- Save yourself with a flare.
- You bought yourself some breathing time/space with a flare.
While you are in the low-health state (under 25% health/grey state), simply pull out a flare. You do not need to be fighting for this achievement to unlock, you simply need to be in the low-health state. Simply let an enemy attack you for a while, then, when in the grey state light a flare. This can be done fairly early on in the game. However, count the moment carefully or you will die by the incoming enemy.