I think it could be done with a rated, purged enclosure, but the HMI would have to be inside the enclosure, and you view it via window. Need to check with your local experts.
The enclosure is purged for a set period before power is applied, once power is applied, it pressure drops below a minimum value, the power is removed before explosive vapor can enter.
You want to make sure what ever system you use is approved/certified by a third party. In the US, this would be FM or other authority. It's going to be expensive.
I think it would be more cost effective to have the PLC in a safe area and use Profibus PA (intrinsically safe) for field devices. The HMI would still be a challenge.