Critical instrument systems proof testing

The integrity of safety instrumented systems is usually dependent on proof testing at specified intervals (often at a frequency between monthly and three-monthly). Safety management systemst2jsafety critical operating procedures such as described in (c) above are adhered to. 

Class 1 safety instrumentation loops include alarms and trips on storage tanks containing flammable or toxic liquids, devices to control high temperature and high pressure on exothermic-reaction vessels, and control mechanisms for low-flow, high-temperature fluids on fired heaters. Other Class 1 instruments include alarms that warn of flame failure on fired heaters, and vapor detectors for emergency valve isolation and sprinkler-system activation. All of these alarms, shutdown valves, and other critical instruments are regularly proof-tested to a well-defined schedule. 

The safety instrumented systems (SIS) and critical alarms assigned a Class 1 include those that have been mandated as such by state or federal agencies an in-house technical safety review committee HAZOP studies and specific alarms deemed critical by operations supervisors. All of these SIS and alarms are on a regular proof testing schedule. 

---