For anyone contemplating a propane conversion on their on-the-road vehicle, only permanently-mounted ASME motor fuel tanks should be considered. Many propane conversion web sites and discussions on internet forums recommend the use of DOT lift truck fuel tanks. These are generally illegal and dangerous for use in on-road vehicles.

The off-roaders like the DOT tanks because they are portable and they can change out a fuel tank on the trail if they run out. Fork lift tanks are available in 20, 33.5, and 43.5 lb sizes. Liquid propane's specific volume is 8.547 ft³/lb which corresponds to 4.24 lb/gallon (US) 5.1 lb/gallon (Imperial). Therefore, this corresponds to capacities of 4.72, 7.90, and 10.26 US gallons. However, an ASME motor fuel tank's much greater capacity virtually eliminates the possibility of running out fuel from a single day of off-roading.

Manchester Tank (a manufacturer of both ASME and DOT tanks) does not recommend that their DOT lift truck cylinders be used for over-the-road engine fuel use as they were not designed for that purpose.

CSA B149.5 (Installation Code for Propane Fuel Systems and Tanks on Highway Vehicles) prohibits the use of DOT tanks in on-road vehicles. Although NFPA 58 (Liquefied Petroleum Gas Code) permits the use of these tanks in on-road vehicles, other requirements of NFPA 58 (free to view on-line) make the use of these tanks non-compliant. The reasons that DOT tanks are dangerous for use in motor vehicles that:

• DOT tank brackets are not certified to withstand collisions.
• DOT tank venting from safety relief valves is difficult to make compliant with NFPA 58.
• The appurtenances (fittings) on DOT tanks can NOT be enclosed in a vapour box for vehicle interior installations.

Plain and simple: ASME tanks are designed for use in motor vehicles and DOT tanks are designed for lift trucks. If you have an off-road vehicle and decide to use a DOT tank, do NOT mount it inside the vehicle. A spark from a switch (from opening the door, etc) can set off an explosion from a leaking fitting or from the blow-off of the safety relief valve. You must have a vapour box around the appurtenances of tank mounted inside a vehicle.

NFPA 58

In Canada, CSA B149.5 specifically prohibits the use of DOT cylinders as the permanent fuel tank of a highway vehicle. Although NPFA 58 permits the use of permanent and exchangeable tanks (§11.3.1.8), it is the details of the installation of DOT tanks that make these installations non-compliant. The main issues with using a DOT tank have to do with installation, relief valve venting, and appurtenance enclosure.

§ 11.8.4 Container Installation § 11.8.4.1 Fuel containers shall be installed to prevent their jarring loose and slipping or rotating, and the fastenings shall be designed and constructed to withstand without permanent deformation static loading in any direction of equal to four times the weight of the container filled with fuel.

§ 11.8.5 Pressure Relief Valve Discharge System. § 11.8.5.1 The pressure relief valve discharge from fuel containers on vehicles other than industrial (and forklift) trucks shall be in accordance with the following:

1. It shall be directed upward or downward with 45 degrees of vertical.
2. It shall not directly impinge on the vehicle fuel container(s), the exhaust system, or any other part of the vehicle.
3. It shall not be directed into the interior of the vehicle.

§ 11.9 Installation in the Interior of Vehicles § 11.9.1.3 The container appurtenances and their connections shall be installed in an enclosure that is securely mounted on the container.

1. The appurtenances and their connections shall be installed in an enclosure that is gastight with respect to the driver or passenger compartments or with any space carrying radio transmitters or other spark-producing equipment.
2. The enclosure shall be vented to the outside of the vehicle.

Raso Enterprises Interpretation of NFPA 58

Since DOT tanks do not have integral mounting brackets, they must be fastened to the vehicle with appropriate tank brackets. we are not aware of any brackets that are certified to withstand a 4G load in any direction.

Since DOT-style tanks have protective collars around the appurtenances, without a pipeaway system, any venting of the pressure relief valve will impinge upon the container or flow horizontally.

Since DOT-style tanks are not equipped with vapor boxes around the appurtenances, there no permissible way for them to be installed in interiors of vehicles. That would leave the only potential candidates for this type of tank to be open-bed vehicles such as pickup trucks. Even if your Jeep is always driven with an open top, if there is a soft top that could be installed for bad weather, the possibility of being closed-in makes the bed of the Jeep an interior tank location.

Alternatives

Both Manchester and Sleegers make ASME tanks that are compliant with NPFA 58 in off-road vehicles.