Methylene Chloride

Classification

Skin irritation, Category 2; Eye irritation, Category 2A; Carcinogenicity, Category 2; STOT single exposure, Category 3 (respiratory irritation, drowsiness or dizziness); STOT repeated exposure, Category 2 (central nervous system, liver, blood). Some suppliers also list low-level acute toxicity; check your SDS.

Hazard statements

• H315 Causes skin irritation.
• H319 Causes serious eye irritation.
• H335 May cause respiratory irritation.
• H336 May cause drowsiness or dizziness.
• H351 Suspected of causing cancer.
• H373 May cause damage to organs through prolonged or repeated exposure.

Key precautionary statements

• P201 Obtain special instructions before use.
• P260 Do not breathe vapors.
• P271 Use only outdoors or in a well-ventilated area.
• P280 Wear protective gloves, protective clothing, eye protection and face protection.
• P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing.
• P305+P351+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
• P308+P313 IF exposed or concerned: Get medical advice or attention.
• P403+P233 Store in a well-ventilated place. Keep container tightly closed.

Methylene chloride has its own OSHA standard (29 CFR 1910.1052, with matching rules for construction and shipyards). The PEL is 25 ppm as an 8-hour TWA and 125 ppm as a 15-minute STEL, with an action level of 12.5 ppm that triggers monitoring and medical surveillance. NIOSH treats it as a potential occupational carcinogen and recommends the lowest feasible exposure; the NIOSH IDLH is 2,300 ppm. The ACGIH TLV is 50 ppm TWA. Cal/OSHA matches the federal 25 ppm TWA and 125 ppm STEL. Skin contact adds to exposure even when air levels are low.

EPA's 2024 TSCA rule adds its own workplace exposure limits and monitoring requirements for the uses it still allows, and EPA has since extended some compliance dates. See the regulations section.

• Appearance: Colorless, very volatile liquid
• Odor: Sweet, chloroform-like odor; people quickly stop noticing it, so smell is not a reliable warning
• Molecular weight: 84.9
• Boiling point: 104°F (40°C)
• Freezing point: -139°F (-95°C)
• Flash point: None under normal test conditions; classed as a combustible liquid that is hard to ignite
• Autoignition temperature: About 1,033°F (556°C)
• Explosive limits: LEL 13%, UEL 23%
• Vapor pressure: 350 mmHg
• Vapor density: 2.9 (air = 1); vapors collect in low areas
• Specific gravity: 1.33 (sinks in water)
• Water solubility: 2%

Inhalation

Acts like an anesthetic. Causes headache, lightheadedness, nausea, confusion and drowsiness, and at high levels unconsciousness and death. Because it evaporates so fast and the vapor is heavy, dangerous levels build up quickly in pits, tanks, bathrooms and other confined or poorly ventilated spaces. The body breaks methylene chloride down into carbon monoxide, which reduces the blood's ability to carry oxygen and can strain the heart, especially in people with heart disease.

Skin

Irritates the skin. Liquid trapped against the skin by gloves, clothing or shoes can cause painful burns. It is absorbed through the skin.

Eyes

Splashes are painful and irritating and can damage the eyes; vapors also irritate.

Ingestion

Harmful if swallowed. Get medical attention immediately.

Target organs

Eyes, skin, cardiovascular system, central nervous system, liver

Long-term effects

Methylene chloride caused lung, liver and mammary tumors in animals. OSHA regulates it as a potential human carcinogen, NIOSH treats it as a potential occupational carcinogen, and NTP lists it as reasonably anticipated to be a human carcinogen. Repeated exposure may harm the liver, kidneys and nervous system (memory and coordination). Alcohol may increase liver effects.

Gloves

The New Jersey Department of Health lists polyvinyl alcohol (PVA) and Silver Shield/4H gloves, both with more than 8 hours of breakthrough time. Methylene chloride passes through many common glove materials quickly, so don't assume ordinary disposable gloves protect you. PVA breaks down in water. See hand protection. Avoid leather shoes, which absorb the liquid and cannot be cleaned.

