I agree with the posts here, that the safety system should not be electronic. A physical switch is much better.
With that said, I'll answer DaveXRT's question about the snubber resistor:
And how big should be the 1k resistor be ?
For the snubber, it really doesn't need to be that big at all. A safe size would be 2W or 5W. The transient will be so short lived, that there will be no time for heating. The instantaneous power is immense, but it dissipates in nano-seconds. Lets do some math..
Depending on the actual inductance and resistance of the load, then the instantaneous power could be up into the terawatts, but the average power will be just a few kW, and that's only for 10ns or so. 2kW for 10ns will cause Q = 2000W*10ns = 20e-6 Joules of heat. The heat rise depends on the mass (m) and specific heat capacity (c) of the material that makes up the resistor. Some really good high-energy resistors have specific heat of 0.23 cals/gm K. The specific heat capacity of resistors varies from manufacturer to manufacturer, but let's assume two orders of magnitude worse than that really good one, and say we have a specific heat of .0024 cals/g K. That's 10 J/kg K. assume a 5W ceramic resistor has mass 4g (.004kg); hmm that's probably realistic, but lets make it lighter. Say 1g or .001kg
So the temperature rise is given by ?T = Q / mc
?T = Q / mc = 20e-6 J / (.001 kg * 10 J/kg K) = 0.002 °K temperature rise = 0.002 °C.
That's so small, it would not change in temperature at all. You could probably use a 1W resistor, or stay safe at 2W.