When looking at a mission, the hazard level is the yellow "warning" icon with the exclamation point in the center (not to be confused with the footprint shaped "Length" indicator or the lightning bolt sign "Complexity" indicator). You can start you own Hazard Level 3 game or join in on another player's game, either will earn you the achievement.
You don't have to be alive personally at the end of the mission to get this achievement, but at least one of your teammates must make it into the Escape Pod for the level to count.