Siderosis is a special form of pneumoconiosis caused by inhaling iron dust over long periods of time. The disease is seen in metal polishers, ochre workers and arc-welders and above all among iron miners. Siderosis is observed only after long exposure to heavy quantities of dust. Sixty percent of miners with siderosis have been exposed for 25 years or more. Probably not more than 5% of all miners are so affected.