Eyes and face

Chemical splash goggles and a face shield. The OSHA standard requires eyewash stations where eye contact with solutions containing 0.1% or more methylene chloride is possible.

Respiratory

Organic vapor cartridges are not effective for routine use. The OSHA standard requires atmosphere-supplying respirators (supplied-air or SCBA) and forbids half masks. Gas masks with organic vapor canisters are allowed only for emergency escape. Engineering controls such as local exhaust ventilation and substitution come first; see respiratory protection.

Clothing

Chemical-resistant clothing such as Tychem Responder or TK, or equivalent. Remove clothing that becomes wet or contaminated, and wash skin.

Store in tightly closed containers in a cool, dry, well-ventilated area away from heat, sunlight and metals. OSHA requires a marked regulated area wherever exposure exceeds, or can reasonably be expected to exceed, the PEL or STEL.

Never use methylene chloride-based strippers in enclosed spaces such as bathrooms, pits or tanks without forced ventilation and supplied air. Where possible, choose a safer substitute; the hierarchy of controls puts elimination and substitution first.

Keep away from

• Strong oxidizers (such as peroxides, perchlorates, permanganates, nitrates and chlorine)
• Chemically active metals such as aluminum, magnesium powder, sodium, potassium and titanium
• Strong bases such as sodium hydroxide and potassium hydroxide
• Concentrated nitric acid, liquid oxygen and amines
• Some plastics, rubbers and coatings; when wet, it corrodes iron, some stainless steels, copper and nickel

• Evacuate the area and keep people out; vapors build up quickly in low and enclosed spaces.
• Ventilate the area and eliminate ignition sources.
• Responders need supplied-air respirators or SCBA.
• Absorb with vermiculite, dry sand, earth or another inert material and place in sealed containers for disposal.
• Do not wash into sewers or drains.
• Waste is likely to be regulated as hazardous waste; check with your state environmental agency or EPA.
• For larger spills, refer to ERG Guide 160.

Suitable extinguishing media

• Dry chemical
• Carbon dioxide (CO₂)
• Foam
• Water spray to cool fire-exposed containers

Special hazards

Hard to ignite, but its vapor can burn at high concentrations and in the presence of strong ignition sources. In a fire or on hot surfaces it breaks down into highly toxic gases, including phosgene, hydrogen chloride (which forms hydrochloric acid with moisture) and carbon monoxide. Containers may rupture when heated. Firefighters should wear SCBA and full protective gear.

• OSHA Methylene Chloride standard (29 CFR 1910.1052; 29 CFR 1926.1152 for construction; the standard also covers shipyard employment): 25 ppm TWA, 125 ppm STEL, 12.5 ppm action level, with exposure monitoring, regulated areas, respirator rules and medical surveillance.
• OSHA Hazard Communication (29 CFR 1910.1200): Hazardous chemical; labels, safety data sheets and worker training required.
• EPA TSCA risk management rule (final rule published May 2024): Bans consumer uses and most industrial and commercial uses, including paint and coating removal. The remaining uses must follow a Workplace Chemical Protection Program with exposure monitoring. EPA extended some compliance dates in late 2025, so check EPA's methylene chloride page for current deadlines.
• CERCLA hazardous substance (40 CFR 302.4): Reportable quantity 1,000 lb (454 kg). RCRA waste code U080.
• DOT Hazardous Materials (49 CFR 172.101): UN1593 Dichloromethane, Class 6.1, PG III.

• NIOSH Pocket Guide: Methylene chloride
• OSHA Occupational Chemical Database: Methylene chloride
• OSHA 29 CFR 1910.1052: Methylene chloride
• OSHA 1910.1052 Appendix A: Substance Safety Data Sheet
• NJ Department of Health Hazardous Substance Fact Sheet: Methylene Chloride
• EPA: Risk Management for Methylene Chloride
• 40 CFR 302.4: CERCLA hazardous substances and reportable quantities