On another good run; now a level 8 Marine with two exotic armors. I ran from The Wall, I am pretty sure with only one enemy left, because I had only 8% health, and no health items or skulls. I end up in a demon/cacodemon cave, and from health pickups end up with 15% health. Then I realise that the stairs are separated from me by one tile of lava, again. I have some Plasteel boots, which reduce the lava damage to 3/4 of it's normal value, but that would still do 15% damage and kill me. Fairly frustrated, I go looking through the cave for any health pickup I may have missed, when...
Argh!!! Lava! You die!... Press <Enter>...
I look at the screen, and eventually realise I stepped in a random lava square, which I had not noticed because it looked like the bloody and already red floor.
Seems like I need to pay more attention even once the level is clear; now my top two highscoring runs died to stupid missteps.
While running you take half damage from lava, which even ignoring your boots would have been enough for you to survive (with 3% hp left, which would have been either 1 or 2 health).
With your boots you would have taken significantly less, due to both the 2 protection and the 25% resistance, which would probably have reduced the damage taken down to 3.
After a bit of thought, the only way to have 15% health would be to be a marine (or have at least 1 level of the ironman trait) resulting in you having 60 max health, meaning you had 9. Running though would have cut you down to 10 health, and not running though set your health to exactly 0.
I could be wrong on the exact math, but I am pretty sure if you ran through it with the boots you would have survived. Your health would have been pretty low, and you might have died with a singlt hit next level, but you would have made it.
EDIT: I will note that if you start running while *on* lava/acid, you take a turn of damage while toggling it, so it isn't always the best idea to turn it on if you are just going to be on the lava/acid for a 1/2 turns.
EDIT2: Derp, you said you were a marine in the opening of your post, oh well, figured it out fine in the end anyways.
EDIT3: You could have saved your previous char by running as well. Oh well, tat least you know now.