Need Help with New Security Standards

We are creating a new Control Room. I'm told that we need physical security to conform to NIST TIER 4. All the information that I can find about Tier 4 only deals with Cyber-Security and not Physical Security. What standards are there that deal with SCADA Control Room Physical Security?

Physical security covers quite a range of factors, ranging from fire protection, achitectual design, electrical backup, manned security access, etc., etc.

The physical security minimums are largely governed by your customers requirements, the "cost" of loss, etc., etc.