You can't get a scuba tank filled at most places without a cert card. As far as running air tools you will get about 10 minutes of use. I've used them underwater to drill holes in rock. For filling tires you will need a scuba regulator to reduce the pressure from 3000 psi to 125 psi. The scuba regulator has at least one High pressure port for the guage and two low pressure ports for the 2nd stage regulator that goes in your mouth. You want to use the Low pressure side and you can get a $10 adapter at most scuba shops for filling tires.

It's really only worth the effort if you scuba dive because you already have the tank and regulator. It is the fastest way to inflate tires but you have to be carefull the 125 psi will overinflate your tires in a heartbeat. Also Scuba tanks have to be visual inspected every year and hydrotested every 5. Scuba shops will not fill tanks without the inspection sticker. They kill people when they fail. There is a batch of bad aluminum ones made in the 80's that have the wrong alloy and every few years one pops and kills someone. Most other tanks will pop the burst disk first. You don't want to drop a 3000 psi tank <img src="/forums/images/graemlins/evil.gif" alt="" />