What is the gas composition in a tank with a SF6 leak?

[Graaf van Vlaanderen]

We discovered a leak in a SF6 gas HV circuit breaker. Since we don't know when the leak occurred due to temperature changes I assume there is only air left in the tank.
Here is my question. Suppose I have a tank with a fixed volume filled with air at the same pressure as the atmospheric pressure. When we add SF6 gas up to 0.2bar over pressure, what would then be the percentage of each gas (air and SF6) in the tank?

 

[Bystander]

You have three numbers; what do you calculate from them?

 

[Graaf van Vlaanderen]

Well, I consider T and V constant, hence n_tot = n(air) + n(SF₆) => p_tot = p(atm) + p(SF₆)
Hence %SF₆ = (0.2/1.2)*100. Not sure this is correct.

 

[Bystander]

You got it.

 

[Khashishi]

But I'd expect all the SF6 will pool on the bottom of the tank.