Heat transfer fluids are considered highly safe when they are properly chosen for the intended application and basic usage and handling practices are followed.

To begin with, it’s crucial to be familiar with your fluid’s safety ratings regarding fire. These include the flash point, fire point, and auto-ignition point of the fluid.

Flash Point: This is the temperature at which vapours from a fluid can ignite when an ignition source is present, though the fluid itself won’t burn at this stage. Many applications, as well as updated fire safety regulations, may require fluids with higher flash points; however, it remains common practice to operate heat transfer systems above the fluid’s flash point temperature.

Fire Point: This is the temperature at which a fluid will continue to burn once ignited by an external source. In most heat transfer systems, the fluid often operates above its fire point because it remains safely contained and separated from ignition sources.

Auto ignition: refers to the lowest temperature at which a fluid can ignite on its own, without any external spark or flame. Systems should never operate at temperatures above a fluid’s autoignition point.

To sum up, heat transfer fluids are meant to be used at temperatures above their flash and fire points, but never above their autoignition temperature. How do these definitions fit into heat transfer operations? In a well-designed system, fluids can be safely heated up to their maximum recommended bulk temperature, which typically exceeds their flash and fire points.

Understanding why heating beyond the flash or fire point is safe requires considering the specific circumstances inside a heat transfer system. With flash point, for ignition to occur, vapor would have to gather in an enclosed area and come into contact with a spark or flame. In a well-built and reasonably safe system, this situation is highly unlikely.

When it comes to the fire point, proper design ensures that air or oxygen does not come into contact with the heated fluid at critical locations like boilers or electric heaters. During standard operation, the fluid remains sealed within the system and far from any external ignition sources.

Special Considerations – leaks

In practical terms, though, certain situations—such as leaks—can create serious fire risks that must not be overlooked. If a leak occurs, it may lead to several dangerous outcomes, including the following:

1. The liquid comes into contact with a heated surface or exposed ignition source, such as an electric pump, where there is a risk it could catch fire.
2. If a fluid leak occurs and the liquid gathers within the insulation surrounding system pipes or reactor jackets, safety risks escalate—especially when open-cell insulation is in use. For this reason, closed-cell insulation is strongly advised. When fluid seeps into open-cell insulation, it can begin to oxidize, generating heat that becomes trapped between the process piping or reactor jacket and the insulation itself. As the fluid continues to break down, its fire safety thresholds drop, and combined with the heat from degradation, the trapped fluid may start to smolder. This could result in an auto ignition-type fire should air be introduced to the mix.*

*It’s crucial to remember that if a section of your heat transfer system begins to leak or emit smoke, you should exercise caution and ensure that appropriate fire extinguishing materials are readily available—especially if you notice insulation smoldering. Often, the immediate reaction is to remove the smoking insulation to check what’s happening underneath. However, doing so can expose the area to air, providing the oxygen needed to trigger an autoignition fire.