Battery Flame Arrestor Vent Caps

Battery Flame Arrestors
During normal operation, all lead-acid batteries emit a 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. To help prevent this, certain steps should be followed whenever you are within close proximity to a battery. Heavy work clothing along with an acid proof apron and gloves should be worn along with goggles and an impact resistant transparent face shield. Open flames, smoking, or sparks must be avoided. Read and follow all instructions provided by the battery manufacturer. The chances of ignition 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, 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?
Some manufacturers install a flame arrestor in their battery vent caps. A flame arrestor prevents the combustion of internal battery gases by preventing a flame from entering the battery. 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 this feature.

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. Therefore a separate technology should be employed to extinguish the flame. We have observed that not all battery 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. Although a certified vent cap greatly reduces the chances of igniting the internal battery gas, that possibility cannot be completely eliminated. The procedures that are recommended  by the battery manufacturer should always be followed regardless of whether a flame arrestor is present or not.

Should vent caps be loosened when charging a battery?
It is very important that all battery vent caps should 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, resulting in the flame arrestor becoming inoperative. Vent caps should only be removed when checking the level of the electrolyte, or when adding water to the battery.