Fire Safety Concerns

Recently, I spoke to an owner of a data center who had been told that they should use a dielectric coolant with a very high fire point of 300 C. When pressed, this specification was given to him by a manufacturer of two-phase dielectric fluids with the explanation that this was the minimum fire point requirement for dielectric fluids used indoors.

The origin of this 300 C. fire point requirement is from the section of the U.S. National Electrical Code which is concerned with the fire safety of high voltage transformers that are installed indoors. I was on the committee that wrote the original section 450-23, back in the late 1970 and early 1980s.

In 1979, after a great deal of experimentation and input from many parties, the National Fire Protection Association determined that 35,000 volts is the required for a short circuit to input enough energy into a tank of dielectric fluid to raise the temperature of that tank to the fire point of the fluid. If a transformer of >35,000 volts is installed indoors, the US National Electrical Code requires that the dielectric fluid have a fire point greater than or equal to 300 C. Transformers of less than 35,000 volts potential do not have this requirement, and may use standard transformer dielectric fluid, with a fire point of 140 C.

Obviously, these high voltages and current do not exist in telecommunications or data center equipment. Even line voltage of 220V and 10 amps would never arc between two components or circuits because the dielectric strength of ElectroCool coolants is far above that. And if an arc were to occur, there is no chance that there would be sufficient energy applied to the coolant to raise its temperature above the fire point - fuses would detect the high current situation and close the arc far before the fluid got hot.

A 300 C fire point is not appropriate for low-power equipment where sufficient energy to ignite the dielectric coolant doesn't exist.

I hope that this helps explain some of the background of the 300 C. fire point requirement (even that number was chosen by consensus of a committee, not because it represents any threshold of fire safety). Cooling electronic equipment is not the same as cooling power transformers, and the safety requirements of each should reflect that.

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