Interesting little film. The bit with the magnesium flare reminded me of a photographic trip into High Gill Cave near Dent in the late 1950's to take a picture of the waterfall. I used some magnesium ribbons without realising the amount of smoke they created. I tried to beat the smoke to the entrance but failed and had to grope & cough. Had I waited 5 minutes it would all have gone out with the draught. You live & learn!Anyone who is familiar with Treak Cliff Cavern, or who knew Peter Harrison, may find this short film of interest: