The Locarno Treaties of 1925 lifted the restrictions on German airship construction, and the Zeppelin company started construction of the "Graf Zeppelin" (LZ 127), the largest airship that could be built in the company's existing shed, and intended to stimulate interest in passenger airships. The "Graf Zeppelin" burned "blau gas", similar to propane, stored in large gas bags below the hydrogen cells, as fuel. Since its density was similar to that of air, it avoided the weight change as fuel was used, and thus the need to valve hydrogen. The "Graf Zeppelin" had an impressive safety record, flying over (including the first circumnavigation of the globe by airship) without a single passenger injury.