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Chloroform, though dangerous on its own due to toxicity and carcinogenicity concerns, can form dangerous phosgene over time.
Phosgene (COCl2) is a toxic gas/liquid used as a chemical warfare agent during WWI. Phosgene can form in chloroform as it is exposed to oxygen and amounts of UV light (although UV light is not always necessary if catalytic contaminants are present). Phosgene has a characteristic odor of cut hay.
Phosgene is very toxic, with fatality occurring with short exposures of 50ppm and exposures of less than one minute at the 500ppm level. Persons exposed to phosgene may feel no adverse effects immediately, but may later suffer from pulmonary edema (build-up of fluid in the lungs) and possibly death up to 24 hours later.
Due to dangers from phosgene as well as the inherent dangers from chloroform itself, chloroform bottles should always be opened and dispensed in the hood. Persons using chloroform should also utilize gloves and eye protection at all times. If any cut-hay or similar smell is detected when using chloroform or any other chlorinated solvent, the incident should be reported and the individuals involved should seek medical attention.
Every bottle of chloroform should be treated as if it contains phosgene to help prevent exposure, however, testing is possible using test strips or sampling tubes. Testing can be done by the Chemical Hygiene Officer or can be done by the user using strips prepared as stated:
Strips of filter paper are dipped in 5% w/v Diphenylamine and 5% w/v Dimethylaminobenzaldehyde in an alcoholic solution (ethanol works fine) and then allowed to dry. Strips should be a very light yellow when dry, and activate to a dark yellow/orange color upon presence of phosgene.
Phosgene contaminated chloroform should not be used, and should be segregated and marked for waste disposal.