You'll know you're in the right spot if you're in a room with a bunch of shelves and a dude laying on the floor behind a fence. You can't go through the nearby door, but you can crawl into the ventilation shaft and drop into the room through the ceiling. Do that, then grab the Maintenance Jack from his body and loot the surrounding area for supplies. When you're done, use your new toy to pop the door open and exit the room