Lockouts, Lockins, and Interlocks

Isolation, lockouts, lockins, and interlocks are some of the most commonly used safety measures in the process industry. These controls are constructed on three basic principles, or else on combinations of the first two. The three principles are  

Preventing incompatible events from (a) occurring, (b) from occurring at the wrong time, or (c) from occurring in the wrong sequence. 

Providing a release after suitable and correct action has been taken. 

Isolation employs separation as an accident prevention measure. Incompatible conditions or materials that would create a hazard if brought together are kept separated. Examples 

Interlocks are commonly used safety devices. The function of an interlock is to prevent the occurrence of an event in the piesraice of certain conditions. Some interlocks prevent action or motion, others send signals to other devices that prevent the action or motion. They automatically reconfigure or interrupt final control devices if monitored variables deviate significantly from specifications. Typical process variables monitored are flow, pressure, level, and temperature. Typical machine variables monitored are coolant level and temperature, lubricant level and temperature, vibration, speed, etc. Interlocks allow equipment to start and operate only when monitored variables are within designed specifications. Interlocks inhibit unanticipated actuation of equipment and ensure correct startup/shutdown sequences are followed. A permissive interlock will not allow a process or equipment to startup unless certain conditions are met. There ate two types of interlocks—safety and process interlocks. Each serves a different function. 

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