NFPA 86 - delay of pressure proving on gas train

[jtb2]

I am looking at section 8.2.8.2, which seems to allow delay of gas pressure interlock of gas train block valves.

I have two questions.

1. Does condition (4) mean that only one of the low pressure or high pressure switches may be delayed, or may they both be delayed?

2. Can this delay be implemented from a PLC timer that is not SIL2 rated?

3. What specific delay equipment would typically be approved for this use?

Thanks.

 

[jtb2]

Yes, I had three questions, not two.