For reasons of safe transportation of fruits, mangoes, bananas etc are picked before they ripen fully. Slightly green harvested mangoes are subjected to small containers of calcium carbide (CaC2) with a plastic covering. CaC2 reacts with the moisture in the air to release acetylene (or ethyne) gas, which like ethyleneis - a chemical substance produced by fruits to accelerate the normal process of fruit maturation - is a ripening hormone. Industrial-grade calcium carbide contains arsenic and phosphorus, and its use for the purpose of ripening is illegal in many countries.