5 foot minimum between relief valve discharge and external source of ignition (ait conditioner,) direct vent, or mechanical ventilation system (attic fan).
If the DOT cylinder is filled on site from a bulk truck, the filling connection and vent valve must be at least 10 feet from any external source of ignition, direct vent, or mechanical ventilation system.
Location of ASME Containers
Regardless of its size, any ASME tank filled on-site must be located so that the filling connection and fixed level qauge are at least 10 feet from external sources of ignition (i.e. open flame, window A/C, compressor, etc), intake to direct vented gas appliance or intake to a mechanical ventilation system.
May be reduced to a 10 feet minimum for a single container of 1200 gallons water capacity or less if it is located at least 25 feet from any other LP-Gas container of more than 125 gallons water capacity.
Minimum distances from underground containers shall be measured from the relief valve and filling or level gauge vent connection at the container, except that no part of the underground container shall be less than 10 feet from a building of line of adjoining property which may be built upon.
Where the container may be subject to abrasive action or physical damage due to vehicular traffic or other causes it must be either, (a) placed not less than 2 feet below grade; (b) otherwise protected against such physical damage.