Methyl chloride—aka chloromethane—is a clear, colourless, and highly flammable gas. It is a naturally occurring ubiquitous gas, that has a faint, but sweet odour. Its chemical formula is CH3CI. [1,2,3]
Methyl chloride is used across various industries. In the past it was used as a refrigerant and an anaesthetic. It is now used in the manufacture of silicone polymers, and as a methylating agent to attach CH3 to oxygen and nitrogen. Methyl chloride is also used as a solvent.
Routes of Exposure [4,5]
The primary route of exposure for methyl chloride is via inhalation.
Methyl chloride is made in the ocean by natural processes, meaning that it is present in the air all over the world. The outside air contains less than 1ppb of methyl chloride. Those who are most likely to be exposed to the chemical in the air are those who work in chemical plants where methyl chloride is being used.
Methyl chloride poisoning affects a range of systems including the integumentary and nervous systems.
Acute Effects 
Severity of symptoms depend on the level and type of exposure.
Acute methyl chloride poisoning can result in vomiting and convulsions, followed by an apparent recovery and then recurrence of these symptoms.
Other symptoms include: nausea, diarrhoea, abdominal pain.
Dermal exposure can cause irritation, vesiculation and erythema.
Dermal exposure to the liquid form of the chemical can result in frostbite.
Heavy, but acute poisoning can cause CNS depression, headaches, dizziness, weakness or paralysis, pulmonary oedema, drowsiness and a coma or death.
Chronic Effects 
Methyl chloride is toxic to multiple body systems. Long-term exposure to the chemical can result in blurred vision, confusion, numbness of extremities, ataxia, tremors, confusion and hallucinations. Symptoms of long-term poisoning can last several months.
First Aid Measures 
Ingestion: Ingestion is not considered a potential route of exposure. However, if this chemical is ingested, DO NOT INDUCE VOMITING, and immediately contact a medical professional.
- Skin contact: The liquid form of this chemical may cause frostbite. For exposure to the liquid form, warm frostbitten area with water that does not exceed 41°C. Maintain skin temperature for at least 15 minutes, or until normal look, touch and temperature have returned. If there is heavy exposure, remove clothing while showering with warm water. Immediately contact a healthcare professional.
- Eye contact: Rinse eyes carefully with water for at least 15 minutes, ensuring to hold both eyelids open so they are flushed thoroughly. Contact an ophthalmologist immediately.
- Inhalation: Take victim to the nearest fresh air source and monitor their breathing. If they are not breathing, and you are qualified, you can administer CPR—with a pocket mask or one-way valve. Immediately contact a medical professional.
- General: Never administer anything by mouth to an unconscious, exposed person.
Exposure Controls/Personal Protection 
Emergency eyewash fountains and safety showers should be accessible in the immediate area of the potential exposure. Ensure there is adequate ventilation. Only use in conjunction with an explosion-proof local exhaust system, e.g. a fume hood.
Safety glasses, protective and dustproof clothing, gloves, an apron and an appropriate mask. Follow the PPE guidelines set in your jurisdiction.
The Occupational Safety and Health Administration (OSHA) has set an 8-hour time weighted average (TWA) concentration limit for methyl chloride of 100ppm.
Safe Work Australia has set an 8-hour time TWA for ethyl chloride of 20ppm. They have set a Short Term Exposure Limit (STEL) of 80ppm.