If a propane tank runs empty your stove, furnace, grill or any other appliances on propane won't work and the flame will go out.
If the propane tank runs empty it can also cause air in the system if you have a whole house propane tank and you will often need to purge the air out of the lines.
It's important to keep a check on the propane tank and have it refilled before it gets empty.
For a whole house propane tank the pressure imbalances can sometimes lead to leaks when refilled and may lead to fires and explosions.
When a propane tank is empty it can also cause moisture and air to enter the tank and cause rust which can weaken the tank and cause leaks.
If you have pilot lights on furnaces, stoves etc they may not relight as good and take awhile to be lit again.
To avoid running out of propane in your home or business propane tank you should setup a regular delivery schedule where your propane dealer will deliver propane on a schedule to ensure you don't run out.
Also regularly check the propane tank fuel gauge and don't let the propane tank drop lower than 20 percent.
If you're using smaller propane tanks such as 20 lb to 100 lb bottles then running out of the propane in the tanks is not as big of a deal.
The appliances, grill etc will simply fail to light or the flame will go out.
You can then shut the propane tank valve off, disconnect the hose and take the propane tank to be refilled.
Then purge the air out of the line by turning on the valve and the appliance until you smell a bit of propane.
Then light the appliance.