My thoughts from all the way back in 2017 (!) about World War Z and the proper way to clear out zombies.
As I have mentioned before, I think the Paris authorities in World War Z took entirely the wrong approach to cleaning out the catacombs under Paris. They sent people in to, essentially, go hand-to-hand with zombies.
If it had been up to me, I would have gone around and put up zombie-proof barricades at every exit to the catacombs. Then I would have gone to each exit in turn, set up a zombie-proof corral with gunmen in safe positions, then removed the barricade at that exit and turned on the loudspeakers. Every zombie within earshot comes a-running (presumably there aren’t any on the loose by this point, but I’d post guards looking out, just in case). The zombies from the catacombs rush out into a killing field and nobody gets hurt stumbling around in the dark.
I wonder if zombies are dumb enough to run into flames. They are depicted as dumb enough to run off of cliffs and buildings in an attempt to reach people on the other side of a canyon or street, so quite possibly they are. If so, I’d pour gasoline into my killing field, and once we had a good crowd of zombies, fire a Roman candle or the like into it. The zombies already there would be destroyed and any more that ran out of the catacombs would be likewise. This assumes that there’s nothing flammable in the area, which I think would likely be the case – wouldn’t the catacombs open onto streets or even drainage culverts? At least, that’s what I’d try anywhere it was practical.
At any rate, I’d lure zombies out of each exit in turn, making the circuit several times until there were no more zombies coming out of any exit. At that point, we can be pretty sure there are no mobile zombies within earshot of the exits. So then I’d send people in with really good lights, zombie-proof gear, breathing equipment (from the description in World War Z, the atmosphere in there tends to be pretty foul), good weapons with lots of ammo, and portable barricades. They move in slowly, checking for non-mobile zombies, and blocking up tunnels and passages as they go so that they can methodically check the whole place. It might take months. What’s the hurry, as long as the exits are kept blocked?
The same approach works for any building. Block all exits but one and lure any mobile zombies to that one. If you have doubts (maybe there are no zombies and the building contains survivors), then be ready to move any fleeing humans into quarantine until you can determine their status. Once you’ve ensured there are no mobile zombies, you can move in with your portable barricades, going room by room, floor by floor, dealing with any remaining zombies and rescuing any humans sheltering in safe spaces.