The hazard
Confined spaces can look harmless from the outside. The air inside can be short on oxygen or hold toxic or flammable gas you may not see or smell, and loose material like sand or grain can bury a worker. When someone goes down, the natural reaction is to rush in and help, and that can turn one victim into two.
The action
The attendant is posted outside the space and keeps an accurate count of who is inside. They stay in contact with the entrants, order everyone out when conditions turn dangerous, and call rescue as soon as entrants may need help. They stay outside until relieved by another attendant. (29 CFR 1926.1209)
ASK THE CREW
Which spaces on this job could be confined spaces, and which ones are marked as permit spaces?
From the talk: Confined spaces. Read it in full, free, with the questions and the sign-in sheet.