PDT Instrments in safe area

[spbdasan]

Hi Experts,

In our design we need to choose room pressure differential transmitters(PDT) with following conditions
Here the areas have been classified into two, outside as Hazardous area (Zone 1) and the Room as safe area. Now,PDT instrument is going to place inside the room, to monitor the positive pressure compare with hazardous area (outside) and my client insists us to use safe area PDT instead of Ex-proof.
In this case can we use normal transmitters in safe area?

 

[rbalex]

Hi Experts,

In our design we need to choose room pressure differential transmitters(PDT) with following conditions
Here the areas have been classified into two, outside as Hazardous area (Zone 1) and the Room as safe area. Now,PDT instrument is going to place inside the room, to monitor the positive pressure compare with hazardous area (outside) and my client insists us to use safe area PDT instead of Ex-proof.
In this case can we use normal transmitters in safe area?

Your description is NFPA 496 "Type X" pressurizing.

If you are designing to IEC Standards your client is correct. If you are designing to the most recent NFPA 496 Standard, your client may be correct, depending on whether the room is a "control room" or not. A control room "Type X" requires: "For Type X pressurizing, a cutoff switch shall be incorporated to de-energize power automatically from all circuits within the control room, not approved for the external area classification, upon failure of the positive pressure air system." [Section 7.4.5] This would include the "PDT". Other rooms only require the device to be suitable for the classification where they are installed. [Section 4.11.1.2]

This is a good example that IEC Zone 1 is actually a glorified NEC Division 2.(Which would use NFPA 496, "Type Y" pressurizing/purging)

 

[spbdasan]

Hi rbalex,
yes ours is IEC, we are using normal type temperature transmitters in safe area, but afraid to use normal PDT in safe area because of process line. as per supplier comment incase diaphragm seal failed there is severe damage in the instruments.

if our thinking is wrong pls correct us.

 

[rbalex]

I no longer have access to the latest IEC Standards and it has been 15 years or more since I worked an IEC project. Still, enclosed piping, including the PDT line would not need independently classifying the room, especially a pressurized one.

My guess (note guess?) is your client is still correct.