330 Economics
333 Economics of land and energy
333.7 Land, recreational and wilderness areas, energy
333.79 Energy
333.791 General topics of energy
333.792 Primary forms of energy
333.793 Secondary forms of energy
333.8 Subsurface resources
333.9 Other natural resources
621 Applied physics
621.042 Energy engineering
621.47 Solar-energy engineering
621.48 Nuclear engineering
622 Mining and related operations
662 Technology of explosives, fuels, related products
662.6 Fuels