I have found some info concerning these two topics on this live journal but I also found some info while searching on yahoo and google but nearly all the info that I've found contradicts each other.
1) Could a coffin be completely buried without buckling or collapsing? If it were buried less than six feet deep? If the dirt were shoveled on by hand and therefore more slowly than on mythbusters?
2) How much would/could the depth that the coffin was buried affect the length on time it took the person inside to suffocate? Would my character survive longer if he were buried under less dirt?
Lets say my guy is successfully buried and the coffin is holding up underneath the weight of the dirt.
3) Taking into consideration that my guy is not completely without oxygen but just receiving a very low amount of oxygen, about how long would he be awake and:
coherent? 1-2 mins or less? more?
delirious? 1-2 mins or less? more?
4) Overall about how long would it take for him to die?
5) Would he have time to think? Be frightened? Sad? Remember things?