The logic of the software (SW) operation is critical for ensuring the safety of systems of critical infrastructure objects (CIO). When such systems are put into operation, it is the SW what renders majority of the decisions of control with minimization of data entry by operators. For a system that meets all security requirements, it is absolutely essential to ensure good quality SW. CIO designers adhere to industry regulations to create secure systems. This article proposes practice improvements in quality assurance that system designers can use in the SW development process, as well as an algorithm for evaluating software quality.