Kill switches are not a very good idea unless they are designed to shed electrical loads gradually which is quite possible in the same way airliners have different busses. A straight forward off switch is liable to do more damage than the reasons for using it - if there is a small fire why kill the smoke extraction system, if there's a big fire its too late to turn off the power anyway.
If someone feels the necessity for such a devise it has to be behind a guard to prevent accidental use or behind glass in a break glass emergency case and in any event it is questionable as to why one person is allowed to work alone on something of this scale in todays world especially if they are a contractor -oh there is one reason, its cheaper, wonder which policy BA adopted.