Testing should be thorough

All protective equipment should be tested regularly, or it may not work when required. While it is sufficient to test relief valves every year or every two years, instrumented alarms and trips are less reliable and should be inspected every month or so. 

Testing must be thorough and as near as possible to real-life situations, as shown by the following incidents  

Emergency valves should be tested against the maximum pressure or flow they may experience and, whenever possible, should be installed so that the flow assists elosing. 

Another example a mixture of a solid and water had to be heated to 300°C at a gauge pressure of 1,000 psig (70 bar) before the 

Usually closes when trip operates but had failed in open position. 

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