The heat of an arc is pretty much the same for all arcs, in the arc path. The amount of heat (Or Incident Energy) that radiates from the arc to a recieving surface a given distance away will depend on the available fault current and clearing time of the protective device as mentioned by BSH.
The heat produced from an arc can reach tempatures up to 36,000F, to put that into perspective, steel melts at about 1800F, the surface of the sun is estimated to be about 7,000F, so an arc can be 20 times the temp needed to melt steel or 5 times as hot as the sun.
Your boss dosent understand arc flash at all (Or he has asked you a trick question). The amp rating of a circuit has little to nothing to do with the arc flash hazard, a 1 A circuit being fed from the same transformer with the same clearing time would have almost the exact same hazard as the 200A circuit.
