Plants designed to earlier standards

Computer systems are different from conventional components with regard to MS I. Special tests and procedures are required to prevent, or to detect, defects or deterioration in computer systems. Computer based systems are more vulnerable to electromagnetic disturbances than are conventional systems. Static discharges caused by the accumulation of electrical charges from human body surfaces or from components may cause damage to devices or components which are used to store 

Computer based systems are used both to perform functions important to safety and to monitor and test systems important to safety. It should be ensured that computer based systems of both types are qualified for use and are maintained in accordance with their importance to safety. Maintenance activities on computer based systems should be carried out and managed in accordance with a maintenance plan that has been agreed between the user and the system developer prior to acceptance of the system. 

A programme for the periodic testing of computer based systems important to safety should include applicable functional tests, instrument checks, verification of proper calibration and response time tests. The periodic functional tests should include, but should not be limited to, the following  

For modified or new computer based systems, a probationary period of operation should be established during which in-service testing is undertaken more frequently. 

Further guidance on MS I for computer based systems important to safety is provided in Ref. [9]. 

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