Standard on Explosion Protection by Deflagration Venting
NFPA 68 provides requirements for the design, location, installation, maintenance, and use of devices and systems that vent combustion gases and pressures resulting from deflagrations. It is relevant to battery energy storage system (BESS) enclosures and battery rooms where off-gassing from lithium-ion cells during thermal events can create a flammable atmosphere capable of deflagration if ignited.
Published by: National Fire Protection Association (NFPA)
Current edition: NFPA 68 (2023 edition)
Related standard: NFPA 69 (explosion prevention), NFPA 855 (BESS installations)
Scope
NFPA 68 applies to deflagration venting for enclosures containing flammable gases, flammable vapours, or combustible dusts. For BESS applications, it provides the engineering basis for sizing explosion relief panels or vents on battery enclosures or rooms where electrolyte vapours and hydrogen gas from lithium-ion cell venting could accumulate to flammable concentrations.
Key Provisions
Vent Sizing Methodology
NFPA 68 provides equations for calculating the required vent area based on the enclosure volume, maximum allowable pressure (Pred), and the deflagration index (KG) of the flammable gas mixture. For lithium-ion battery off-gases (mixtures of hydrogen, carbon monoxide, and hydrocarbon vapours), conservative KG values must be used in the absence of specific test data.
Vent Device Requirements
Vent devices must open at or below the design activation pressure, have sufficient flow area, and be designed to prevent re-closure during the venting event. Flame arrestors may be required on vent outlets to prevent ignition of vented gases outside the enclosure.
Disclaimer: This is not a definitive guide, just an indication and it is important that you always go back to the source for legislation.
References
- NFPA 68 (2023), NFPA
See also
Thermal Runaway – the gas release event that deflagration venting is designed to relieve safely if it ignites.