I ran through a very bazaar situation in a discussion with one of my colleagues. We have an on-off valve on a compressor purge line. This on-off valve isn't ESD valve its connected to DCS and used during normal operation. Compressor supplier advised to close this valve on ESD trip signal. The question is: Can I use serial communication between DCS and ESD to take this action or should i use hard wired communication? This loop has no SIL and isn't essential for compressor shutdown.