In the United States there are many standards organizations that fall under the umbrella of the American National Standards Institute (ANSI). All these organizations follow the general ANSI protocol for developing consensus standards.
In the area related to gas detection the International Society of Automation (ISA) has two main committees, ISA12 Electrical Equipment for Hazardous Locations that is to be used in hazardous (flammable/explosive) atmospheres and ISA92, Performance Requirements for Industrial Air Measurement Instrumentation Related to Health and Safety; i.e. performance requirements for portable and fixed gas monitoring systems. The gases covered include oxygen, carbon monoxide, hydrogen sulfide, ammonia and chlorine.
At one time the ISA had separate standards for each gas, but in recent years these have been consolidated into a standard for oxygen monitors [ANSI/ISA-92.04.01, Part I-2007 (R2013) Performance Requirements for Instruments Used To Detect Oxygen-Deficient/Oxygen-Enriched Atmospheres] and a standard for toxic gases monitors [ANSI/ISA-92.00.01-2010 Performance Requirements for Toxic Gas Detectors] along with documents providing advice on installation, operation and maintenance of the monitors.
UL (Underwriters Laboratories) is both a standards organization and an OSHA approved Nationally Recognized Testing Lab with particular emphasis on safety. UL has a standards committee that develops standards for explosive atmospheres, and more recently has adapted many of its explosive atmosphere standards to parallel the International Electrical Commission (IEC) standards IEC 60079-x.
The IEC is an international standards organization that develops standards with the consensus of national standards organizations (ANSI for the United States). Obviously there is considerable overlap between the work of the UL 60079 and the ISA12 committees and both organizations have worked hard to ensure compatibility between them and the IEC standards.
UL and ISA both recognize the inefficiency of having two organizations doing the same work and have agreed to combine the effort. The two organizations have agreed that the ISA12 committee and subcommittees will be transitioned to the UL 60079 committee.
Obviously since many gas monitors are designed to operate in hazardous atmospheres, there is overlap between the work and personnel between the ISA12 and ISA92 committees and under the agreement the ISA92 committee will also be transitioned to UL. ISA will continue its standard development efforts in its primary area of expertise, automation and control systems.