Alex had gone inside the power plant to set off the bombs himself because the detonator was broken, and he didn't make it out fully intact.

You had gone to find Alex when the explosion went off, causing you to fall on your ass.

Alex was slumped against a wall, regaining consciousness as he looked down and realised that half his left leg was missing. You rushed over to see if he was okay and saw what had happened. You panicked as you ripped off your sleeve and tied it around Alex's leg tightly.