| ||Incidents involving the improper use of propane cylinders have resulted in injuries and fatalities in Alberta. Many users are not aware of the safety risks of using the cylinders for purposes other than what they are intended for. “Propane cylinders are only designed to store and handle propane,” says Allan Hantelmann, technical advisor/boilers and pressure vessels of Alberta Municipal Affairs. “When cylinders are used for alternate purposes, a number of dangerous things happen to the cylinders that can’t be seen with the naked eye.”
When a 20-pound propane cylinder is manufactured, it meets specific requirements set out by the Canadian Standards Association Group. This includes the design, testing, repair, and rebuilding of cylinders to transport propane. Anyone manufacturing, rebuilding, or repairing the cylinder must follow the rules in the standard. If the standards are not adhered do, cylinders can suffer metal fatigue and corrosion/rust, and can ultimately rupture.
The 20-pound cylinders are made from a specific type of manufactured carbon steel, with grain structures that can be seen under a microscope. When the steel is heated or subjected to higher pressures than the cylinder was originally designed to withstand, there is stress and strain put on the grain structure, and tiny movement occurs within the metal itself. This may form a crack that is not readily apparent. When this stress and strain is applied many times, the crack will become larger, the material can become worn-out and burst open. “This is similar to when you bend a paper clip back and forth until it breaks – it’s called metal fatigue,” says Hantelmann.
Filling the cylinder with water and heating it up, or reusing the cylinder to hold compressed air is also hazardous because moisture formed in the cylinder will start the corrosion process. Corrosion will weaken the ability of the cylinder to hold gas or liquid under pressure, which can further weaken the cylinder to the point of rupturing.
Making modifications to the cylinder so it can be used to heat water to produce steam is also extremely dangerous. When water changes from a liquid to steam, it expands 1,700 times its size. When the heated water is contained in a closed cylinder it cannot expand. This puts extreme stress on the steel and can cause it to burst open, sending fragments everywhere.
In addition to the cylinder itself, the opening for the nozzle is also an important part of the safe design of a propane cylinder. According to the Canadian Standards Association Group’s approved design, the head of the cylinder is only designed for one nozzle, using a standard valve fitting. No other nozzles are allowed to be added, at any time during the life of the cylinder. Welding is also not allowed on the cylinder, as it shrinks the cylinder material by approximately 7 per cent, and creates stress on each side of the weld.
Hantelmann says the proper use of propane cylinders is key to safety: “We want to minimize incidents and accidents associated with propane cylinder use in agriculture. And part of this is bringing awareness to the dangers of modifications, and the potential for catastrophic explosions.”
Allan Hantelmann, technical advisor/boilers and pressure vessels
Alberta Municipal Affairs