A320 :APU start during refuelling
 

In my airline APU start during refueling is not allowed . The reason : a very vague explanation is given in OMB , regarding the fuel track being too close to the APU , alluding to possible fuel vapor from the track being ignited during APU start .
AIRBUS itself does not have such restriction . The only concern for Airbus on this matter , is a potential electrical transient of the APU gen (APU gen taking over from the external power ) which could stop the automatic refuel process .
I'd like to know how other operators handle such issue and what restrictions if any you may have .
Thank you

It's correct. I don't know the distance, but A320 is less than the required distance, A330 is large enough.

It's the distance between the APU exhaust and the aircraft fuel tank vents that is critical.
On the A330 there is a vent in the horizontal stabilizer that is considered to be within the critical zone.
Anyway, it's good practice to not change power sources during refuelling. Glitches do happen.

Is this critical zone published somewhere ?