How were the Manhattan Project scientists able to predict the possibility of the atmosphere igniting after using an atomic bomb, and how did they come to the conclusion that the atmosphere wouldn’t ignite?

Question

Did the non-zero risk of the atmosphere igniting increase as nuclear weapon yields got larger and larger?

Obviously a result of watching Oppenheimer.

In: 789

Answer 1

Let’s say you have a bag of wet sawdust. If it’s only a little wet, you could start burning a small bit of it, which would dry out the next bit of sawdust and allow the whole bag to burn. If it’s really wet, it doesn’t have enough heat to remove water and burn the next bit of sawdust. The atmosphere is basically “too wet” even though there is a lot of potential nuclear binding energy available.

Nuclear reactions sustain themselves if there is enough temperature and density. They looked at the energy made per reaction and figured out the energy lost given the conditions of the atmosphere and determined the nitrogen wouldn’t ignite. The suitability of the atmosphere to a sustained chain reaction producing more fusion energy per volume than dissipated is not changed by just having a bigger/hotter starting point.

Even if you burn some of the sawdust by adding more heat, it won’t spontaneously burn the rest of the sawdust.