You smoke 10 joints (equivalent tar to 20 cigarettes) per day, each leaving 20mg of tar on your lungs. That's 200mg per day, but your lungs can only remove 60mg per day, so 140mg per day accumulates.
0.14g x 365 days x 10 years = 511grams or half a kilo of tar accumulated every 10 years. Tar is twice the weight of water, so half a kilo of tar is one quarter of a litre and the average lung capacity is about 2 litres, the average breath is only 0.5 litres so you can smoke 10 joints per day for 70 years and still breath, just.
If you're insane. If not, do ashtanga yoga, protect your lungs.
The maths tell you, that people who smoke 40 cigarettes per day are going to run out of lung space within 40 years. When 80% of schizophrenics smoke this much or more, is it any wonder they die early, and isn't it a great chance to prove that people with schizophrenia are remarkably cancer-resistant (true!!!)?