This would have to be one of the best small scale demonstrations I have seen for demonstrating the danger of "cold grey smoke". My French colleagues built this small box and filled it with pyrolyis smoke from a boiling flask filled with wood chips. The bunsen burner heats up the wood in the flask (on the right side of the box) to the point at which it decomposes into volatiles which includes the unburnt fuel. Although the smoke is at a relatively low temperature, it can still be ignited if a flame is introduced!. One of my friends from Belgium gave me this clip and I am not sure of exactly where it came from. It you know the owner please let us know. They are to be saluted!
Shan Raffel