Look at Captain Keyes’ abandoned pipe
Halo Combat Evolved NO SMOKING – Achievement Guide
Complete Skull and Terminal CHECKLIST(Halo 1-4 / Google Docs)
Once you find Keyes in the mission you will trigger a cut scene. After it’s over, step down the ramp a little bit and look to right of the platform. You will see a small pipe hanging down. If you look at it for a few seconds the achievement will pop.