How come this Extremis Soldier died so easily?

Question

In Iron Man 3 Stark first meets this woman (Brandt) who was an Extremis soldier in a bar. He was able to kill her with an explosion.

However, in an earlier scene, another Extremis soldier (Savin) who was also caught up in another explosion, survived. Furthermore, he was also shot in the head by Stark after he killed that Brandt woman but he, again, survived.

Brandt's body was still intact after the explosion whereas Savin suffered more serious injuries (he has a hole in the head after being shot by Stark, for example). How come he survived while the other one didn't?

Answer 1

Brandt was from earlier trials of Extremis (she is seen on the videos regrowing an arm during an early set of the experiments).

Savin is from after the work has been more refined, similar to Killian himself, who shows a number of additional abilities on top of the regrowth/strength of the earlier instances.

Note that in the early part of the film, Tony is investigating the mysterious "explosions without a bomb" which are the result of early Extremis treated victims going critical.

The process itself is clearly not 100% effective or when Killian shoots Maya Hansen, he wouldn't then be offering Tony a "high level position" to perfect it - Tony even notes that he "almost had this 20 years ago, when I was drunk" so expects that he could figure it out fairly easily.