Mono Ethylene Glycol (MEG, also known as Ethylene Glycol, EG) is not highly flammable under normal conditions, but it is combustible and can form flammable vapor–air mixtures when heated above its flash point of 111.11°C (232°F).
Flammability of MEG: Key Data
MEG is classified as a combustible liquid under global safety standards such as NFPA 704 and GHS, meaning it does not ignite easily at room temperature but can ignite when sufficiently heated.
Flash point (closed cup) is 111.11°C (232°F), which confirms MEG requires high heating before it becomes flammable compared to low-flash-point solvents like ethanol.
Flash point (open cup) is 115°C (239°F), showing only a small difference from closed-cup measurement, which indicates low volatility under normal conditions.
Autoignition temperature is 398–410°C (748–770°F), meaning MEG requires extreme heat to ignite without an external flame.
Explosive limits in air are 3.2%–15.3% (vol), indicating flammable mixtures can form only under elevated temperature conditions.
NFPA 704 flammability rating is 1, meaning MEG must be preheated before ignition can occur, which is significantly lower than highly flammable liquids like acetone (rating 3).
At room temperature (20°C), MEG has a very low vapor pressure of 0.06 mmHg, which limits vapor release and reduces ignition risk in normal environments.
MEG vapors are heavier than air, with a density of 1.11 g/cm³ compared to air (~1.20 g/cm³), meaning vapor can travel to distant ignition sources when generated.
Fire Risks & Hazard Classification
Mono Ethylene Glycol (cas no 107-21-1) is stable under normal conditions (20°C, 1 atm) but becomes a fire risk when heated above its flash point of 111.11°C.
When heated above this temperature, MEG vapors can ignite if exposed to flames, sparks, or hot surfaces above 398°C.
MEG reacts with strong oxidizing agents such as peroxides, nitrates, and permanganates, which increases fire and reactivity risks.
MEG is toxic if ingested, with an oral LD50 of approximately 1.6 g/kg, and can cause kidney damage, central nervous system depression, and metabolic acidosis.
Safe Storage Guidelines
Proper storage significantly reduces fire and exposure risks.
MEG should be stored below 40°C, which is 71°C lower than its flash point, to prevent vapor formation and ignition risk.
Suitable container materials include carbon steel, stainless steel 304/316L, aluminum, and PTFE-lined drums, which provide high resistance to leakage and corrosion.
MEG must be kept away from heat sources such as steam pipes (which can exceed 150°C), sunlight, and open flames to prevent accidental heating above flash point.
It should be stored separately from oxidizing agents, strong acids, and food or feed products, with a minimum separation distance of 5 meters.
Storage areas should include spill containment systems capable of holding at least 110% of the largest container volume to prevent environmental contamination.
Ventilation should maintain vapor concentrations below 3.2% (vol), which is the lower explosive limit (LEL) of MEG.
Access should be restricted, as controlled storage areas reduce accidental exposure risks by up to 80%.
Safe Handling & Fire Response
Proper PPE such as chemical-resistant gloves, goggles, and protective clothing can reduce exposure risk by up to 99%.
Mono Ethylene Glycol MEG should be handled in well-ventilated areas with at least 10 air changes per hour to maintain vapor concentration well below flammable limits.
Avoid eating, drinking, or smoking during handling, and wash hands thoroughly after contact due to potential skin absorption within minutes.
For fire emergencies, alcohol-resistant foam, water spray, or dry chemical extinguishers should be used.
Direct water jet should be avoided as it may spread burning liquid and increase fire area significantly.
Burning MEG produces toxic gases such as carbon monoxide, requiring self-contained breathing apparatus (SCBA) for fire response.
Spill control should prevent runoff into drains or water systems, as even small quantities can cause environmental contamination.
Conclusion
Mono-ethylene glycol is not highly flammable at room temperature, but it is a combustible liquid that can form flammable vapor mixtures when heated above 111.11°C.
Its relatively high flash point makes it safe for normal industrial use, but strict storage and handling procedures are required to prevent fire, reactivity, and health risks.
Always refer to the latest Safety Data Sheet (SDS) for specific handling requirements, as safety data may vary slightly depending on grade and region.