Pressure regulators are used with Diving cylinders for Scuba diving. The tank may contain pressures in excess of , which could cause a fatal barotrauma injury to a person breathing it directly. A demand controlled regulator provides a flow of breathing gas at the ambient pressure (which varies by depth in the water). Pressure reducing regulators are also use to supply breathing gas to surface-supplied divers, and people who use self-contained breathing apparatus for rescue and hazmat work on land. Supplementary oxygen for high altitude flight in unpressurised aircraft and medical gases are also dispensed through pressure reducing regulators from high-pressure storage.