PLC and Functional Safety Certification

DirectorDave,
Your question is a bit vague on what it is you're really trying to accomplish and you might need to define it a bit more.

IEC 61508 is titled "Functional safety of electrical/electronic/programmable electronic safety-related systems" and is intended to be a basic functional safety standard applicable to all kinds of industry. This standard may or may not be key to what you're after.

Keep in mind that now we have PLCs and Safety PLCs in industry. Some of those standards also may be helpful. I had an Allen Bradley paper here that a sales guy dropped off and I found it online. http://discover.rockwellautomation.com/Files/PLC-vs-Safety-PLC-Fundamental-and-Significant-Differences.pdf This paper also lists several standards that might help.

Another site that you might find helpful is http://www.plctalk.net/qanda/
I would think that if you better define your needs, someone there will certainly have an answer.

Good Luck