While explosions aren't fun, if using AToW, internal explosions cause fatigue damage first, so 3x explosion hits wouldn't necessarily kill a MechWarrior:
AToW p217: "MechWarrior Damage Table:"
Event: MechWarrior / Internal Ammunition Explosion
Damage (AP/BD): 0E/4D (damage unaffected by armor)
AToW p179: Standard Damage vs Fatigue
If a character suffers more Fatigue damage than he has Fatigue bubbles to record it, the character automatically falls unconscious and any excess Fatigue points transfer to Standard damage.
If a MechWarrior were to have 4BOD and 4WIL, then they could survive three internal explosions' worth of feed-back, whereas the 4th would kill them. Increasing BOD or WIL to 5, makes 4 BOOOMS! survivable... but they may wish they had been killed.
Now the actual damage from the explosion on the other hand...
** Additional note - ammunition explosions wouldn't cause KO rolls per TW "pilot hits", but instead would be checked against the "Consciousness Check"
(AToW p180: "Any time a character sustains Standard damage from an attack, he also suffers 1 point of Fatigue. Attacks that already deliver Fatigue points (such as Subduing damage) do not add this Fatigue point).
(AToW pg184) at a TN of 7 +WIL Link Attribute mods +Injury +Fatigue modifier penalties