PSV/PRV Discharge

Looking closely at the P&ID, there is also nitrogen coming in the header where the PSV is tapping from.

Normally you vent PSV/PRV discharges "away" from any contact with people when there could be a potential to do harm, and normally this is in the "up" direction. One issue here (and especially with your 142 ft of discharge length) pointing up it can act as a bucket and catch water (sometimes large qualities) so adds to the "harmful effect" during discharge, both to people in the area and to the piping system with severer water hammer! You can eliminate this by drilling a 1/4" Dia."bleed hole" just off the bottom weld on the elbow as the discharge piping goes up.
However "IF" it's just air (even with nitrogen) it's not harmful so I see no need to use 142 ft of pipe to discharge it vertically "IF" a shorter run horizontal is available? ...And as long as it’s not discharging where it would come in direct contact with people.
Also, if I under stand your description on the block valves, you have one valve on either side of the PSV/PRV? They BOTH better be Locked Open ...not just one valve!
Lastly your job as a "checker" is to verify that what is designed will work and there are no glaring faults, NOT to re-design it because you don't like it and/or you think you can do better.
(AND is why I hate checking!)

Thanks jop and 11echo! I'm still struggling to be a checker.