NFPA 69 - Battery Design

Standard on Explosion Prevention Systems

NFPA 69 covers active explosion prevention systems used to suppress or prevent deflagrations in enclosures containing flammable atmospheres. While NFPA 68 addresses passive venting, NFPA 69 covers active systems including oxidant concentration reduction, combustible concentration reduction, explosion suppression, and spark detection/extinguishing. It is relevant to large BESS enclosures where active gas management or suppression systems are used to mitigate explosion risk from battery off-gases.

Published by: National Fire Protection Association (NFPA)
Current edition: NFPA 69 (2022 edition)
Related standard: NFPA 68 (deflagration venting)

Scope

NFPA 69 applies to systems designed to prevent explosions by controlling the concentration of flammable gases or vapours in enclosures. For BESS applications, it provides the engineering framework for inert gas purging systems, gas detection and ventilation interlocks, and suppression systems designed to prevent ignition of battery off-gases in confined spaces.

Key Protection Approaches

Oxidant Concentration Reduction and Combustible Concentration Reduction

Inert gas injection reduces the oxygen level in an enclosure below the limiting oxygen concentration (LOC) for the specific flammable gas, preventing ignition. Alternatively, forced ventilation keeps combustible gas concentrations below 25% of the lower explosive limit (LEL), providing a safety factor against ignition.

Explosion Suppression Systems

Suppression systems detect an incipient deflagration via pressure or optical sensors and discharge suppressant (typically dry powder or gas) within milliseconds to arrest flame propagation before pressure builds to structural damage levels.

Disclaimer: This is not a definitive guide, just an indication and it is important that you always go back to the source for legislation.