<Tr> <Th> RTECS </Th> <Td> MW8900000 </Td> </Tr> <Tr> <Th> PEL - OSHA </Th> <Td> Simple asphyxiant </Td> </Tr> <Tr> <Th> ACGIH TLV - TWA </Th> <Td> Simple asphyxiant </Td> </Tr> <P> Liquid hydrogen can be used as the fuel for an internal combustion engine or fuel cell . Various submarines (Type 212 submarine, Type 214 submarine) and concept hydrogen vehicles have been built using this form of hydrogen (see DeepC, BMW H2R). Due to its similarity, builders can sometimes modify and share equipment with systems designed for liquefied natural gas (LNG). However, because of the lower volumetric energy, the hydrogen volumes needed for combustion are large . Unless direct injection is used, a severe gas - displacement effect also hampers maximum breathing and increases pumping losses . </P>

Where is hydrogen found and how is it obtained