"Incinerated" may be a slightly strong word, but "fatally injured by burns" is entirely accurate. Most of the fatal and life-altering burns suffered in Hiroshima and Nagasaki were effectively extreme sunburn. Most of the burns victims were burnt only on one side of their body - the side facing towards the blast. It doesn't take a lot of material to protect you from that flash. Many people suffered burns only to their face and hands, while the parts of their body covered by clothing was uninjured. Some people had the pattern of their clothing burned into their skin; the darker colors of the pattern acted as a photomask. Eye injuries were very common, because many people heard the bombers flying overhead and went out to look.