Untouchables

Untouchables is an achievement for Left 4 Dead.

Summary
No Survivor takes any damage after contacting the rescue vehicle.


 * If a survivor is pinned by a Hunter or grabbed by a Smoker, if they are saved quickly, they will not receive any damage, and the achievement can still be obtained.


 * If a survivor takes falling damage, friendly fire, or fire damage, the achievement cannot be gotten.

Tips
Using the glitch ledge on the Rooftop Finale in the No Mercy campaign is a far easier way to get the achievement rather than using just skill and plain luck.

Quite a hard achievement, If you want to go for it just put it on easy and find a good spot and you should be able to do it

There are multiple ways to get this achievment, you can use the Developer console and change the infected spawn rate to 0 or play a campaign on Easy singleplayer.