Abstract: A control for a treadle activated machine tool having a driving power and a mechanical treadle linkage connecting the treadle to the driving power. The control comprises at least one sensor for sensing the presence of an operator's hand remote from a work area of the machine tool and an interrupt for selectively interrupting the treadle linkage in response to a signal indicating the absence of the operator's hand from the sensor.

Abstract: A movable scaffold for use in gaining access to the inside wall of an upright cylindrical tank such as a petroleum refinery reactor tower. The scaffold comprises a central frame having four radially extending, adjustable arm sets each connected to a scaffold platform, or cage, and hydraulically actuated to bring the platforms into working proximity with the inside tank wall. The scaffold platforms are each connected by cables received over sheaves at the top of the tank to winches outside the tank. Said winches are controllable to rotate the platforms within the tank, and/or to adjust the elevation of the platforms within the tank.