when is a CO2 extinguisher not suitable for a electrical fire?

Answer 1

I think I would be concerned about the use of CO2 to fight an electrical fire if any of the following conditions existed:

1. You had to fight the fire in a confined space and build-up of discharging CO2 gas could pose an asphyxiation risk.

2. If a large amount of other burning materials were present that CO2 is not rated to extinguish. Like Class "A" or "D" fires. (Fires involving flammable metals or large amounts of wood, paper, or trash.)

3. If the fire was too large to fight with a portable unit. Fire extinguihsers are designed to extinguish small fires, if the fire is too large, or you cannot fight the fire with your back to your exit, then do not take the chance.

That's my take.

Answer 2

The only reason not to use CO2 I can think of is when there are burning metals, like magnesium involved. Magnesium (and other high temperature) fires create carbon monoxyde when one uses CO2.