These zombies will be asleep if you still have the Lighter, and will come to life after you have used this along with the Detonator on the locker. If you do not have the Lighter then these zombies will be up and waiting for you.
Available here when you are playing as Chris. It is on top of the box next to the conveyor belt. You need to refill the Empty Extinguisher inside the Water Tank Room, and then you can put out the fire in this room to access it the weapon.