Battery Room Ventilation — IEEE 1635

Hydrogen evolution and minimum ventilation rates for stationary battery rooms per IEEE 1635 / ASHRAE.

H2 Evolution

H2 Evolution Rates from Stationary Batteries (IEEE 1635) · Source: IEEE 1635-2018 Table 1 / Eq (A.1); IEC 62485-2 §7.2

Battery type	Mode	Igas per 100 Ah (mA)	H2 evolution (ft³/hr per 100Ah)	H2 evolution (m³/hr per 100Ah)	Notes
Vented Lead-Acid (VLA/flooded)	Float (normal)	5	0.0088	0.00025	IEEE 1635 Tbl 1
Vented Lead-Acid (VLA/flooded)	Equalize	20	0.0353	0.001	4x float per std
Vented Lead-Acid (VLA/flooded)	Boost/overcharge	50	0.0883	0.0025	Worst case design
VRLA (AGM)	Float (normal)	0.5	0.00088	2.5e-05	IEC 62485-2 tbl 1
VRLA (AGM)	End-of-life/fault	5	0.0088	0.00025	95% recombination assumed
VRLA (Gel)	Float (normal)	0.5	0.00088	2.5e-05	IEC 62485-2
NiCd pocket plate	Float (normal)	10	0.0177	0.0005	IEC 62485-2 tbl 2
NiCd pocket plate	Equalize	35	0.0618	0.00175
Li-ion LFP/NMC	Normal	0	0	0	Treat per UL 9540A gas test
Li-ion (fault, thermal runaway)	Worst case	n/a	n/a	n/a	Use UL 9540A + site specific
IEEE 1635 Gas Rate Equation
Q_H2 (m³/hr) = 0.42 x 10⁻³ x I_gas (A) x N_cells (per IEEE 1635 §A.1)
I_gas = I_float x f_g where f_g from table above (fraction of I that produces gas)
Ventilation flow (m³/hr) = Q_H2 / 0.01 [maintains H2 < 1% = 25% of LEL]
Equivalent in ft³/min (CFM) = (Q_H2 x 35.31) / 60

Ventilation Rates

Minimum Ventilation Rates — Stationary Battery Rooms · Source: IFC 2021 §1207, NFPA 1 Ch 52, IEC 62485-2 §7.4, ASHRAE 62.1

Application	Min CFM/ft² floor	Min ACH	Trigger / Notes
Battery room (general, lead-acid VLA)	1	5	IFC 1207.4.1 continuous or H2-activated
Battery room (VRLA)	0.5	1	IEC 62485-2 minimum
Battery room (NiCd flooded)	1	5	Higher Igas than VLA
Battery room (Li-ion)	0.5	1	NFPA 855 §9; per UL 9540A results
Forklift/UPS charging area <50 cells	0	0	Exempt IFC 1207.4.3 Exception
Emergency ventilation on H2 detection	1	12	2% H2 triggers per IFC 1207.4.2
Electrolyte storage area	0.5	6	NFPA 30B if flammable
Control room / annex (personnel)	0.06	0	ASHRAE 62.1 Tbl 6.2 (20 cfm/person)

Sizing Example

Worked Example: 60-Cell VLA UPS Battery Room

Battery type	VLA flooded
Capacity (Ah @ 8hr rate)	1000
Number of cells	60
Nominal float current (A) [0.5% of C]	5
Equalize current (A) [2% of C]	20
Room floor area (ft²)	200
Room height (ft)	10
Room volume (ft³)	2000
FLOAT MODE
Q_H2 (m³/hr) = 0.42e-3 x 5.0 x 60 =	0.126
Q_H2 (ft³/hr) =	4.45
Min vent CFM (for <1% H2) =	7.4
ACH in a 2000 ft³ room =	0.22
EQUALIZE MODE (design basis)
Q_H2 (m³/hr) = 0.42e-3 x 20.0 x 60 =	0.504
Q_H2 (ft³/hr) =	17.8
Min vent CFM =	29.7
BUT IFC minimum 1 CFM/ft² x 200 ft² =	200
Design ventilation rate (takes IFC max):	200 CFM continuous
H2 concentration at 200 CFM = Q_H2/Q_vent =	0.15% (safe; <25% LEL)

Code Refs

Governing Codes & Standards Cross-Reference

Standard	Section	Requirement
IEEE 1635-2018	§4.4	H2 dilution target: max 1% by vol (25% LEL)
IEEE 1635-2018	Annex A	Q_H2 = 0.42e-3 x I_gas x N_cells [m³/hr]
IEEE 1635-2018	§5	Thermal management: maintain 77°F ± 10°F for VLA design life
IEC 62485-2:2018	§7.2	Gassing current f_g fractions for each chemistry
IEC 62485-2:2018	§7.4	Min ventilation = 0.42e-3 x I_gas x N x 1/(0.04 - 0.01)
IFC 2021	§1207.4.1	Mechanical ventilation of stationary battery systems
IFC 2021	§1207.4.2	H2 detection required; alarm at 1%, shut-off charging at 2%
NFPA 1 2024	§52.3.4	Battery room ventilation continuous during charging
NFPA 855 2023	§9	Li-ion ESS — use UL 9540A test results for gas characterization
UL 9540A	Unit Test	Cell/module/unit level fire & gas release characterization
OSHA 29 CFR	1926.441	Charging area safety: ventilation, eye wash, barriers
ASHRAE 62.1	Table 6.2	Occupancy ventilation only; does not cover H2 dilution

Source: Battery_Room_Ventilation_IEEE1635_Reference_v1.xlsx

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