Look at this miner, he is carrying at least 40 kg of coal. He has to walk up a narrow shaft underground, walk a kilometer to a weight station. The more he carries, the more he gets paid. How much? Around $0.20 a trip. From an occupational health perspective, he will develop a "black lungs" disease very soon.
Coal is a very heavy material. He is carrying a very heavy load as he walks up the slope. One minor "slip and fall" can be severe or even fatal.
No respiratory protection in use at all. He will develop the "black lungs" disease very soon, if he is not killed in a mining accident.
Smoking will speed up the progress of "blakc lungs" disease. However, smoking is a very common habit.