Many people have propane tanks that they freely use for a variety of applications. Some people hook them up to portable flame devices to do weeding or lawn work.
Some people choose to use them to heat the burners on a grill. One of the best uses for propane is using it to heat a home or a workspace either inside or outside.
The fear among many people when doing this is whether the propane tank could ignite and cause some sort of explosion. If that is possible, it certainly would not be worth the risk to use it inside.
Propane heaters produce a great deal of heat. They should not be left running constantly simply because they will probably provide too much heat; especially if they are placed in a small area.
These heaters are safe for indoor use. They are meant to be unattended but that does not mean that they do not require some supervision for safe use. You do not want to leave your home if you have a propane heater running, because anything could happen to it while you are gone. You have to make sure that there is adequate ventilation for the heater as well.
This is for two reasons. The first reason is that there has to be air circulating to allow for combustion with the heater. The second reason is that there has to be some way for the water vapor and carbon monoxide that is produced by the heater to escape from the area. It may be a wise choice to purchase a carbon monoxide detector to put into the house in order to help protect yourself from possible carbon monoxide poisoning.
In conclusion, it is safe to use indoor propane heaters. If you want, you can even use some of the smaller outdoor propane heaters indoors. Once again, you do not want to leave these alone for long periods of time without checking on them.
Having a highly flammable and combustible material around is dangerous enough without adding in a flame and a lack of supervision. This is a recipe for disaster.
The only real danger that exists (as long as the propane heater is under supervision) is the risk of carbon monoxide poisoning. Once again, however, this is not a risk if you simply purchase a cheap carbon monoxide protector to help keep you safe and alert you to danger.