A safety control device for safely controlling a hazardous installation has a first and a second calculation unit and an output unit for driving at least one actuator. The control device acquires an input signal and determines a floating point value depending on the input signal. The first and second calculation units each determine an input interval as a function of the floating point value. The first and second calculation units each further determine a result interval as a function of the input interval by applying a first calculation algorithm to the input interval. The first calculation algorithm is based on interval arithmetic. The result intervals from the first and second calculation units are compared and an output value is determined as a function of the result intervals. An output signal is determined as a function of the output value. The output signal drives the at least one actuator.