The primary source of heat for a hot air balloon is propane. A pilot should be familiar with propane and the balloon's fuel system in order to properly manage fuel and refuel safely.

Properties of Propane

Propane is a colorless, odorless flammable gas (C3H8) found as a by-product of natural gas and the production of gasoline. Since pure propane has no smell; it is odorized with a warning agent.

Liquid petroleum gas (LPG) includes propane and butane. Propane is a gas at normal temperatures, but will liquefy under moderate pressure. It is usually stored in liquid form and is burned in vapor form. The potential fire hazard for propane is similar to that of natural gas, except that propane is heavier than air and will sink to the ground.

The boiling point of pure propane is -44'°F. Since vaporization is quick at normal temperatures; propane does not present a flammable liquid hazard.

Propane is particularly suitable as fuel for hot air balloons because it is low in weight (4.2 pounds per gallon), high in thermal output, and its moderate tank pressure requires no pumps to deliver it to the balloon heater system. Propane is readily available at a reasonable price, clean, and safe.

Propane does have some disadvantages. Propane vapor is invisible, making it difficult to detect, and is heavier than air, which makes it pool or gather in low places. It is also very cold; giving freeze burns to skin if handled incorrectly.

Balloon Propane Tanks

Propane tanks used in hot air balloons are mainly constructed of either aluminum or stainless steel. Most aluminum tanks are vertical 10-gallon cylinders (DOT 4E240), built primarily for forklift trucks. Stainless steel tanks are either vertical or horizontal, of many different sizes, and built especially for hot air balloons. [Figure 5-1]

All balloon cylinders have liquid service valves, excess-pressure relief valves, and liquid level indicator valves. Many tanks have vapor service for pilot lights and some have an emergency valve or filler valve. Some tanks may have as many as five individual service valves, and some have only one combination (3-in-1) valve. There is no standard valve configuration for balloons. Generally, the large valve handle is liquid and the smaller handle is vapor; tanks and/or handles are usually labeled.

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