CFD for Gas Detection Study

<Sigh>

The first step, surely, is to have <...CODE such as API RP 505...> to hand. Please respond after that has happened.

Depending on the classification of the gas, I believe it is assigned a minimum area for safety, as for placement of gas detection sensors, that is usually determined by cost analysis...

https://www.researchgate.net/publication/321762153_A_risk-based_methodology_for_the_optimal_placement_of_hazardous_gas_detectors

I'm certain this will change greatly on this unstated location. Similarly, CR4 should not be considered your Authority Having Jurisdiction (AHJ) regardless of where you or this installation resides. You will save yourself many steps by contacting them and asking them about this code. Now if the AHJ reply baffles you, then you can bring us both their reply and the relevant code (in verbatim) and we will gladly assist you to comprehending what is meant.

Some gasses are heavier than air, some lighter. This plays a large part in where the detectors are located.

Air movement is also a big factor.

Go find a gas detector manufacturers rep or a contractor who deals in these systems. They will help you lay it our for free.

I supply these system all over the world and I have never seen an AHJ who knew anything at all about gas detection. The Insurance guys sometimes know a little, but they will only get involved a small fraction of the time due to the liability of even small design changes.