Why you should never carry LP cylinders lying down on their side

By Russ and Tiña De Maris
The propane attendant readied to sling our seven-gallon cylinder in the back of the car. “Would you mind setting it upright, please?” we asked. He shrugged his shoulders and said, “You know, it really doesn’t matter. It’s safe whether it’s standing up or lying down.” But he put it upright, as we asked. It begs the question: Is it safe to carry LP cylinders lying down? For that matter, is it legal?

The “why” behind the admonishment

Most have heard that LP cylinders should be transported upright. Rarely do we get the “why” behind the admonishment. There’s a good reason, though, as we learn from Magnus Olsson, a safety engineer with Linde, an international firm that deals in pressurized gases. Olsson says it comes down to a safety valve, built into the propane cylinder’s shut-off valve. The safety valve has a pretty limited role in the “LP stage play.” If pressure in the cylinder builds up too high, endangering the integrity of the vessel, the safety valve opens, releasing the pressure.

What happens if the LP cylinder is lying down? The safety valve is no longer at the “top” of the configuration. When the valve is at the top, should it open, it will vent LP vapor. But if the cylinder is lying down, one or two different things could happen—both of them bad. One possibility is that the safety valve could clog, failing to release the excess pressure. The other, the safety valve, will work as designed, but instead of LP vapor, liquid propane can come out of the valve.

Here’s the problem: While LP vapor is flammable enough, a small amount is less likely to get you in trouble. But if liquid comes out of your cylinder—liquid petroleum—it will expand. Exponentially. Read it this way. If, say, a liter of liquid petroleum hits the atmosphere outside of the cylinder, you’ll quickly end up with 250 liters of flammable vapor. No, it’s a stretch to say your 5-gallon cylinder would vent a whole liter of liquid petroleum, but you get the picture. If that vapor finds a source of ignition inside your rig, then hope your life insurance is paid up.

What could “trip” a safety valve?

Still, what’s the likelihood of your LP cylinder safety ever tripping? Again, it would take high pressure in the cylinder to set off a safety valve. What could cause that? Propane gas supplier Levco says, “Temperatures would need to reach higher than 120 degrees Fahrenheit or 40 degrees Celsius to cause a rupture,” or a safety valve release. Most of us don’t need to worry about hitting those kinds of temperatures, right?

What if your LP cylinder is lying down in the back of your SUV on a hot sunny day? A study conducted in Arizona showed that a car parked in the sun for just an hour on a 100-degree day can shoot the cabin temperature up to 116 degrees. Park a little longer, and you could easily test your LP cylinder safety valve effectiveness.

This is another reason to think about what color you might repaint your LP cylinders. Off the shelf, most are brilliant white, or at least a good “highly reflective” color. Folks tricking out an older RV might be tempted to give everything a nifty matching paint job. Fine, paint the siding on your Shasta chocolate brown if you must. Just leave the LP cylinders bright. The darker the color, the less the heat reflectivity, and the greater the likelihood of overheating the contents of the cylinder.

And that legal stuff

Safety aside, there are legal considerations about transporting LP cylinders. The federal regulations that apply come from the Department of Transportation. Here’s a note about how much propane you can legally carry in your rig from lpgasmagazine.com. “A person must carry no more than four propane cylinders in a sedan or SUV at one time. No single cylinder should contain a propane capacity of more than 45 pounds, and the total combined weight of all the cylinders in an enclosed vehicle should not exceed 90 pounds.” With propane scaling in at approximately 4.2 pounds per gallon, the upper limit is about 21 gallons. Three 7-gallon cylinders is the maximum for inside a vehicle.

But suppose you get elected to haul all the empties from the big campout you and your buddies put on? If you haul those cylinders outside—in an open truck bed or on a trailer, the rules change.

Lpgasmagazine.com comments on this: “Customers may transport up to 1,000 pounds of propane in the back of an open pickup truck or trailer. However, the propane cylinders must still be transported in the vertical and upright position.” We’ll use 5-gallon cylinders here—the math’s easier. You can move 200 of them at a time.

Keeping them upright

Keeping LP cylinders upright and secure can be a bit of a trick. One of the patriarchs in our family would have described the design of these gas containers as “tippy-arsed.” And indeed, left on their own, the slightest rocking motion will dump your typical cylinder over. Several outfits make plastic bases that LP cylinders can be set into for transport. Here’s one from Flame King, sold on Amazon.com. For about $30 a pop, these might be the answer.

Many RVers use milk crates to keep their cylinders upright. But unless you’ve got a friend in the milk distribution business, we found milk crates on Amazon cost more than these plastic rings made for the job. We don’t encourage sneaking around behind grocery stores to “pick up” a crate or two. Spending a few bucks on a “real” stabilizer is probably easier than time in the hoosegow for a “free” milk crate.

Of course, if you transport LP in the back of your pickup, you might try a method that one of our readers has done. He’s designed an extremely sturdy and efficient “tie down” system. Check out our story, Safely carry LP cylinders in your pickup with this clever mod.

In any event, don’t transport your LP cylinders lying down. You could be asking for a personal disaster that’s easily avoided.

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