New York City requires FDNY certified individuals in several circumstances; some circumstances include:
Fire guards are required on construction, alteration and demolition sites when work is not in progress, except between the hours of 12 midnight and 8:00 AM.
(The number of fire guards required depends on the size and location of the field site. If the site fronts on one street, one fire guard is required for each 10,000 square feet or where the building exceeds 75 feet in height.)
NOTE: A summons will be issued if the required fire guards are not on duty during the required hours. The building owner will then have 72 hours to hire the necessary fire guards to patrol the premises.
 FIRE DEPT OF NEW YORK Consolidated Study Material
Who Needs Fire Guards?