Abstract: A floor hatch with a built-in security fence is described, where access to the understructure can only be provided wherein a pair of doors are pivoted outwardly to an open position and secured, forming two opposite sides of the security fence; a first gate is pivoted outwardly to an open position and secured to each of the doors, forming the rear of the security fence and a second gate, leaving a pivoting door, is pivoted outwardly and secured to each of the doors forming the front of the security fence. The pivoting door of the second gate pivots outwardly to permit access to the opening in the floor. The floor hatch may also include a security grate and telescoping extension on each of the doors. The floor hatch can be locked in the closed position and can be opened, automatically forming a security fence, to permit access to an understructure of a floor.