Determine the height of the "drop." For an actor to "disappear" on stage there must be between 4 and 6 inches of clearance from the trap door height to the "landing pad." For an actor to "appear" out of a trap door, the height factor differs. A floor-to-platform height of 48 inches can accommodate most adults if they will only be crawling out of the trap and then standing up. In order to make an actor rise out of a trap in a standing position, the platform must be the height of the actor in standing position plus an additional 12 to 18 inches for clearance. Magical "risings" out of trap doors require the use of some type of "elevator."
Provide the safest "drop" or "lift" distance for the trap door by elevating the stage using platforms. Cutting holes in the actual stage floor is normally prohibited. Trap doors can be built over an orchestra pit, however.
Determine the width of the trap hole. Measure any actors who will be using the trap. Add 24 inches of additional clearance to this width for safety. This measurement will determine the size of the platform unit containing the trap door system; make adjustments in stage designs accordingly.
Cut a square hole to proper size in the trap unit platform. Create a soft, deep "landing pad" under the hole. Test the "drop" using a "stand in" as the test subject; provide a football helmet for safety. Instruct the tester to drop into the hole, feet first, arms at their sides. Observe the results and make adjustments as needed. For "elevator" traps, test the elevator mechanism and adjust until safe.
Create a trap door. Cut a door from ¾-inch plywood, ¼-inch smaller than the trap door opening. Hinge this door to the underside of the platform, opening down. Test the fit of this door when closed, avoiding wide gaps. If the actor will be rising out of the trap on an elevator, make sure the trap doors can be fully swung down and out of the way and then secured in the open position.
Create a trap door locking mechanism. Install two or three 2x4s so they can be slid into a fixed track under the trap door to keep it closed and provide support for walking on the platform. Provide room to slide these 2x4 "lock bars" out of position when opening the trap. Test these mechanics thoroughly and make adjustments. Train technicians to operate this system flawlessly.