Which cooling class letter designation indicates a liquid with no measurable flash point?

The cooling class letter designation that indicates a liquid with no measurable flash point is associated with Class L. This classification is used for liquids that are typically non-combustible, meaning they do not ignite under standard conditions. Liquids in this category are often considered safe for various applications due to their inability to support combustion, making them suitable for environments where fire hazards need to be minimized.

In contrast, other classifications are designated for different characteristics. For instance, Class O includes liquids with a different range of properties that may allow for potential flammability. Thus, Class L specifically denotes the absence of a measurable flash point, indicating heightened safety in situations requiring temperature regulation or cooling in the presence of flammable materials.