A device installed at the top of a storage tank vent pipe to prevent precipitation from entering the vent pipe, while allowing air to freely enter and vapors to freely exit the vent pipe.

Vent caps intended for use with flammable liquids must direct vapors exiting the vent pipe horizontally or vertically to promote the dispersion of flammable vapors so they do not accumulate at the base of the vent pipe.

See also PEI/RP300.