What are the chances of a male under 20 who smokes pot daily lungs collapsing? how much does pot increase the chance of this happening?

Some increase: One risk factor for developing a pneumothorax is smoking from a water pipe (bong), as the deep inhalations and long breath holding put the lungs under pressure. It is not clear if the pot itself is a risk or the use of a water pipe alone is the problem, and it is not known how often this happens as a percentage of all use.

Higher: Population age adjusted rate for primary spontaneous pneumothorax (psp) is 7-18/100, 000. Estimated 80-90% of psp cases occur in smokers or former smokers. Males that smoke have 7-100+ times higher rate depending on how much they smoke. The risk factors for psp and secondary sp includes smoking (both tobacco & marijuana).