We leave a Class 1 Div 2 area at a pipeline tie in point and go into the ground. Our equipment is on this side and consist of pressure transmitters, valve actuators, and gas detectors. All of this equipment has EYS's installed. Where we go into the ground on this side there are boundary seals about 18 inches above grade. There are no other fittings below the seal. The conduit crosses the facility and comes back up also in a class 1 Div 2 area. It dead ends about 18' in the air at a cable tray. It is open to atmosphere at the tray.
That 18' run could be a bit of a problem.
To start see Section 501.15(B)(2). The boundary seals at either end don't need to be
explosionproof. See the last two sentences in Section 501.15(B)(2). That takes care of the process end.
Let's look at the cable tray end. This is where the 18' could be iffy. Technically, the "real" boundary is at grade and the seal belongs within 10' of it. The conduit to tray transition is covered by Exception No. 2 so you don't need two [edit add:] boundary seals on that end. I personally wouldn't worry about the coupling needed between the two (or more) conduit sections, especially if I used a single continuous 18' section - but the Code is the Code and 10' is the limit.
Just curious, which Application, Section 500.7(K)(2), (K)(3), or (K)(4) are you using to justify the gas detection system?
