So in the early days of Nuclear fission, there was a concern about the resulting energy igniting the atmosphere in a ball of fire and world-wide death which is awesome terrifying awesomely terrifying. This of course did not happen, and I'm led to believe that these concerns ran along the same vein as concerns raised about the LHC creating a black-hole that would consume the earth (read; sensationalist media fueled, the scientific community at large had no reason to believe this would actually happen).
To my understanding, fusion reactions generate orders of magnitude more energy than fission reactions. It's fairly obvious that hydrogen fusion is self-sustaining in the right environment (see exhibit A - The Sun), and elements up to iron release energy when fusing, so that includes most of our atmosphere. What reason is there to believe that successful achieving fusion in the confines of our atmosphere would not, y'know, set it on fire?
