Allyl chloride

Allyl chloride (3-chloropropene) was first synthesized in the 1940s and became important industrially as a precursor to glycerol, epichlorohydrin, and allyl esters used in resins and adhesives. [1] It is produced by high-temperature chlorination of propylene and is a high-volume chemical (hundreds of millions of pounds per year in the US). The primary end use is as an intermediate in epichlorohydrin production, which in turn feeds epoxy resin and synthetic glycerol manufacturing. Allyl chloride has a recognizable garlic- or onion-like odor, but this odor may not provide adequate warning at concentrations that can cause harm — the odor threshold overlaps with exposure levels of concern. In industrial settings, exposure has caused peripheral neuropathy in workers — a pattern of numbness, tingling, and weakness in the extremities from damage to peripheral nerve axons. [2] Animal studies have shown hepatotoxicity (liver damage), kidney effects, and reproductive toxicity. The EPA includes it on the HAP list and the NIOSH REL is 1 ppm (TWA) and 3 ppm (ceiling). The compound is also reactive and flammable (boiling point 45°C), creating fire hazard in addition to health hazard at production facilities. [3]

Chemical plant workers manufacturing allyl chloride or using it to produce epichlorohydrin, allyl esters, and other derivatives are the main occupationally exposed population. Inhalation of vapors is the primary route; skin absorption of the liquid also occurs. Environmental releases from chemical plants can contaminate local air. The general public has negligible exposures.

Peripheral neuropathy from allyl chloride exposure — documented in clinical case series from chemical plant incidents — involves sensory and motor nerve damage that can be partially or fully reversible after cessation of exposure if caught early, but can become permanent with continued high-level exposure. [2] Hepatotoxicity (elevated liver enzymes, histopathological changes) occurs at moderately high occupational exposures. Allyl chloride is also acutely irritating to the eyes, nose, and throat, and pulmonary edema can result from extremely high inhalation exposures. Reproductive effects (reduced fertility in male rats) are another concern.

Chemical plant workers in allyl chloride, epichlorohydrin, and allyl ester manufacturing facilities face the primary occupational risks. Workers in countries with less stringent industrial hygiene controls face the highest actual exposures.

1. Continuous air monitoring is essential given inadequate odor warning — personal samplers set at the NIOSH REL action level. 2. Local exhaust ventilation and enclosed process equipment minimize vapor generation. 3. Chemical-resistant gloves (neoprene or butyl rubber) and face/eye protection required for all liquid handling. 4. Any worker with tingling, numbness, or weakness in hands or feet should be removed from allyl chloride exposure immediately and referred for neurological evaluation. 5. Regular nerve conduction velocity testing for workers with significant repeated exposures.