This standard provides requirements for installing systems for the prevention and control of explosions in enclosures that contain flammable concentrations of flammable gases, vapors, mists, dusts, or hybrid mixtures. It is intended for use by design engineers, operating personnel, and AHJs.

NFPA 921 sets the bar for scientific-based investigation and analysis of fire and explosion incidents. Referenced in the field, in training, and in court, it is the foremost guide for rendering accurate opinions as to incident origin, cause, responsibility, and prevention. It is intended for use by both public sector employees who are responsible for fire investigation and private sector professionals who conduct investigations for insurance companies or litigation purposes.

Please note:  This Standard is in a custom cycle due to the Emergency Response and Responder Safety Document Consolidation Plan (consolidation plan) as approved by the NFPA Standards Council.  For revision cycle information, see the Next Edition tab.

This standard applies to the design, location, installation, maintenance, and use of devices and systems that vent the combustion gases and pressures resulting from a deflagration within an enclosure so that structural and mechanical damage is minimized.

This guide provides criteria for the design, installation, and operation of piping systems that contain or may contain flammable vapor mixtures to prevent and protect against damage from deflagrations or detonations due to combustion of flammable atmospheres therein.

This standard provides minimum safety requirements for the cleaning and purging procedures of flammable gas piping systems, including cleaning new or existing piping systems, purging piping systems into service, and purging piping systems out of service.