Liquid Propane can be used for a variety of effects. It is non-toxic and easy to work with. However, as with any flammable gas, there are significant safety considerations. Don't ever become complacent when working with or using liquid propane, or even with fire in general.
Liquid propane is sold most often in 20 pound bottles, the type typically associated with BBQ's and patio heaters. The fuel is bottled under pressure which keeps it in liquid form. There is a small amount of air space in the bottle and the liquid propane vaporizes, turns into a gas, to fill that space. The rest of the propane remains in a liquid state. As more of the gas is released from the bottle, more of the liquid vaporizes to fill the empty air space.
The pressure in a LP tank does not vary as the fuel is used. It will remain the same until the fuel is exhausted. The pressure does vary though with temperature. The higher the ambient temperature, the higher the vapor pressure.
Standard operating pressure for LP is around 100 psig, however, higher pressures can be easily reached such as from heating the storage tank in the sun. This is why storage tanks are always painted white, to reflect sunlight.
Liquid propane is heavier than air and thus can pool in low spots if there is not enough air movement to stir it with surrounding air.
Burning LP results in carbon monoxide and soot when it is not burned in what is a called an "ideal burn". While it is possible to achieve ideal burn and safely use propane indoors, the risks of an imperfect burn are significant, especially in an improvised effect. Burning propane should only be used with adequate fresh air ventilation.
LP should not be piped with galvanized pipe. Always use black pipe, stainless steel or brass.
Effects and Uses:
Propane is commonly used in BBQ's. Typical BBQ's have a pipe with a series of small holes in it. When the gas is released and ignited, each hole turns into a tiny flame jet. This same technique can be used to create a fire ring in a fire pit, or to create a torch.
Flow control can be regulated from the propane bottle itself or in-line controls can be added. For fire ball "puffers" an electrically controlled solenoid valve can be used to quickly open and close a supply line. Use of a valve rated for propane gas is important and does not add much cost. In order to ignite the gas a standing pilot is a common easy method. A spark igniter can be used, however, they may not be 100% effective in igniting the gas. Synchronizing the ignition to the flow of gas may also be problematic.
Propane can be bubbled up through water, such as a swimming pool, to create a "fire on the water" effect. Note that the water will warm over time.
Propane can be released beneath sand, such as in a fire pit to create an interesting effect. The sand works as a diffuser to spread out the flame and to keep the flame lit.
In windy situations, a diffuser, such as steel wool can be used near a flame jet to prevent the flame from being extinguished.
Caution: This information is provided as some general guidelines but is not exhaustive. It is provided as-is and you may use it only at your own risk. Any fire project is inherently dangerous and all safety protocols and fire safety laws should be observed.