Fix the mine's air purifier.
The broken air purifier
Talk to Zaius inside the house outside the Broken Hills mine's entrance. He will tell you the mine needs parts for the air purifier and asks you to go to New Reno to pick them up. You can either take the reward for money, or, you can decline, and receive a combat shotgun when you finish the quest.
Return to Zaius and he will ask you to enter the mine to fix the purifier. The mine is filled with radon gas, which will damage you and your party for about 5 points of damage every few steps. If you or any of your followers have power armor equipped, it will negate the damage. Use the parts on the clanking machine in the back (but watch out for the deathclaw!) for 1000 XP.
Return to Zaius and he will give you a City-Killer combat shotgun (or $500 if you asked for a reward earlier).
- It is advisable to do this quest before finding out who Killed Richard Wright in New Reno, since one of the possible outcomes of that quest is to have Renesco killed, thus rendering this quest unsolvable.
- Once the purifier has been fixed, the player and the party will no longer suffer damage every few seconds.