Trips should not be disarmed without authorization

Many accidents have occurred because operators made trips inoperative (that is. disarmed, blocked, or deactivated). The following incidents are typical  

One day the inevitable happened. Having defeated the interlock, an operator opened a drain valve in error instead of a transfer valve. 

Protective equipment may have to be defeated from time to time, but this should only be done after authorization in writing by a responsible person. And the fact that the equipment is out of action should be clearly signaled—for example, by a light on the panel. 

Trips should normally be designed so that they operate if the power supply is lost. If this will cause a dangerous upset in plant operation, then an alarm should sound when power is lost. Trips should be tested at startup if they have been worked on during a shutdown. Particularly important trips, such as those on furnaces and compressors and high-oxygen concentration trips, should always be tested after a major shutdown. 

The most common cause of a high temperature (or pressure, flow, level, etc.) is a fault in the temperature measuring or control system. 

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