Smoke flooded the A5 north of Milton Keynes earlier this afternoon after a warehouse accidentally activated a suppression system.
The suppression gas was from the warehouse and office units undergoing maintenance at Potters Lane, Kiln Farm.
Firefighters from Great Holm, Bletchley and Broughton attended and an officer attended.
The crews used four sets of breathing apparatus, PPV (positive pressure ventilation) fans and a thermal imaging camera.
Two men were given pre-cautionary checks by paramedics.