Clarification: The lethal dose, not the LD50. LD50 means the lethal dose is 50… I forget what. Mathematically, you would have to smoke so much marijuana in an hour that you would not have enough rooms in your lungs for oxygen. You would die not because of the marijuana (smoke) but due to the lack of oxygen. Therefore, as long as you are getting enough oxygen, you cannot die from smoking too much marijuana. (If you had a different way to oxygenate your blood, maybe you could. But I think the lethal dose is strictly hypothetical and nobody has been able to reach it. Outside of laboratory conditions you wouldn’t be able to get close, anyway.)