Safety requirements specifications (SRS) are specifications that describe every required safety function that must be performed by a safety instrumented system (SIS).
SRSs specify both what safety functions must be performed by a system and how well those functions must be performed.
An SRS is designed for two primary purposes. First, it guides the design and creation of a safety system depending on the requirements of the workplace using the system; second, it provides the employees in that workplace with a clear explanation of the safety capabilities with which they are working. A clear understanding of the specific functionality of a safety system is important to mitigate workplace risk. A poor understanding of safety capabilities is a major cause of accidents involving control systems.