Morisson's Model 245 is a lightweight, spring-loaded emergency vent (pressure relief only) used on aboveground storage tanks, as a code requirement, to help prevent the tank from becoming over-pressurized and possibly rupturing if ever exposed to fire. This vent must be used in conjunction with a "normal vent". Correct application of this vent requires proper vent size and selection for the tank system in order to meet the specific venting capacity.

Note: Emergency vent should be set higher than the normal vent so the normal vent operates first.