The first step to safe handling and use of heat transfer fluids is understanding fluid fire-safety ratings, including flashpoint, firepoint and autoignition, according to Duratherm Extended Life Fluids, a Lewiston, N.Y., manufacturer of heat transfer fluids.
Flashpoint is the temperature at which the vapors produced from a fluid will ignite (flash off) with the presence of an ignition source. While flashpoint is important, it is common for heat transfer systems to be operated at temperatures above the flashpoint of the heat transfer fluid.
Firepoint is the temperature at which the fluid will sustain a fire if ignited by an outside ignition source. It is not unusual for heat transfer systems to be operated at temperatures above a fluid’s firepoint as the fluid contained within the system is far removed from ignition sources.
Autoignition is the minimum temperature at which a substance must be heated to cause ignition without application of flame or spark. Never operate a system above a fluid’s autoignition temperature.
According to Duratherm, in a properly designed heat transfer system, fluids can be used right up to their maximum bulk fluid temperature rating, which is usually much higher than the fluid’s flash- and firepoints.
To understand how a fluid can be heated beyond a flash- or firepoint, the way in which the flash- and firepoints relate to a heat transfer system must be considered. In the case of flashpoint, vapors would need to collect or become trapped in a relatively confined space and have an ignition source to cause a flash. Regarding the firepoint, a properly designed system should not permit air/oxygen contact (which is needed for fire) at the heat source, such as a boiler or electric immersion heater. Also during normal operation, the fluid is contained within the system and away from external ignition sources.
In the real world, however, extenuating circumstances such as leaks can pose potential fire hazards. Leaks may result in fluid dripping onto a hot surface or an open ignition source, causing ignition. Remember that if any part of a heat transfer system starts to leak or smoke, it should be approached with caution and proper fire extinguishing media close at hand, particularly if insulation is smoldering.