Ventilate the battery space and plan for venting gas
Lead acid batteries give off hydrogen when charging. Any lithium battery that fails can vent a flammable, toxic gas cloud with or without flames. Design the space for both.
How
- Ventilate lead acid batteries so hydrogen stays well below its 4% lower explosive limit (ZVEI).
- The IEC 62485-2 method sizes airflow from the number of cells, battery capacity and a gassing current. One maker's vented cell figures are 5 mA per Ah on float and 20 mA per Ah on boost charge.
- For natural ventilation that maker asks for inlet and outlet openings of at least 28 cm2 per m3/h of required airflow. Use your own battery maker's figures.
- Lithium batteries in thermal runaway effectively always produce a flammable gas and vapour mix, including carbon monoxide, hydrogen and methane (UL FSRI). This is true of LFP as well.
- Battery gas can be released with no fire at all. It shows as white or grey vapour, often in low-hanging clouds (US Fire Administration).
- The US Fire Administration warns that the timing and severity of a battery gas explosion is unpredictable. Fire crews are told not to go in just to take gas readings.
- So put batteries where venting gas cannot drift into rooms where people sleep or gather, and where nobody has to walk past them to escape.
- Write on the shutdown plan: if you see white or grey vapour from a battery, do not open the room or go in. Get everyone out and call the fire service.
Safety: Never enter a room with venting battery gas, even to switch something off. The gas is toxic and can explode without warning.
Do these first
Sources
- Installation, commissioning and operating instructions for vented stationary lead-acid batteries (V1.4, 2018). HOPPECKE Batterien, accessed 2026-11
- Information leaflet 14: Ventilation of battery charging rooms for lead traction batteries (2020). ZVEI, Batteries Division, accessed 2026-11
- Experiments Investigating Explosion Hazards from Lithium-ion Battery Thermal Runaways in Residential Garages Conclude. UL Solutions Fire Safety Research Institute (FSRI), accessed 2026-11
- Responding to Fires that Include Energy Storage Systems Using Lithium-ion Battery Technology are a New and Evolving Hazard. US Fire Administration (FEMA), accessed 2026-11