I cannot see the volume of HFC134a in a can of duster being enough to pose a risk in an enclosed basement. Even if you dumped the whole can at once, I cannot see it causing any side effects. All the gas is doing to kids that get "high" on it is replacing oxygen in the blood stream, causing a mild buzz thats really the brain lacking good ole O2. They're starving the brain of oxygen to get high, its really fucking smart of them. Not to mention the brain freeze they must get from the cold dry gas.
For us GBB owners, I really do not think we have anything to worry about, so far as health risks. I fire my GBB's indoors mostly, and while I notice an odour from the gas, I have never once noticed any side effects from it.
Kids will sniff anything to get high it seems. Gasoline, weed killer, insecticide, model glue, super glue, epoxy, spray paint.. fuck, if it emits fumes, kids will sniff it. Not all kids, but some really bloody dumb ones.