1996 Guide to occupational health and safety management systems
•    Technical Report NPR 5001: 1997 Guide to an occupational health and safety management system
•    SGS & ISMOL ISA 2000:1997 Requirements for Safety and Health Management Systems
•    BVQI SafetyCert: Occupational Safety and Health Management Standard
•    DNV Standard for Certification of Occupational Health and Safety Management Systems(OHSMS):1997
•    Draft NSAI SR 320 Recommendation for an Occupational Health and Safety (OH and S) Management System
•    Draft AS/NZ 4801 Occupational health and safety management systems Specification with guidance for use
•    Draft BSI PAS 088 Occupational health and safety management systems
•    UNE 81900 series of pre-standards on the Prevention of occupational risks
•    Draft LRQA SMS 8800 Health & safety management systems assessment criteria
It is worth noting that the certification bodies involved in creation hold about 80% of the world market for management system certification.
OHSAS 18001 has been developed to be compatible with the ISO 9001 (Quality) and ISO 14001 (Environmental) management systems standards, in order to facilitate the integration of quality, environmental and occupational health and safety management systems by organizations, should they wish to do so.
The (OHSAS) specification gives requirements for an occupational health and safety (OH&S) management system, to enable an organisation to control its OH&S risks and improve its performance. It does not state specific OH&S performance criteria, nor does it give detailed specifications for the design of a management system.
The OHSAS specification is applicable to any organisation that wishes to:
•    Establish an OH&S management system to eliminate or minimise risk to employees and other interested parties who may be exposed to OH&S risks associated with its activities
•    Implement, maintain and continually improve an OH&S management system
•    Assure itself of its conformance with its stated OH&S policy
•    Demonstrate such conformance to others
•    Seek certification/registration of its OH&S management system by an external organisation
•    Make a self-determination and declaration of conformance with this OHSAS specification.