Calcium carbide and fruit ripening: what the FSSAI ban says why technical carbide is unsafe near food, and the ethylene alternative

Calcium carbide has been used, illegally, to ripen mangoes, bananas and papayas because a lump wrapped with the fruit gives off acetylene as it meets moisture, and acetylene imitates the ethylene that fruit produces as it ripens. In India this is prohibited. Regulation 2.3.5 of the Food Safety and Standards (Prohibition and Restrictions on Sales) Regulations, 2011 bans the sale of fruit ripened this way, and the Food Safety and Standards Authority of India permits ethylene instead. As makers of acetylene from carbide, KIGL handles this material every day, and the reasons it must be kept away from food are plain from its chemistry.

The prohibition is short. Under regulation 2.3.5, no person shall sell, offer or expose for sale, or keep on their premises for sale, under any description, fruit that has been artificially ripened by acetylene, which the regulation describes as "commonly known as carbide gas". It applies to traders, wholesalers, retailers and every other food business operator, and enforcement lies with state food safety departments under the Food Safety and Standards Act, 2006.

Calcium carbide is an industrial chemical made by melting lime and coke in an electric furnace, as explained under what is calcium carbide. There is no refining step, so whatever phosphorus, sulphur and arsenic the raw materials bring stays in the product, and on contact with water those impurities come off with the acetylene as phosphine, hydrogen sulphide and arsine.

The Indian carbide standard shows how much is tolerated in industrial use. IS 1040:1987, clause 5.3, allows the gas from technical carbide to carry:

Those limits are written for a gas that goes into a welding torch after purification, not for an atmosphere around food or people. For comparison, NIOSH sets a recommended exposure limit for phosphine of 0.3 ppm as an 8-hour average, with an immediately-dangerous level of 50 ppm, and for arsine a 15-minute ceiling of 0.002 mg/m³, flagging arsine as a potential occupational carcinogen. Indian carbide has historically sat at the high end. Routine testing by British Oxygen Co. of carbide sold in Britain, by the method of BS 642:1951, found 150–310 vpm of phosphine in gas from 19 manufacturers in 12 countries, but 800–1,000 vpm at times in Indian carbide (unpublished BOC data, as compiled by S. A. Miller, 1965), as set out under phosphine in acetylene and Indian carbide. That survey dates from the 1950s and 1960s, but the chemistry has not changed.

FSSAI's own statements name arsenic and phosphorus as the harmful traces and list dizziness, frequent thirst, irritation, weakness, difficulty in swallowing, vomiting and skin ulcers among the effects. The guidance note adds that the acetylene released is harmful to the people handling the fruit.

There are two further practical problems:

• Residue. Carbide reacts to calcium hydroxide, a strong alkali, and powder or lime can be left on the skin of the fruit.
• Fire. Acetylene is flammable in air from 2.5 to 82 % (IS 14814:2023), and a closed godown or crate of fruit with carbide can build a flammable atmosphere; the hazards of carbide itself are covered in calcium carbide safety data.

Ethylene is the plant hormone that fruit produces naturally to start ripening, and FSSAI permits it as the ripening agent. The FSSAI Guidance Note on Artificial Ripening of Fruits sets out how:

The permitted sources are ethylene gas cylinders fed through a calibrated regulator, compressed ethylene in aerosol cans sprayed into the chamber space and not onto the fruit, ethylene generators such as catalytic converters working on ethanol, and ethephon (2-chloroethylphosphonic acid), either as 39 % SL formulation with an alkali or as powder in sachets. Ethephon 39 % SL is approved by the Central Insecticides Board and Registration Committee. Whatever the source, it must not touch the fruit: a sachet goes in a perforated box in the crate and comes out after about 24 hours, and it must not contain carbide or acetylene.

The ethylene limit of 2.7 % in the guidance is the gas's lower explosive limit, and 100 ppm is 0.01 %, so a properly run chamber operates at less than one two-hundredth of it. The rule that matters is the same as for any fuel gas: no smoking, no open flames, leak checks on the cylinder and regulator, and sound electrical fittings, all of which the guidance repeats.