From the Hong 曾 Family's American Diaspora Files†:
On September 11, 2001, Zack ZENG Zhe 曾喆 was working at the Bank of New York at One Wall Street near the World Trade Center. When his building was evacuated, Zack could have gone home like the rest of his colleagues. Instead the 29-year-old gathered all the first aid and medical supplies he could find and told his friends and colleagues he was heading to the disaster scene to assist.
While attended the University of Rochester college Zack had worked as EMT with the Brighton Volunteer Ambulance. So, on 9/11, Zack was doing what he was trained to do.