This thread touches upon the most dangerous aspect of long range operations.Engine fires are relatively easily extinguished, cargo smoke/fire is contained by sophisticated suppression systems.The significant danger is fire or smoke in the cabin.No aircraft, flying short or long-haul, ETOPS or not, 2 or 16 engines, is immune from the dangers that cabin fire or smoke present. On a shorthaul network, the aircraft can be landed ( generally) within 30 minutes, though even this may not be sufficient time. On longhaul sectors this option is not available and the consequences could be catastrophic.
The Swissair incident demonstrated how lethal and incapacitating fire and smoke could be, if contained within the cabin, a survival time circa 20 minutes. In the 70's, there was a DC8 departure out of Jeddah which had a gear fire on takeoff ( due to a tyre failure) which was retracted into the fuselage.The surrounding structure then caught fire and even though the gear was extended again, the airblast from the slipsteam caused the aluminium structure to burn. The aircraft crashed about 2nm from touchdown only 5 minutes later, as the wing structure folded.
Experience shows that you have about 20 minutes survival if you can contain the fire/smoke within the cabin. If the fire gets through the structure and is fed by the outside airflow, you have only minutes. Even 16 engines will not save you.
My standard brief to my co-pilots,when we are in the middle of nowhere and I am off the flight deck, is: In the event of cabin fire/smoke 1.do the drill.2get descent to MSA 3.Call me. If the fire/smoke hazard clears, we can climb back up and look at the options. If it turns out to be uncontainable, at least we can force-land or ditch under control within 10 minutes, rather than crash and burn.