Several contributors have mentioned opening the DV window. Well, as we all know the 747 doesn't have one. But other types do. Many years ago I was involved in some tests, the first on a VC10, the second on a 707.
On the VC10 we lit a smoke generator in the middle of the flight deck and opened the copilot's DV window at around 5000ft and 210 kts. The result was so much noise we could only communicate by hand signals and the smoke streamed forward and then past the copilot's instrument panel further reducing visibility. I think we also tried speeds up 250kts with the result that noise level only got worse. When we tried the captain's DV window the result was the similar on his side.
Some years later I tried the same on a 707 but without a smoke generator, so were unable to check the effect on the visibility. But the noise levels were very high making cockpit communications almost impossible.
Clearly in extremis it might be worth trying to open the DV window, but I would be very, very wary of doing so in view of the above results.
Several people have mentioned how hazardous fire in the air is. I agree. Unfortunately check lists can be of doubtful value. There is really only one option and that is to get on the ground ASAP.