An improperly used gas cylinder is a potential bullet or rocket. Have proper carts available for transporting gas cylinders. Do not roll large cylinders around. Use the proper tank and fittings designed for each gas. Your gas supplier will be able to help you with this.
Asphyxiation is the most subtle danger of working with compressed gases.
Always use compressed gases in a well-ventilated area. Always make sure tanks are secure. No compressed gas tank should be allowed to stand free. All tanks should be strapped or tightly chained to a rigid support to prevent accidental toppling. Keep electrical lines away from compressed gas tanks.