While Quatermass (John Robinson) is slinking around the plant the regular workers are breaking through the gates. The workers take over a strategic area in the plant. This is where all the gases are sent to the domes. Quatermass joins them and tells them that inside the domes the ammonids, as Quatermass calls them, are growing. To stop them they need to disrupt the process. Since oxygen is deadly to the aliens, the workers decide to stop the ammonia gas and pump in oxygen instead. The oxygen is beginning to work.
The infected humans, whom the regular workers call zombies, attempt to talk the workers out of their plot. One of the men, the shop steward, E.G. McLeod (John Rae) begins to yield to the propaganda being sent over the loudspeaker system in the plant. He and two other men agree to come out provided they are given the opportunity to see inside the dome. Quatermass and the head of the rioters, Paddy (Michael Golden) try to talk them out of it. The infected guards use the men to block the oxygen intake pipe. Furious that his friends have been killed in such a horrible way, Paddy fires on the dome destroying it and releasing the poison gases.
Using an oxygen mask, Quatermass manages to escape and is found by Dr. Puch (Hugh Griffity). The two men return to the Rocket Group. Quatermass decides they must use the rocket to destroy the asteroid. However, there is a major snag in their plan.
Thirty workers from the Shell refinery were used as extras in the food plant riot scenes.