It's not possible unless you're actually trying to light it on fire (ie. shooting your GBB in a small confined area and smoking at the same time). And even then it's probably going to be hard unless you're deliberately trying to do it. Only a small amount of propane is actually expelled, not really enough to catch fire and plus the valve that outputs propane is only depressed for a short period of time and when the slide goes back forward the knocker stops pressing on the valve.
So no the concerns aren't warranted.
PS: Green Gas = Propane so switching to green gas won't prevent the "off chance" of it blowing up in your face.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE