What is the lethal substance used in coal mining called?

Answer 1

Where did you get that they use a lethal substance to mine coal?
They don't use lethal substances - with the inherent dangers of coal mining that would be just plain silly. Coal is mined by either strip mining (taking the coal out of the surface by removing the soil) or underground mining (digging tunnels and removing the coal as they tunnel.

But maybe you just worded your question wrong.

Maybe you meant what lethal substance is found in coal mining?
Methane, carbon dioxide, carbon monoxide, and sulfur gases are all dangerous and can build up in underground mines to lethal levels.

Answer 2

Gelignite.

The miners drill correctly-spaced holes into the coal face, and insert sticks of gelignite and detonators. They go far enough away to be safe, and fire the detonators, so the gelignite explodes and fractures the entire exposed face of the coal seam. Then the miners return and shovel the loose coal into trucks. They can do this several times in each shift.

The gelignite is lethal because if the miners were too close when it exploded, they would be killed.

Answer 3

Coal dust isn't good for you. Methane gas can cause explosions, carbon dioxide can suffocate you. Water in coal mines can drown you. Take your pick.