Propane is a saturated low-pressure gaseous hydrocarbon fuel (C3H8). It is often called a liquefied petroleum gas (LP Gas or LPG), and used as a combustible.
Since propane is odorless, Mercaptan, a colorless gas with a putrid smell, is added, to help detect any leakage.
It is heavier than air.
Since propane is generally used under its gaseous form, storage tanks are generally filled to 80% of their capacity, allowing the gas to expand and liquefy as it travels towards your device.
One litre of propane yields approximately 25000 btu/hour
The Material Safety Data Sheet of your device will indicate its power.
For example: a 35000 btu fireplace: 350000 divided by 25000 equals 1.4
Therefore, this device uses approximately 1.4 litre per hour.
It is perfectly safe to leave the pilot light on, especially in a fireplace, in very cold weather, in order to facilitate the ignition, and to prevent any mist or cold infiltrations from the device's exhaust.
Stay calm and do not light up any device, flashlight, electric bulb, that might ignite the leaking gas.
Close the valve on the tank, by turning it clockwise.
Leave windows and doors open, and immediately call your distributor to request a service call.