Editing Liquid rocket propellant (section)

===Comparison to kerosene===
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Launch pad fires due to spilled kerosene are more damaging than hydrogen fires, for two main reasons:
*Kerosene burns about 20% hotter in absolute temperature than hydrogen.
*Hydrogen's buoyancy. Since hydrogen is a deep cryogen it boils quickly and rises, due to its very low density as a gas. Even when hydrogen burns, the [[Steam|gaseous {{chem|H|2|O}}]] that is formed has a molecular weight of only 18&nbsp;[[Atomic mass unit|{{sc|amu}}]] compared to 29.9&nbsp;[[Atomic mass unit|{{sc|amu}}]] for air, so it also rises quickly. Spilled kerosene fuel, on the other hand, falls to the ground and if ignited can burn for hours when spilled in large quantities.
Kerosene fires unavoidably cause extensive heat damage that requires time-consuming repairs and rebuilding. This is most frequently experienced by test stand crews involved with firings of large, unproven rocket engines.

Hydrogen-fuelled engines require special design, such as running propellant lines horizontally, so that no "traps" form in the lines, which would cause pipe ruptures due to boiling in confined spaces. (The same caution applies to other cryogens such as liquid oxygen and [[liquid natural gas]] (LNG).) Liquid hydrogen fuel has an excellent safety record and performance that is well above all other practical chemical rocket propellants.