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Hydrogen Gas Ventilation Calculator for Forklift Battery Charging Area

Lead acid motive power batteries produce hydrogen gas and other fumes at 80% recharge point, making proper ventilation in the battery charging area extremely important.

Hydrogen gas is not only colorless and odorless, but is lighter than air, causing the gas to rise to the top of a building. For safety purposes, the concentration of hydrogen in the air should be kept below 1% to reduce risk of explosion.

The calculators provided below are for reference only and BHS takes no responsibility for these guidelines or the results obtained. Applicable statutes and regulations supersede any guidelines provided by BHS. The calculations represent worse case scenario assuming all batteries are producing hydrogen gas at the same time.

Note: These formulas are designed for lead acid motive power batteries. It should not be used for valve regulated, floating charge batteries that are commonly used in uninterrupted power supply systems.

To properly monitor and exhaust hydrogen gas, BHS supplies the Hydrogen Gas Detector, Hydrogen Exhaust Fan Kit, and Battery Room Ventilation System.

Hydrogen Generation

Select Number of Battery Types:

Battery Group 1

Number of cells in one battery
6-hr rated capacity of battery (amp/hrs)
Number of this size of battery
Volume produced by this battery:

XXX cubic feet per hour

XXX liters per hour

The following equation can be used to estimate the volume of hydrogen gas produced (H) during recharge of a lead acid battery.
H = ((C x O x G x A) / R)/100     Where:
C = Number of cells in the battery
O = Amount of overcharge during recharge, assume 20%
G = Volume of hydrogen produced by one amp hour of charging, use 0.01474 for cubic feet
A = 6-hour rated capacity of the battery in amp hours
R = Number of hours battery is overcharged, assume 4 hrs
Volume of hydrogen gas generated during charge:
XXX cubic feet of Hydrogen gas (XXX liters) per hour

Room Volume

Room Width ft
Room Length ft
Room Height ft
Total volume of battery room:
XXX cubic feet
Room Volume = Width * Length * Height
Ventilation Requirement = R x P ÷ H x 60min
R = Volume of room
P = Maximum percentage of Hydrogen allowed
H = Total hydrogen produced per hour


As an industry standard, the maximum percentage of hydrogen gas allowed within a room should not exceed 1%. This can be estimated by comparing the volume of the room to the amount of hydrogen that could potentially be produced within an hour. If the level in your battery room exceeds 1% after one hour of charging, normally forced ventilation would be recommended. Based on the numbers provided, your room would be at:
XX% after 1 hour.
Regardless of this estimation, a few additional points should be considered before a decision is made.
  • Is the battery room closed in or open to outside air? If the room is enclosed, natural ventilation may not be possible.
  • Are there areas in the ceiling where hydrogen gas could accumulate in greater concentrations? Pockets in between roof trusses and building column could potentially create pockets where hydrogen could accumulate to hazardous levels.

Ventilation Requirements

Based on your information, there will be XXX cubic feet of hydrogen gas produced per hour in a room with a volume of XXX cubic feet. Therefore the air in the room will need to be completely exchanged every XX minutes to maintain a safe level of hydrogen gas.
Complete Air Exchange Every XX Minutes

Exhaust Fan Requirements

To accomplish this, an exhaust fan(s) will be required that is rated for:
XX cubic feet per minute