What is Forklift Battery Gassing and How Do You Manage it?

forklift battery gassing hydrogenNext time you’re in the forklift battery room, look up. You should see an extensive system of vents and ducts above the battery stands — if not, it’s probably time to redesign your charging area. Battery room ventilation systems remove the excess hydrogen that can build up above charging batteries.

But why do forklift batteries leak hydrogen?

Understanding the causes of battery gassing demystifies the charging process, which can help you run a safer and more efficient battery room.

Batteries produce hydrogen as a natural part of charging, and it’s actually a pretty simple process to understand. When you connect your forklift battery to an active charger, electrical current passes into the flooded battery cells. This influx of energy reverses the chemical reactions of the discharge process. Lead sulfate separates into sulfuric acid, lead oxide, and pure lead, and the metallic compounds naturally re-accumulate on their source plates.

All of these chemical reactions have an unintended consequence on the water present in the electrolyte. Above a certain voltage, water begins to break down into its component parts: oxygen and hydrogen. The typical lead-acid forklift battery charger brings water to its decomposition threshold after the cells reach an 80 percent charge. That’s why gassing increases at the end of the charging process.

When enough hydrogen is isolated, it forms bubbles, which float to the top of the electrolyte and right out through the battery vents. Voila — hydrogen gas.

Managing Forklift Battery Outgassing

Now that we’ve got the chemistry out of the way, you should see why forklift battery gassing is an important consideration. Every lead-acid forklift battery leaks hydrogen and oxygen; it’s a normal part of operating the technology.

Even when batteries aren’t in use, natural evaporation and self-discharge lead to a small amount of outgassing. These rates increase dramatically under certain abnormal conditions, like higher temperatures or excessive voltage.

The good news is that the process isn’t a problem for most facilities. There are plenty of reliable technologies to help manage the production of hydrogen. With that being said, forklift battery gassing has a few effects that you will need to address in order to protect your equipment and your facility:

  • Hydrogen Accumulation Above Charging Areas

    – Hydrogen gas is colorless and odorless. It’s also the lightest element in the periodic table, far lighter than air, which means it will always float to the highest point of an enclosed area. You definitely don’t want a layer of hydrogen floating around the ceiling of your warehouse. At a concentration of only four percent by volume, hydrogen becomes a potent explosive hazard — and most published standards recommend keeping hydrogen levels below one percent.The way to maintain this safe concentration is to take advantage of hydrogen’s natural tendency to rise. Vents above battery stands will allow hydrogen to escape harmlessly into the atmosphere. Only charge batteries in a dedicated area, complete with an advanced ventilation system and integrated hydrogen gas detectors.This isn’t just an idle suggestion. OSHA, IEEE, and NFPA regulations all require adequate ventilation for battery charging areas. Of course, forklift battery room ventilation requirements differ from facility to facility. If you’re not sure how your ventilation system stacks up, the BHS Ventilation Calculator can help you get started.

  • Lost Water Content

    – When hydrogen and oxygen leak out of the electrolyte mixture, the water level decreases. Battery room operators should replace this lost water to keep battery cells from oxidizing or experiencing increased sulfation. Keep on top of this vital maintenance task by leaving it up to the BHS Integrated Watering System, which automatically replaces lost water at the end of the charging cycle.If your fleet management software doesn’t track watering, replace it with a system like the BHS Fleet Tracker. This software helps to keep you on schedule with watering and other maintenance tasks. It even displays batteries in order of their placement, so your staff can easily water each battery in a quick, simple sequence.

With the right equipment, gas accumulation won’t be a serious issue for your facility, regardless of the size of your fleet. While battery gassing is inevitable, hydrogen gas management is a relatively simple — and essential — process.


Lead-Acid Battery.” HyperPhysics. Georgia State University Department of Physics and Astronomy, n.d. Web. 21 July 2015.

O’Donnell, Carey and Schiemann, Michael. “Hydrogen Gas Management for Flooded Lead Acid Batteries.Battcon 2008 Conference, Marco Island, FL. PDF. 21 July 2015.