Make sure you do this at the start of the game as the Fire Proof upgrade will make this impossible
Now, once you are within Hell head to anywhere in the city where there should be water, as in around the islands and you will find lava instead of water. Simply jump into the lava and Johnny/Kinzie will begin to walk on the lava and their health is rapidly depleted, after about 15 seconds they will die (Assuming you have full health) and you'll fall into the lava and die and the achievement will be yours.
You will also unlock
Heres a video.