Patent classifications
E
FIXED CONSTRUCTIONS
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E21
EARTH OR ROCK DRILLING; MINING
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E21F
SAFETY DEVICES, TRANSPORT, FILLING-UP, RESCUE, VENTILATION, OR DRAINING IN OR OF MINES OR TUNNELS
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17/00
Methods or devices for use in mines or tunnels, not covered elsewhere
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E21F17/18
Special adaptations of signalling or alarm devices
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