I suppose doing it underwater would probably work, given that it isn't exposed to atmosphere. I'm not sure if smaller yields would help, since if larger yields

I suppose doing it underwater would probably work, given that it isn't exposed to atmosphere. I'm not sure if smaller yields would help, since if larger yields have a higher chance of setting the atmosphere on fire, we've set off some pretty big bombs and AFAIK the margin for devastation was already not huge for Trinity (not an expert though)