Have you noticed that half the label on most cans of Duster are used for safety warnings?
It's mind blowing that a product designed to simply blow away dust would need to use toxic or flammable gases, especially when there are plenty of safe alternatives out there.
For example, I have a couple of small dusters from Giotto that don't have anything in them at all. You simply squeeze them and you get just enough air to clean most keyboards and camera lenses. They never run out, and they're completely safe.
I've also seen air cans that you can refill using a bicycle pump, and others that use plain carbon dioxide, which is neither flammable or toxic.