The key is to create your toxic plume slowly over decades instead of in a big showy bang
That single coal power station explosion I found on the first page of search killed more people than the Chernobyl explosion.
You joke, but the real key is to buy governments, advertising, and "activists".
Long term radiation from Chernobyl may kill anywhere from 100 to thousands of premature deaths, but I also don't count the continual nuclear and chemical disaster that is a normally operating coal power plant or its contribution to premature deaths, let alone its contribution to climate change. Only the deaths as a direct result of the explosion, just to go a little easier on coal.
If we want to compare the total scale of each disaster from start to finish, in terms of premature deaths then the coal disaster begins the day the boilers were fired up.
https://www.hsph.harvard.edu/c-change/news/fossil-fuel-air-p...