Propane is one of a group of chemicals known as hydrocarbons and it is one of several natural gas liquids or NGLs that are captured for commercial use: ethane, butane and pentane are three other common NGLs. Propane and butane are sometimes referred to as liquefied petroleum gas or LPG.

All propane sold for domestic consumption in Canada must meet the HD5 standard. This spec requires propane to be at least 90% pure, although most product today is over 95% pure propane. The balance is made up of other hydrocarbons like ethane and ethylene (7.5% max.), propylene (5% max.), butane (2.5% max.) and pentane (0.5% max.). Sulfur content must not exceed 116 parts per million.

Knowing something about propane’s characteristics can help a person understand why propane must be handled and stored in certain ways.

• Propane in its natural state is colourless and odourless. A powerful stench odorant, called ethyl mercaptan is added to aid in the detection of leaks. Its odour resembles boiling cabbage.
• Propane is non-toxic but if it displaces enough air, asphyxiation could occur.
• Propane gas is about one and a half times heavier than air, so in case of a leak it would tend to settle in low areas rather than dissipate.
• About 23.5 cubic feet of air is required to burn one cubic foot of propane. At that ratio, combustion is nearly complete, leaving behind nothing but water vapor and carbon dioxide.
• Propane’s boiling point is -42°C. Propane remains in a liquid state at temperatures colder than that point. At temperatures above that point, unless the propane is contained, it would begin to boil and the liquid would simply vaporize into the air, like steam from a kettle of boiling water.
• Vapor pressure is the term used to describe the push that propane gas exerts on the wall of the container it is stored in. Typically measured in pounds per square inch (psi), the pressure inside a container will rise and fall in relation to temperature. The higher the temperature, the higher the pressure becomes in the container. For example, while the pressure inside a container of propane will be about 50 psi at 0°C, on a hot summer day the pressure will rise to over 100 psi. Propane containers are designed and built to safely withstand pressures many times higher. However, they must never be filled beyond 80% of their capacity to allow for an increase in vapour pressure.
• If you were able to see through the steel wall of a propane container, you could see that liquid propane looks just like water. And while it wouldn’t be visible, a head of propane gas would also be present. If you were to open the container valve the gas would begin to escape, lowering the vapor pressure and allowing the liquid propane to boil, which would in turn produce more propane gas. This process would continue until the tank was empty or until the temperature dropped below -42°C.
• In order to vaporize, liquid propane will absorb heat from anywhere it can get it. If you were to splash liquid propane on your skin, for example, the propane would immediately draw out the warmth and produce a freeze burn. Consequently, anyone working with propane should wear long sleeves and neoprene gloves.
• While propane is normally burned as a gas it isn’t practical to store or transport it in that form. Consider that one volume of liquid propane is equal to 270 equal volumes of propane gas. So, for example, if you put one litre of liquid propane into a 270 litre container, the liquid would simply vaporize and the resultant gas would occupy the entire container. Therefore, propane is compressed into liquid form so that it can be more easily, stored and transported.
• Technically speaking propane bulk tanks are referred to as pressure vessels and must adhere to strict federal standards in both their manufacture and installation.
• Pump attendants must inspect all customer cylinders before filling to ensure they meet standards.
• Pump attendants must ensure that there are no sources of ignition in the vicinity before they fill a propane container.
• Pump attendants should ensure that their customer’s cylinders are transported in a secure, upright position, in a well ventilated space.
• Propane is classified as a Dangerous Goods product. As a result, anyone that dispenses propane must be trained and certified.