How do you design and implement safety interlocks and emergency stop circuits?

I suggest following steps while designing and implementing safety interlocks and emergency stop circuits which are crucial in ensuring the safety of personal, equipment and industrial processes. 1. Understand the Requirements ISO 13849, IEC 61508, ANSI/RIA R15.06. 2. Risk Assessment SIL or PL requirement? 3. Select Safety Components 4. System Architecture 5. Emergency Stop Circuits Dedicated emergency stop circuits. 6. Interlocking Systems Ensure that interlocks are tamper-resistant and fail to safe conditions. 7. Safety Logic Programming 8. Documentation and Labelling 9. Testing and Validation 10. Continuous Improvement (Cyclic PHAs, FMEAs) 11. Training and maintenance

Safety interlocks may be classified into two categories, however, that does not necessarily mean the two should be treated as mutually exclusive methods. PLCs, for example, can play an essential role in interlocking, monitoring, and providing varying degrees of backup to the hardwired circuits. For example, a hardwired safety contactor that removes power to a motor should also be monitored such that the PLC output to the motor contactor turns off as well.

Testing plays a large role in any safety system. In some cases, testing down to the component level after construction should be done. This includes, but is not limited to, an inspection of completed wiring, observing wiring practices, and even tracing individual circuits. Just observing the results of a safety functionality test may not be sufficient to adequately ensure designed architecture has been correctly implemented.

> Emergency stops should be provided in multiple areas of the processing plant like inside the operator's room, near the confined space areas, moving parts like conveyors, mixers, etc. > Each emergency push button unlock key should be kept by an authorized person so that nobody would be able to release the key except the authorized person once it is locked. > Install a safety pull cord on either side of the conveyor body. > Design the circuit with electrical and mechanical interlocks to prevent any unwanted activities. A mechanical interlock is assembled between two contactors to prevent them from working simultaneously. > Interlocking also can be achieved by PLC programming.

I think it's important to note that if the risk assessment warrants it, safety-rated functions on VFDs (STO or safe-torque-off) must be used with proper wiring or safety-rated fieldbus protocols.

What wasn't mentioned here was risk assessment, without that, you don't even start talking about safety. People, liabilities, errors and potential or threaten risks go before the selection of a single safety component. Walk down the facility, assess their he risk, build a report, then start working on picking the correct device. Another thing to consider, in an existing system, the relocation of LOTO mechanism and operator interface, and of course, the review of the existing safety system. On top of it, identify if any SIL level needs to be accomplished, for example on hood guarding to where two or more contacts has to come back within a certain time. Redesigning the circuits and introducing safety rated components is crucial as well.

Machinery Safety equipment, hard guarding & PPE play a vital role in keeping people/ equipment safe. It’s training, maintenance, & improvements that are the most important pieces of the safety lifecycle. Humans often take machinery for granted, & their dangers too lightly. If something was safe yesterday, it doesn’t mean it is today. Testing, following procedures, & continuous improvement is crucial. Safety systems can be designed well, validated, & appropriate procedures put in place, however, there is something about us humans that push the limits on nearly everything. We wouldn’t be where we are today without pushing boundaries, but we often forget that severe injury or death is one bad decision away. Better to be safe than sorry.