Environmentally friendly non-flammable diluents are non-flammable mainly because their composition and physical and chemical properties determine their non-flammability. Here are some key factors:

1. Chemical composition:
   Non-flammable diluents are usually composed of chemicals that do not burn or have extremely high ignition points. These components include water, inorganic salts, non-volatile organic compounds, etc. For example, some non-flammable diluents may contain a large amount of water-based components or use organic solvents that are difficult to burn.
2. High flash point:
   Flash point refers to the lowest temperature at which the surface of a liquid produces enough flammable vapor and can be ignited. The flash point of non-flammable diluents is usually very high, even exceeding the temperature of normal temperature and general working environment, so that the risk of fire is completely avoided under normal storage and use.
3. Low volatility:
   The molecular structure of non-flammable diluents is designed to be non-volatile, thereby reducing the possibility of forming flammable vapor concentrations in the air. Even under high temperature conditions, these diluents are not easy to release volatile organic compounds (VOCs), thereby reducing the risk of explosion and combustion.
4. Slow oxidation reaction:
   Some non-flammable diluents are achieved by selecting substances with a slow oxidation reaction rate. Such substances are difficult to undergo rapid oxidation reactions even when exposed to high temperatures or open flames, thus preventing the occurrence of the combustion process.
5. Adding flame retardants:
   Some environmentally friendly non-flammable diluents may add special flame retardant ingredients that can improve the thermal stability of the diluent and form a protective barrier at high temperatures to inhibit the combustion process.