The expansion-grate catwalk vibrated with his weight as he edged his way along the third tier to Number 92. The coffins were three meters long, the oval hatches a meter wide and just under a meter and a half tall. He fed his key into the slot and waited for verification from the house computer. Magnetic bolts thudded reassuringly and the hatch rose vertically with a creak of springs. Fluorescents flickered on as he crawled in, pulling the hatch shut behind him and slapping the panel that activated the manual latch.