Brooklyn man arrested in fire that hurt 31

A 56-year-old Brooklyn man was arrested yesterday for setting fire to a Sunset Park apartment building, injuring 23 residents and eight firefighters, some of whom were caught in a stairwell collapse, officials said.

Fire marshals yesterday nabbed Chiu Tsang, who lives blocks from the Sunday blaze, after he was caught on surveillance tapes and made incriminating admissions to investigators. A motive for the arson, however, remains unclear, marshals said.