The following message is intended for any lab workers using chloroform.  The source is the Occupational Safety unit of Lockheed Martin Idaho Technologies Company which operates a national lab in Idaho.  Please be certain that all lab workers using chloroform in your unit or facility are aware of this important issue.

Title: YELLOW - Phosgene Generated from Chloroform

Identifier: INEEL Lessons Learned # 98247
Date: May 25,1998

Lessons Learned Statement:

Phosgene can be generated from chloroform.  Chloroform stabilized with alcohol should be purchased, and the chemical should be treated as time-sensitive.  An industrial hygienist should be contacted before using a container of chloroform that is six months old or older.

Discussion of Activities:

Researchers at the University of California, Los Angeles were using a three-year-old bottle of chloroform.  They noticed that the people working with the chloroform were becoming quite ill.  Subsequent analysis showed concentrations of 15,000 ppm of phosgene in the head space of the bottle and a 1.1% concentration of phosgene in the bulk solution.  Exposure to 20 ppm for 1-2 minutes can cause severe lung injury and 570 ppm for 1 minute can cause death.  The chloroform was stored properly and was stabilized with amylene. (Note: Chloroform comes in three basic varieties: a) no stabilizer present, b) stabilized with amylene, and c) stabilized with an alcohol such as ethanol.)

A search of the literature has shown that the generation of phosgene from chloroform was a well-known phenomenon 50-100 years ago when chloroform was used as an anesthetic.  Evidently, the generation of phosgene from chloroform has since been forgotten since there are no warnings on material safety data sheets for chloroform, including chloroform that has not been stabilized.

Recommended Actions:

1. Unless program requirements prohibit it, chloroform that is stabilized with alcohol should be purchased in the future.  Alcohol is usually added in greater concentrations than amylene so it provides better protection from phosgene generation.  Also, there is evidence that amylene may not prevent phosgene generation.

2.  Chloroform should be treated as a time-sensitive chemical.  This is especially true of chloroform that is either not stabilized or is stabilized with amylene.

3.  An industrial hygienist should be contacted before using a container of chloroform that is six months old or older so that they can test for the presence of phosgene.

References: Chemical & Engineering News, March 2, 1998

Chloroform should always be stored in a dark place.  The 1995 edition of Prudent Practices in the Laboratory  states (p. 283): "In the presence of light, chloroform undergoes autoxidation to generate phosgene; this can be minimized by storing this substance in the dark under nitrogen.  Commercial samples of chloroform frequently contain 0.5 to 1% ethanol as a stabilizer."

There is a fairly easy test for phosgene using a home made test paper.

"Paper soaked in alcoholic solution containing 10% of a mixture of equal parts of p-dimethylaminobenzaldehyde and colorless diphenyamine, then dried, will turn from yellow to deep orange in the presence of approximately the maximum allowable concentration of phosgene."  The permissible exposure limit for phosgene is 0.1 parts per million (p.p.m.), so this is a fairly sensitive test.  This test paper is faily inexpensive to make:
 p-dimethylaminobenzaldehyde --Sigma # D 2004; 25 g., $8.85; diphenyamine--Sigma # D 2385; 5 g., $13.50, 25 g. $50.35.

It is recommended that anyone using chloroform test their available supplies before using them again, especially if the chloroform bottle has been open for more than three months.  This procedure must be conducted in a fume hood while double gloving with heavier weight disposable nitrile gloves or viton gloves.  Hold the test paper near the mouth of the container as it is opened to see if there is any phosgene in the head space of the container.  If phosgene is detected is is not advisable to continue using the material.  Label the container with an Cornell EH&S waste label, noting that the chloroform is contaminated with phosgene, and make arrangements for it to be disposed of as hazardous waste. Note that chloroform is a listed hazardous waste and that it is highly illegal to dispose of chloroform by allowing it to evaporate in a fume hood as this is considered an illegal release of a hazardous waste to the environment, the air in this case. It may be possible for a skilled chemist to remove the phosgene from the solution with chloroform and then redistill the chloroform, but this is not recommended.  If you have any questions concerning these procedures please feel free to contact me at 255-8849.

Chloroform is only moderately toxic, but it is an irritant, a narcotic, a heptotoxin, a nephrotoxin and it is a listed carcinogen.  The permissible exposure limit for chloroform 2 p.p.m.  The odor threshold is 200 p.p.m. for most people.  If you can smell chloroform when you are using it, there is a good chance are you are being overexposed.  Since it is a listed human carcinogen, it is recommended that it be handled in a manner which will reduce exposures to as low as reasonably achievable (ALARA).  It should always  be used in a fume hood, with the appropriate personal protective equipment.  I have seen quite a bit of benchtop use of chloroform and this is not good practice.  Also, any significant  use of chloroform requires a written standard operating procedure per the Lab Standard and the Chemical Hygiene Plan.

If you have chloroform in your lab and you are not actively using this material, it would be wise to have it taken away as hazardous waste.  If you do need chloroform for a protocol in use, stock only what you can use in three months or less.  Set up a "just-in-time" purchasing policy and purchase the smallest container size that is practical.  Keep waste bottles tightly capped and stored in a ventilated storage cabinet or, at last resort, in a fume  hood.   It would also be good to look for a less hazardous substitute for chloroform, if possible.