Air isn't really a problem. A person breathes about .5 cubic meters of air per hour, so 100 people trapped for 6 hours will go through 300 cubic meters of air. The diameter of the tunnel being 14', that air supply would take up 68' of tunnel lengthwise. And that's one breath, the air can be breathed many times before the co2 level becomes too high.
The air inside the volume of a coffin can last you a few hours. Unless you are literally shoulder to shoulder with no other air, your oxygen will last as long as you need.
The air inside the volume of a coffin can last you a few hours. Unless you are literally shoulder to shoulder with no other air, your oxygen will last as long as you need.