What happens when the duct suddenly squeaks and shakes in ship breaker?

From the text:

Nailer spread out his weight and lay still, heart pounding. Trying to sense the duct’s intentions. The metal went quiet. Nailer waited, listening. Finally, he eased forward, delicately shifting his weight. Metal shrieked. The duct dropped out from under him. Nailer scrabbled for handholds as his world gave way. His fingers seized scavenged wire. For a second it held, suspending him above an infinite pit. Then the wire tore loose. He plummeted. I don’t want to be a Jackson Boy I don’t want to be a Jackson Boy I don’t- He hit liquid, warm and viscous. Blackness swallowed him with barely a ripple.