B738 Engine QRH
Engine failure: leave ISLN valve in auto; turn off effected pack = ISLN valve open and live bleed pressurises both ducts. Effected eng bleed valve closed due lack of puff. Engine fire: Close ISLN valve. Live bleed pressurises only its own duct. Effected engine bleed valve closed; no puff + fire handled pulled. Why the difference with ISLN valve? For consistency why not close it for both cases. In the former, if inflt start required there can be a command in that QRH to reposition ISLN to auto or OPEN. I just have an idea that keeping things the same keeps them simpler, sometimes.