We consider models of reliability for systems with protection; these models feature various factors for increasing accident-free operation and efficiency. We determine limit values for the accident-free index that can be provided only by increasing the reliability of the protection system and the protected technological object. We show that high requirements for accident-free operation can be guaranteed if there is a control of the operability of the protection system and its recovery after a failure is detected. Experiments based on the method of Markov processes with rewards confirm our theoretical conclusions and allow us to determine the range of rational values of maintenance parameters.