The Bristol Breather is an inexpensive personal breathing and utility apparatus invented by the Bristol corporation for high altitude bombers. Coupled with a pressure suit and larger oxygen tanks, it has proven to be one of the factors that allowed for high altitude airship travel. There are four tank sizes: small, medium, large and huge. The latter two are standard issue in airship crews, because they can last up to 1 and 2 hours respectively. Oxygen is refilled at an oxygen generator station. Many utilities can be loaded on the platform carrying the tanks, such as working tools or bags.