Quick Answer: Mono Ethylene Glycol (MEG, CAS 107-21-1, also labeled Ethylene Glycol/EG) is not highly flammable under normal storage and handling conditions. It is classified as a combustible liquid - it will not ignite at room temperature but can form a flammable vapor-air mixture once heated above its flash point of 111.11°C (232°F). For buyers and handlers, this means MEG carries a lower fire risk than low-flash-point solvents like ethanol or acetone, but it is not risk-free and still requires standard combustible-liquid storage practices.
Flammability of MEG: Key Data
MEG's flammability profile is defined by a comparatively high flash point, which is the main reason it is classified as combustible rather than highly flammable. Under global safety classification systems including NFPA 704 and GHS, MEG carries an NFPA flammability rating of 1 - meaning it must be preheated before ignition can occur, in contrast to a rating of 3 for highly flammable liquids such as acetone. The closed-cup flash point is 111.11°C (232°F) and the open-cup flash point is 115°C (239°F); the small gap between the two measurements indicates MEG has low volatility under normal ambient conditions, so it does not readily release flammable vapor at room temperature.
Ignition still requires substantial heat input even once the flash point is reached. MEG's autoignition temperature is 398–410°C (748–770°F), meaning the liquid will not self-ignite without an external ignition source unless exposed to extreme heat. Its explosive (flammable) range in air is 3.2%–15.3% by volume, so a flammable vapor-air mixture can only form once vapor concentration reaches this window - which, combined with MEG's low room-temperature vapor pressure of 0.06 mmHg, means meaningful vapor accumulation is unlikely under normal, unheated conditions. One practical handling note: MEG vapor is heavier than air, so if vapor is generated during a heating process, it can travel along floors or low-lying areas toward a distant ignition source rather than dispersing upward.
Fire Risks and Hazard Classification
MEG (CAS 107-21-1) is chemically stable under normal ambient conditions (20°C, 1 atm), and its fire risk is specifically tied to heating above its flash point rather than to routine storage or transport. Once heated past 111.11°C, MEG vapor can ignite on contact with open flame, sparks, or hot surfaces exceeding its autoignition temperature of roughly 398°C - a scenario more relevant to processing environments with heat sources than to ambient storage.
Reactivity is a secondary consideration alongside flammability. MEG reacts with strong oxidizing agents such as peroxides, nitrates, and permanganates, and contact with these materials raises both fire and reactivity risk independent of temperature. Separately from its fire profile, MEG is also toxic if ingested, with an oral LD50 of approximately 1.6 g/kg; ingestion can cause kidney damage, central nervous system depression, and metabolic acidosis, which is why handling protocols address toxicity exposure alongside flammability.
Safe Storage Guidelines
Storage temperature is the single most important control for managing MEG's fire risk, since keeping the liquid well below its flash point prevents flammable vapor from forming in the first place. MEG should be stored below 40°C - roughly 71°C under its flash point - and kept away from heat sources such as steam lines (which can exceed 150°C), direct sunlight, and open flame, all of which could otherwise drive localized temperatures toward the ignition threshold.
Container material and site layout also affect long-term storage safety. Suitable container materials include carbon steel, stainless steel 304/316L, aluminum, and PTFE-lined drums, chosen for their resistance to corrosion and leakage over extended storage periods. MEG should be stored separately from oxidizing agents, strong acids, and food or feed products, with a recommended minimum separation distance of 5 meters to limit cross-contamination or reaction risk in the event of a container failure. Spill containment systems sized to hold at least 110% of the largest stored container are standard practice for preventing spills from reaching drains or soil, and ventilation should be sufficient to keep vapor concentrations well below the 3.2% lower explosive limit (LEL) in any enclosed storage area. Restricting access to designated personnel further reduces the chance of accidental contact or mishandling.
Safe Handling and Fire Response
Standard combustible-liquid PPE - chemical-resistant gloves, splash goggles, and protective clothing - is the baseline control for handling MEG, since it limits skin and eye contact during transfer or sampling. Handling should take place in well-ventilated areas, with local exhaust ventilation providing enough air changes to keep vapor concentration well below flammable limits during any process that involves heating or open transfer. Eating, drinking, and smoking should be avoided during handling, and hands should be washed thoroughly after contact, since MEG can be absorbed through skin over time.
In a fire scenario involving MEG, alcohol-resistant foam, water spray, or dry chemical extinguishing agents are the appropriate response - a direct water jet should be avoided, as it can spread burning liquid rather than extinguish it. Combustion of MEG produces toxic gases including carbon monoxide, so self-contained breathing apparatus (SCBA) is required for any fire response in an enclosed or poorly ventilated space. Spill response should also prevent runoff into drains or waterways, since even limited quantities of MEG can cause environmental contamination if it reaches a water system.
FAQs
Is Mono Ethylene Glycol classified as a flammable or combustible liquid?
MEG is classified as a combustible liquid, not a highly flammable one. Its flash point of 111.11°C is well above room temperature, and it carries an NFPA 704 flammability rating of 1.
At what temperature does MEG become a fire risk?
MEG becomes a fire risk once heated above its closed-cup flash point of 111.11°C (232°F), at which point vapor can ignite if exposed to an ignition source.
What storage temperature is recommended for MEG?
MEG should be stored below 40°C - roughly 71°C below its flash point - to prevent vapor formation and minimize ignition risk.
What type of extinguisher should be used for a MEG fire?
Alcohol-resistant foam, water spray, or dry chemical extinguishers are appropriate. A direct water jet should be avoided, as it can spread the burning liquid.
Is Mono Ethylene Glycol dangerous if swallowed, even if it isn't highly flammable?
Yes. Separate from its fire profile, MEG has an oral LD50 of approximately 1.6 g/kg and can cause kidney damage, CNS depression, and metabolic acidosis if ingested - its fire safety classification does not reflect its toxicity risk.
Conclusion
Mono Ethylene Glycol is not highly flammable at room temperature, but it is a combustible liquid capable of forming flammable vapor once heated above 111.11°C, and its toxicity profile means handling protocols need to address both fire and health risk. Its comparatively high flash point makes it manageable for normal industrial storage and use, provided storage temperature, container material, ventilation, and separation from incompatible materials follow standard combustible-liquid practice. Always consult the current Safety Data Sheet (SDS) for the specific grade and region of the product being handled, since minor variations in formulation or regional regulation can affect specific handling requirements.