Unless you've drowned the carpets in fire-retarding spray or something, yeah it's a fire hazard. So is 99% of the stuff you're surrounded by at any given time.
Back to the discussion, sound-proofing is only marginally related to sound-absorption, in that mass=good. To sound-proof a room (e.g., make sure you can't hear anything else in the house and nobody else can hear you) you need to do fun stuff like double-walls, which in many cases just isn't feasible. For sound-absorption, you need some heavy foam/fiberglass. Then there's other fun stuff like reducing the amount of parallel surfaces (e.g. walls/ceiling), reducing odd frequency canceling/doubling (bass traps and such), etc.
So basically, there's a whole sh*t-load of fun stuff you get to do to accomplish *everything* you want to do, but any little bit helps too
In your case, I'd follow the advice you've gotten already and build some dense-fiberglass wall-hanging things, and put them on your walls, especially in corners. Another option is to build movable walls out of things like office cubicle dividers, some 2x4's, and some casters, and place them around whatever's being loud at the time. (although a completely dead room isn't good for drums either!)