How Dangerous is Methylene Chloride?

Methylene chloride, also known as dichloromethane or DCM, may not be as dangerous as other chlorohydrocarbons – but it still poses some risks. For instance, it can irritate the skin and the mucous membranes of the lungs. It can also cause nausea, dizziness, headaches, and loss of consciousness if you’re overexposed to it.

As a liquid, it doesn’t have a flashpoint, but the vapour-air mixture can become flammable at 100°C or higher. It also has a very high autoignition temperature at 556°C. This means that it’s safe to store at room temperature and isn’t easily ignited, unlike other volatile substances. With all that in mind, the overall risks of methylene chloride as they relate to health and fire hazards are relatively low.

Is Methylene Chloride Safe?

The safety of any substance depends on various factors, such as quantity and environmental conditions like temperature – and also how you handle hazardous chemicals. For example, flour can explode when there’s a high quantity of flour dust and an ignition source. Even water is potentially hazardous when taken in excessive amounts. Similarly, methylene chloride is only safe in certain amounts and at specific conditions. 

According to peer-reviewed published studies, methylene chloride has the following lethal doses in laboratory animals:

  • Guinea pig: 5000 ppm, 2h
  • Rabbit: 10,000 ppm, 7h
  • Cat: 12,295 ppm, 4.5h
  • Dog: 14,108 ppm, 7h

DCM is a highly volatile substance with a vapour pressure of 46.5 kPa at 25 °C under 1 atm pressure. The substance is at its most hazardous when in vapour form. This is because when inhaled, it’s easily absorbed by the body and gets metabolised into carbon monoxide, which can lead to carbon monoxide poisoning.

On the other hand, the association of dichloromethane with cancers in humans, including those who are exposed to the chemical at work, is inconclusive. There’s not enough statistical data to support any significant link between occupational exposure to DCM and cancer development.

Despite the lack of evidence directly linking methylene chloride to cancers in humans, all necessary precautions should be taken when handling this chemical. Workers must wear PPE, including gloves, respirators, and boots. You must also avoid inhaling the vapours or letting your skin come in contact with the chemical. This is because methylene chloride can dissolve the fatty tissues of the skin, resulting in chemical burns.

One of the main applications of methylene chloride in the food industry is its role as a solvent in decaffeinating coffee beans. While this may sound like a huge health concern, DCM is almost entirely removed when the beans are roasted. In fact, most decaffeinated coffee products contain less than one part per million residual amount of the chemical, while the legal limit set by health and food regulation agencies is 10 parts per million.

The biggest danger of methylene chloride is that it’s metabolised into carbon monoxide in the body

Is Methylene Chloride Flammable?

Methylene chloride is only flammable at very high temperatures. As we’ve mentioned, it has an autoignition temperature of 556°C and at 1 atm of pressure. It doesn’t have a flashpoint, but can form a vapour-air mixture that is potentially flammable at above 100°C. 

By comparison, kerosene has a flashpoint of 38°C and gasoline has a flashpoint of −40°C. Since dichloromethane isn’t flammable at room temperature, it can be safely stored in large quantities at a laboratory or factory.

Is Methylene Chloride Banned in the UK?

The UK was a member of the European Union (EU) until 2020, and during this period, many regulatory provisions pertaining to trade and commerce were adopted by the UK from the EU. One of these regulations, which is still in effect today, bans the use of methylene chloride in paint strippers.

However, the ban is not absolute. Paint strippers that contain the substance are still allowed to be used in industrial settings. Professionals who use paint strippers containing DCM are also allowed to use the product, but they’re subject to some restrictions.

Member states of the EU have some leeway when it comes to allowing professionals to use paint strippers which contain methylene chloride. Currently, the UK still enforces the ban of the product for the general public.

What Are the Effects of Methylene Chloride?

Methylene chloride is most dangerous when inhaled as vapour. It can easily be absorbed by the body through the alveoli of the lungs. It will then be slowly metabolised as carbon monoxide. Some of the common symptoms of acute exposure to methylene chloride are:

  • Drowsiness
  • Dizziness
  • Numbness and tingling limbs
  • Nausea
  • Fatigue
  • Headaches
  • Irritation of the upper respiratory tract

In severe cases, it can lead to suffocation, loss of consciousness, coma, and ultimately death. Most of these symptoms are the same symptoms associated with carbon monoxide poisoning.
In humans, a vapour concentration level of between 8,000 and 20,000 parts per million can cause narcosis if the exposure time is between half an hour and four hours. Exposure to higher concentrations of above 50,000 parts per million can be life threatening.

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