SkunkPatronus: Very true and also a very good point. Sourcing the purest form of these gases can be tough but not impossible. For example, pure propane has no smell but all propane you buy from your gas station has a skunk oil added to it in order to allow you to detect a leak before something bad happens. It can be sourced though if you do some digging in your local area, same with butane. Chemical and scientific supply shops are a good place to start looking. If you wish to test the impurities of a can of store bought triple refined near 0 impurities butane you can do so with the following method.
Take a bowl and a scale accurate down to .01 g.
Weigh the bowl and record the results.
Spray the butane into the bowl.
Allow it to evaporate.
Weigh the bowl and record the results.
Minus the start weight from the end weight and this will give you the amount of impurities found in said can of butane.
We are exposed on a daily basis to many chemicals from petroleom products, materials used in the building of homes, materials used in the construction of roads, pesticides used to control bugs in the farmers field, heck even some of the things they spray our clothes with to stain guard them are dangerous but only at high enough levels. You intake mercury on a daily basis and don't even know it but you are still here.
True safety should be a concern and I would never suggest using cheaply produced butane containing many contaminents but for the most part you will be safe so long as you employ a little common sense.
Unfortunately with the hand holding fear based society people are being raised in common sense is becomming much more rare. (this is not a jab at you just the world in general as you seem to be intelligent).
There are plenty of heavy metals and bad stuff in the tap water we all drink but we are all still here, its all about being as safe as you can within reason.
Also the propellant used is inert and dissipates immediately upon release. You don't have to make BHO if you don't want to but I assure you when done properly it is perfectly safe and one of the most amazing smokes in the world.
I found all my pictures and will post a tutorial this afternoon after I get my "honey do's" done.