For anyone contemplating a propane conversion on their on-the-road vehicle, only permanently-mounted ASME motor fuel tanks are permitted. Many propane conversion web sites and discussions on internet forums recommend the use of DOT lift truck fuel tanks. These are 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, a motor fuel tank's much greater capacity virtually eliminates the possibility of running out fuel from a single day of off-roading.

The main reason that DOT tanks are dangerous for use in motor vehicles that they are not designed to withstand collisions. 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 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 fittings of tank mounted inside a vehicle.

Annex G

Until recently, both Canada and the USA shared the same design standards in fuel tanks. However, a horrific crash in Carseland, Alberta in 1991 lead to new Canadian fuel tank standards. The Carseland crash involved a propane-fuelled school bus that was rear-ended by a transport truck with the loss of three lives. The accident investigation revealed that the tank was a manifold tank and broke where the crossover tubes connected the tanks when the impact drove the tank into the axle. After the investigation was completed, the findings stated that the victims would have been killed no matter which fuel was used. Propane was absolved of any contribution to the deaths. The investigation stated the force of the collision was so extreme that it is unlikely anyone could have survived an accident of this nature. (Information courtesy of the Fuels Forum member C3H8)

The accident review committee did make recommendations that manifold tanks should undergo a crush test to ensure that the connecting tubes would not break in collisions. The propane industry agreed to develop a standard for tanks that would address the issues raised by the accident. The University of Alberta was retained to develop the test. The test required in Annex G now is a variation of the U of A test.

The propane industry convened a committee of manufacturers, equipment distributors, propane distributors and regulators in Alberta to develop the standard to address the issues raised by this accident. A number of issues were brought forward by the parties, not just those pertaining to the crash.

Annex G addresses far more than crush testing. Crush testing is only one of seven requirements that all propane motor fuel tanks must meet:

• Crush testing also only applies to manifold tanks.
• In addition, all tanks mounted outside a vehicle must have a 25% corrosion allowance.
• The tank openings shall have specific protection requirements.
• All tank brackets must be supported with design calculations or physical testing to meet the loading requirements of CSA B149.5 and these calculations must be submitted with the CRN application.
• Valve guards for all tanks must be designed and tested to meet certain impact loads and undermount tanks need to meet the additional requirements that the guard tabs will not fail or deform the shell above a certain amount.
• Name plates must be either on standoffs or seal welded with NDE to prove the weld integrity.
• Finally all vessel appurtenances must be of corrosion resistance construction and compatible with the vessel material.

Examples of tank bracket differences:

Sleegers 16x36 cylindrical tank installed in an Impala.

Manchester 16x34 cylindrical tank installed in an Impala.

Notice that there is much more weld attaching the bracket to the tank on the Sleegers tank. In a severe collision, this means that there is less likelihood that the g-forces from the impact will tear a hole in the tank.

Tank Manufacturers

There are pretty much only two ASME LPG tank manufacturers for the North American market at this time: Sleegers Engineering in Canada and Manchester Tank in the USA. Both make excellent tanks and both have their own design features. Both Manchester and Sleegers make Annex G-certified tanks.

An important design difference between Sleegers and Manchester is the vapour box. Many installers find that running hoses inside the box is easier with Manchester's design.

Sleegers 16x36 cylindrical tank installed in an Impala. This tank meets CSA B51 Annex G and NFPA 58.

Manchester 16x34 cylindrical tank installed in an Impala. This fuel tank meets NFPA 58.

In Canada, all new propane conversions must use propane fuel tanks certified to meet Annex G. In Ontario, TSSA has issued an Annex G advisory: Propane Tanks For Highway Vehicles.

For their US customers, Sleegers sells tanks designed to US standards due to their slightly lower cost of construction. If you are in the USA, you may purchase and install Canadian tanks meeting Annex G in your conversion for an extra margin of safety because they meet or exceed the requirements of NFPA 58. The extra margin of safety is well worth the added cost.