Minimum duration of developing coal minor pneumoconiasis is –
Coal worker pneumoconiosis (Antracosis) 

There are two general phases in coal miners pneumoconiosis


The first phase : Simple pneumoconiosis : This is associates with only little ventilatory impairment but requires 12 years of work exposure for its development.
The second phase : Progressive massive fibrosis : This is associated with severe respiratory disability and takes much longer.
2–4 years
4–6 years
8–10 years
More than 10 years