Battery Flame Arrestor Vent Caps

Battery Safety and Flame Arrestors
During normal operation, all lead-acid batteries emit an explosive mixture of hydrogen and oxygen gas which is produced by a chemical process known as electrolysis. A nearby spark or flame may cause the gas to ignite and result in an explosion, causing shrapnel and battery acid to be propelled in every direction. To help prevent this and reduce the risk of injury, safety precautions should be observed whenever you are within close proximity to a battery. Protective clothing and gloves should be worn along with protective goggles, preferably an impact resistant transparent face shield. Open flames, smoking, or sparks must be avoided. Read and follow all safety instructions provided by the battery manufacturer. The risk of explosion can be reduced by replacing standard battery vent caps with models that contain a flame arrestor.

What is a battery flame arrestor?
A flame arrestor is a porous filter which allows battery gases to escape through it, but prevents a flame from entering the battery. They are often made of polypropylene or polyethylene, and are available in a variety of shapes. The size of the individual pores is measured in microns, and is carefully controlled in the manufacturing process to allow gas to flow through the filter at a specified rate, thereby preventing a buildup of pressurized gas within the battery.

How does a flame arrestor function?
To reduce the risk of a battery explosion, some manufacturers install a flame arrestor in their battery vent caps. A flame arrestor prevents a battery from exploding by preventing a flame from entering the battery and igniting the internal gases. There are currently no laws requiring this feature, thus some vent caps contain a flame arrestor while others do not. This added feature increases the cost of vent cap by approximately 50 cents, but not every consumer is willing to pay extra for the added safety.

A flame arrestor by itself does not actually extinguish a flame; it merely stops it from progressing into the battery where it can ignite the internal gas. Since battery vent caps (and flame arrestors) are usually made of polypropylene which is flammable, if the flame continues to burn, eventually the vent cap and flame arrestor will melt which may result in a battery explosion. Therefore a separate technology should be employed to extinguish the flame. We have observed that not all safety vent caps are designed with that capability. When selecting a vent cap, it is advisable to verify if it has been tested and certified by an independent lab to actually extinguish the flame in addition to preventing an explosion. Although a certified vent cap greatly reduces the risk of an explosion, the risk can never be completely eliminated. The recommended safety precautions should always be observed regardless of whether a flame arrestor is present or not.

Should vent caps be loosened when charging a battery?
For safety reasons, it is very important that all battery vent caps should always remain tightly sealed, especially while charging the battery. A greater volume of hydrogen gas is produced during the charging process. Vent caps that are not securely tightened will result in a gap between the gasket and the vent cap, increasing the risk of fire and explosion. Vent caps should only be removed when checking the level of the electrolyte, or when adding water to the battery.