using liquid-tight in Class 1, Div 1 location

[wire rat]

On our most recent Wastewater treatment project, we were told by the Inspector that in any Class 1, Div 1 location, Explosion-proof liquid-tight must be used at all motors, heaters, solenoid valves etc. I havent been able to find this in the NEC. Is this required. I know that Appleton makes what they call "flexible couplings" Is this considered Explosion-proof liquid-tight.
Once we are successful in getting a new Wastewater treatment project, we are often invited to the engineering companys last project. On a recent visit to their latest project I noticed that they used regular liquid-tight in a Class 1, Div 1 location. Was this an oversight by that projects Inspector?

[rbalex]

There is no such thing as "explosion-proof liquid-tight flexible conduit," and yes the Appleton flexible coupling and similar products made by other manufacturer's are what many folks erroneously believe is explosion-proof liquid-tight.

Standard LMFC is not suitable for Division 1. Listed flexible fittings (couplings) are permitted, but not required – See 501.10(A)(2)

Edit Corrected a typo in the reference

[justdavemamm]

We use "Metallic Flexible Conduit", ie Sealtite, for Intrinsically Safe items in a Class I, Division 1 location. That would include solenoids.

For some motors we use Crouse-Hinds ECGJH136 flex or equiv. Perhaps that's what the OP Inspector was referring to. But it's expensive.

[rbalex]

The ECGJH series are "flexible couplings" and acceptable in Division 1. It isdifficult to imagine applying intrinsically safe wiring methods to motor circuits.