At times as many as 40 firefighters and other rescue workers climbed on the debris pile, looking for even a hint of human remains.

These debris piles were then altered by steam and hot water flowing through them.

Firefighters and others who work atop the debris pile are supposed to wear respirators at all times, but not everyone does.

The debris piles were getting higher and higher.

They are most frequently found under leaf litter or debris piles, and are sometimes turned up during gardening.

Strange hummocks are found in this area which were debris piles created during coal mining operations more than a century ago.

But even then, the air above the debris pile was known to be more dangerous than the air in the rest of Lower Manhattan.

The opening is artificial, and has a permanently placed ladder descending to a debris pile.

The food service site on Cedar Street abuts the debris pile.

During the summer months snow-melt streams flow beneath the debris piles and cause caves to form in the ice.