Self-Contained Breathing Apparatus (SCBA): Firefighters and emergency service workers use full face masks that provide breathing air as well as eye and face protection. These masks are typically attached to a tank carried upon the back of the wearer and are called self-contained breathing apparatuses (SCBA). Because oxygen breathing is hazardous in areas where fires may be burning, and because open-circuit compressed-air breathing sets are easier to refill than rebreathers, SCBA units are normally filled with compressed breathing air rather than oxygen. Specialized full-face masks that supply oxygen or other breathing gases are used by divers and astronauts to remove nitrogen from their blood before space walks (EVA) or underwater decompression. Anesthesia oxygen masks: Anesthesia masks are face masks that are designed to administer anesthetic gases to a patient through inhalation. Anesthesia masks are either made of anti-static silicone or rubber, as a static electricity spark may ignite some anesthetic gases. They are either black rubber or clear silicone. Anesthesia masks fit over the mouth and nose and have a double hose system. One hose carries inhaled anesthetic gas to the mask and the other brings exhaled anesthetic gas back to the machine. Anesthesia masks have 4 point head strap harnesses to securely fit on the head to hold the mask in place as the anaethesia doctor controls the gases and oxygen inhaled