If you examine the CVR transcripts, you'll notice that the pilots smelled "something" and that they eventually saw a little smoke. They elected to land, sending a PAN PAN PAN and began their smoke in the cockpit checklist. Decisions by the crew were accurate and correct for the circumstances, they WERE too heavy and so they simply HAD to dump fuel first. The situation was not so bad to risk an overweight landing that might result in a crash with casualties. As a pilot you are drilled not to take hastly and panic decisions, yes, you like to land as soon as possible, but only when you can do this safely, without the risk of a crash. Proof for the not so bad situation is the "pan" callout, only used for priority calls without any immediate danger for pax. and/or crew.
At the beginning of the dump, the situation suddnly became a lot worse, maybe, the melting (smoke) resulted then in an actual fire, and the crew became increasingly nervous due to the change. They announced an emergency and wanted to land immediately, stopping the dump. At this stage, all avionics blacked out, thick smoke filled the cockpit, and temperatures began the rise.
The crew stuggled to keep control, but temperatures went up and reached a level where the composite materials melted (around 300°). It is possible that at some stage the grew elected to ditch in the ocean, leaving the cockpit which was already on fire after putting the plane on a gentle glide towards the sea. Rumours are (I can not confirm this) that all passengers had to go to the rear of the plane, where the chances of survival are the best in case of a ditch.
The pilots, under command of Capt. Zimmermann did everything in their powers to prevent this tragedy, and I am appalled of some media, mostly in the US who critisise their actions. Simulator exersises show thet an overweight landing would have resulted in a crash at Halifax.
Let us never forget the tragedy that happened thtat day, I certainly will never, just for the fact that I was supposed to be on SR111, was it not for a spare seat on Sabena's flight from ORD a day earlier. Let us also not forget the role of the CABIN CREW, who are often forgotten but who had the impossible task to calm down passengers and keep cool in this hot situation.