BB-H-886E
6.4 Basis of purchase. The basis of purchase should be the cubic foot, based upon normal
atmospheric conditions. Hydrogen is commercially available in cylinders of various rated
capacities, with capacities of approximately 200 and 300 cubic feet being common. The quantity
in cubic feet for each cylinder size is provided in the characteristics data of the applicable stock
number. Normally, hydrogen cylinders will be filled to the following standard conditions: 1800,
2000, 2265, or 2400 pounds per square inch gauge (psig) at 70 F (21.1 ºC). In cases where the
only cylinder available is rated for a higher pressure than requested, Department of
Transportation regulations allow for cylinders to be filled to less than the marked service
pressure. Also, cylinders specially qualified under 49 CFR to bear the plus (+) mark, have been
approved for special filling limits up to 10 percent above the marked service pressure.
6.5 Subject term (key word) listing.
Balloon, meteorological
Cutting
Cylinder
Gas chromatograph
Lifting medium
Valve
Welding
6.6 Safety considerations. Hydrogen has a very wide flammability range of 4 to 74 percent in
air, and burns with an almost invisible flame. The following applies to gaseous hydrogen:
a. Opening a hydrogen cylinder valve to remove dirt or dust may cause self-ignition.
b. Using hydrogen from a cylinder without using a suitable pressure regulator is
hazardous.
c. Hydrogen has a very low ignition energy and can be ignited by static electricity.
d. Hydrogen heats when expanded and may self-ignite.
e. By displacing the oxygen in air, hydrogen can act as an asphyxiant.
f. Hydrogen, being very light, may accumulate in high spots if there is inadequate
ventilation.
6.7 Changes from previous issue. Asterisks (or vertical lines) are not used in this revision to
identify changes with respect to the previous issue due to the extensive changes.
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