fuel must be kept a minimum safe distance from any potential source of ignition.
For example, here are the figures for liquid oxygen and its minimum safe distance from various potential sources of ignition:
- Building structures
- Wood frame construction 50 ft
- Other than wood frame construction 1 ft
- Confining areas 75ft/35ft
- Wall openings 10 ft
All classes of flammable and combustible liquid storage
Below ground storage
- Horizontal: Distance between tanks 15 ft
- Distance between O2 and tank openings 25 ft
etc.
(source: http://www.airliquide.com/us/databook/)