Yes, glycol is flammable under certain conditions. While glycols are generally considered combustible rather than highly flammable, they can ignite when exposed to sufficient heat, open flames, or ignition sources at elevated temperatures. The flammability characteristics of different types of glycols vary significantly, with some being more combustible than others. 

Understanding Glycol Flammability 

Glycols are classified as combustible liquids rather than flammable liquids because they require preheating before ignition can occur. The key distinction is that flammable liquids ignite easily at room temperature, while combustible liquids need to be heated to their flash point temperature before they can catch fire. 

Flash Points and Ignition Temperatures 

The flash point is the lowest temperature at which a liquid can form an ignitable mixture with air. Different glycols have varying flash points: 

  • Ethylene Glycol: 111-127°C (232-260°F) 
  • Propylene Glycol: 103°C (217°F) 
  • Diethylene Glycol: 124-147°C (255-297°F) 
  • Triethylene Glycol: 177°C (351°F) 
  • Polyethylene Glycol: 182-287°C (360-549°F) 
  • Butylene Glycol: 93°C (199°F) 

 

Types of Glycols and Their Flammability Characteristics 

  1. Ethylene Glycol

Ethylene glycol is combustible with a flash point of approximately 111°C (232°F). It has explosive limits of 3.2-15.3% by volume in air. When heated, it can form explosive vapor-air mixtures and produce toxic gases during combustion. The National Fire Protection Association (NFPA) classifies it with a flammability rating of 1, meaning it “must be preheated before ignition can occur”. 

  1. Propylene Glycol

Propylene glycol is combustible with a flash point of 103°C (217°F). It has explosive limits of 2.6-12.5% by volume. While it presents fire hazards, it is considered safer than ethylene glycol due to its lower toxicity. The NFPA also rates it with a flammability rating of 1. 

  1. Diethylene Glycol

Diethylene glycol is combustible with a flash point ranging from 124-147°C. It has explosive limits of 1.3-13.5% by volume. Like other glycols, it requires preheating before ignition can occur. 

  1. Triethylene Glycol

Triethylene glycol is combustible with a higher flash point of 177°C (351°F). It has explosive limits of 0.9-9.2% by volume. While it is flammable in liquid form, it is difficult to ignite. However, its vapors can form highly flammable and explosive vapor-air mixtures. 

  1. Polyethylene Glycol (PEG)

Polyethylene glycol is combustible with flash points ranging from 182-287°C, depending on molecular weight. It may burn, but it does not ignite readily. Higher molecular weight PEGs have higher flash points. 

  1. Butylene Glycol

Butylene glycol is combustible with a flash point of 93°C (199°F). Above this temperature, explosive vapor-air mixtures may form. It has a relatively low flash point compared to other glycols. 

 

Fire Hazards and Safety Considerations 

  1. Combustion Products

When glycols burn, they produce hazardous combustion products including: 

  • Carbon monoxide (CO) 
  • Carbon dioxide (CO₂) 
  • Toxic organic compounds 
  • Formaldehyde and other carbonyl compounds 

 

  1. Vapor Behavior

Glycol vapors are heavier than air and will collect in low-lying areas such as basements, confined spaces, and poorly ventilated areas. This creates additional fire hazards as vapors can travel along floors and ignite at distant ignition sources. 

 

  1. Fire Protection Systems Concerns

A significant safety concern has emerged regarding the use of glycol-based antifreeze solutions in fire sprinkler systems. Research by the National Fire Protection Association (NFPA) found that high concentrations of glycol antifreeze can actually intensify fires when discharged from sprinklers. The NFPA now limits antifreeze concentrations to: 

  • Maximum 40% propylene glycol by volume 
  • Maximum 50% glycerin by volume 
  • For new installations: Maximum 38% propylene glycol or 48% glycerin 

 

  1. Safe Handling and Storage Guidelines

Personal Protective Equipment 

When handling glycols, proper safety measures include: 

  • Wearing appropriate protective gloves (nitrile, chloroprene, or butyl rubber) 
  • Using safety goggles or face shields 
  • Wearing protective clothing to prevent skin contact 
  • Using respiratory protection in poorly ventilated areas 

Storage Requirements 

Proper glycol storage involves: 

  • Using compatible containers (stainless steel or high-density polyethylene) 
  • Storing in cool, dry, well-ventilated areas 
  • Keeping away from heat sources and ignition sources 
  • Maintaining temperatures below 40°C to prevent degradation 
  • Using tightly sealed containers to prevent contamination 
  • Separating from strong oxidizing agents and acids 

 

  1. Fire Prevention Measures

To prevent glycol fires: 

  • Eliminate ignition sources in storage and handling areas 
  • Ensure adequate ventilation to prevent vapor accumulation 
  • Use explosion-proof electrical equipment in areas with glycol vapors 
  • Implement proper grounding and bonding procedures 
  • Install appropriate fire detection and suppression systems 

 

  1. Fire Suppression Methods

Recommended Extinguishing Agents 

For glycol fires, appropriate extinguishing agents include: 

  • Alcohol-resistant foam (most effective) 
  • Dry chemical powder 
  • Carbon dioxide (CO₂) 
  • Water spray or fog (for cooling) 

Agents to Avoid 

Do not use: 

  • Solid water streams (can spread the fire) 
  • Regular foam (glycols can break down standard foam) 

Fire Fighting Precautions 

When fighting glycol fires: 

  • Approach from upwind positions 
  • Use a self-contained breathing apparatus (SCBA) 
  • Cool exposed containers with water spray 
  • Prevent runoff from entering sewers or waterways 
  • Be prepared for a potential container explosion due to heat buildup 

 

Environmental and Regulatory Considerations 

  1. Environmental Impact

Glycol spills and fire runoff can cause environmental damage: 

  • Prevent entry into drains, sewers, and water bodies 
  • Use containment barriers to control spills 
  • Follow proper disposal procedures for contaminated materials 
  • Report spills according to regulatory requirements 

 

  1. Regulatory Compliance

Various regulations govern glycol handling and storage: 

  • OSHA Hazard Communication Standards 
  • EPA environmental regulations 
  • Local fire codes and building regulations 
  • International shipping and transport regulations 

  

Conclusion 

While glycols are not highly flammable at room temperature, they are combustible and can pose significant fire hazards under certain conditions. The key to safe glycol handling lies in understanding its specific flammability characteristics, implementing proper safety measures, and using appropriate fire suppression techniques. Different types of glycols have varying degrees of flammability, with some requiring higher temperatures to ignite than others. 

The most critical safety consideration is ensuring proper concentration limits in fire protection systems, adequate ventilation in storage areas, and the use of appropriate personal protective equipment. With proper handling, storage, and fire prevention measures, the fire risks associated with glycols can be effectively managed while maintaining their beneficial industrial and commercial applications. 

Regular training, proper emergency response planning, and adherence to established safety guidelines are essential for anyone working with glycol-based products to minimize fire hazards and ensure workplace safety.