Meaning
Total amount of gas released by a cell or battery during a thermal runaway event, measured under standardized temperature and pressure conditions. In battery safety assessment, the off-gas volume represents the primary variable used to determine the capacity of the ventilation and explosion relief systems. This metric governs the dilution rate needed to keep flammable gas concentrations below their lower explosive limit.
It ceases to apply once venting has concluded and the battery chamber returns to a stable, non-reacting state. Accurate measurement of this volume is necessary to comply with international fire codes and transportation safety standards.
Measurement Technique
Characterizing the emissions involves heating a cell to failure within a sealed autoclave equipped with gas chromatography and pressure sensors. This laboratory setup determines the off-gas volume and the chemical composition of the discharged gases under inert or air atmospheres. The collected data allows engineering teams to calculate the rate of gas generation and the corresponding pressure development over time.
Ventilation Sizing
Designing exhaust systems for energy storage rooms depends heavily on the total gas generation during the worst-case failure scenario. If the off-gas volume exceeds the extraction capacity of the exhaust fans, flammable gases will accumulate near the ceiling of the enclosure. Safety systems must use these volumetric values to schedule sufficient fan power to maintain safe air changes.
Dilution Strategy
Preventing explosive atmospheres requires mixing the discharged compounds with fresh air to lower the local concentration below hazardous thresholds. When a high off-gas volume is expected, active safety systems must inject nitrogen or run exhaust fans at peak speeds to disperse the plume. This protective measure prevents secondary deflagration outside the primary battery containment area.
