If there is any kind of popping or sizzle there is still butane in it and it can be harmful to smoke because its like smoking poison. If there is purge it a while longer. Preferably in a vac but just heat can work.
Butane is really not that toxic...Its the mercapthan added to butane/propane that is much more toxic.
This is copied from skunkpharms.
After removal from the crude oil, the gases are typically de-sulfurized using steam and a catalytic reactive bed, and fractionally distilled into the four basic gases. As fractional distilling separates the gasses by specific gravity, the principal contaminants in n-Butane at that point, will be Iso-Butane, a branched molecule isomer of n-Butane, as well as n-Propane, and Cyclo-Propane, plus low levels of heavier, longer oleaginous alkane wax chains.
Neither of the butanes or propanes are particularly toxic at any sort of reasonable levels. The following for instance is taken from a typical MSDS sheet for n-Butane. The Rat LD-50 (50% dead) is 658000 mg/m3 4 hours. That is breathing a 65.8% pure butane atmosphere and asphixiating.