I did a BoI many years ago when one ejectee landed in the fireball - survived but burns were exacerbated by failure to wear a layer under the flying suit, loss of a leather glove in the ejection and the fact that the LSJ burns rather easily, transmitting heat to the person beneath through the unburnt flying suit.
The Board's recommendation on the LSJ was rejected (cost?) - dunno if they have made it out of something non-flammable now?