This glitch is on the 2nd floor on the Five map. First thing you need is to get down there as early as you can. 5 - 7 is the rounds I would normaly do it at.

You need to keep 1 zombie alive make it a crawler (if you can turn the power on and get jug that will help you).

Now what you need to do is go to a little fence next to the orange floor (not where the random box can be, the other one) and you will need to stand at the end of the fence.

Wait until he is about to hit you then you jump just as he hits you. If you get on the fence walk to the machines and jump.

You now should be on top of the machines and they can not hit you.

If you play with friends that do not get up you can revive them if they can make it to the stairs.