Thanks Martin! Based on what I’ve read and understand, it can’t discharge into “trapped” drainage. Just to CYA, I’ll continue to point out and let the plumbers figure it out. 
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Of course it can. The TPRV discharge pipe, before the air-gap, cannot be trapped, but the drain (or a waste receptor) the discharge pipe discharges into can be, not a problem. The issue with trapping the discharge pipe itself is if it gets clogged now you have a potential ticking bomb.
I understand what you are saying and I agree. The terminology used in defining the situation is confusing to say the least. The blow off leg being trapped as opposed to whatever drain it may flow into? Going back to the OP’s pictures, no that is not correct by any means. And if I ever see a trapped drain for for a blow off, I’ll still call out.
Not sure that you do. You haven’t made your case other than claiming you’re confused by some terminology. There is no confusion, a waste receptor (with a ptrap) is an acceptable discharge for a WH TPRV.
Thanks for running with this one Simon. Maybe a different perspective will help clarify confusion. This subject is mentioned here often.
I appreciate your reply and will note that from now on…with a disclaimer…
Thanks for the insight!
Is Simon making trouble over here? 
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