How is the area classified within 5 feet of the open vent of an aboveground tank?

The correct classification for the area within 5 feet of the open vent of an aboveground tank is Class I, Division 1. This classification is based on the presence of flammable vapors that could be released from the tank or its vent. In this scenario, the open vent is a potential source for the escape of flammable vapors, creating an environment where the concentration of these vapors can be sufficient to ignite if there is an ignition source present.

Class I areas are defined as those where flammable gases or vapors may be present under normal operating conditions. Division 1 indicates that the conditions under which the flammable substances are present can be frequent or continuous, which is the case near an open tank vent.

In contrast, Division 2 areas are those where flammable vapors are not likely to occur in hazardous concentrations under normal operating conditions but may occur due to occasional leaks or spills. Thus, since the open vent can continuously release vapors, the correct classification accurately reflects the potential hazard in this area.