What are the specifications for instrument cables in oil & gas plants? Is it necessary for them to be flame retardant ? and for ESD cables, is it necessary to be fire resistant?

yes to both questions, ESD (emergency shut down) try looking at NEK6006, Noskab UKOOA type for Instrumentation, general control and Eland FTP type for fire sensors gas monitors.

Please, don't forget to check the electrical specifications in force at the installation site.

Instrument cable specifications for Oil & gas depends on the client’s minimum requirements for the design, manufacture, testing & supply.

Here are some examples of general specifications;

Signal Cables, Single pair or triple, Multi pair or Multi triple,

Grade=300/500volt, Sheath= PVC or CSP, Armour = Steel galvanized wire, Tape= A tape bearing the approved manufacturers name and year of manufacture to be laid under or over the core wrapping, Bedding = TPE, Overall screen = Aluminum backed mylar tape, Drain wire = Copper wire under and in contact with the screen running the full length of the cable, Core insulation = PVC or EPR or XLPE, Conductor = 1.5mm2 stranded annealed tinned or bare copper, Twists = 6-8 twists per foot

Solenoid valve & small power cables, Single pair, Multi core or Multi pair,

Grade=600/1000volt, Sheath= PVC or CSP, Armour = Steel galvanized wire, Tape= A tape bearing the approved manufacturers name and year of manufacture to be laid under or over the core wrapping, Bedding = TPE, Core insulation = PVC or EPR or XLPE, Identification = Color red/black, Conductor = 2.5mm2 stranded annealed tinned or bare copper, Twists = optional

Thanks for your attention.
another question is:
Is it recommended that Low Smoke Zero Halogen cable used for Instrument cables?

I heard about the LSZH although I don't have experience yet using it, LSZH has an advantage over PVC in terms of during fire, it has a low smoke property, PVC burn & melt in the fire, LSZH cable will also burn but it don't emit heavy smoke and toxins. LSZH has a restriction in temperature range of -20degC to 75degC compare to PVC has a temperature range of -50degC to 90degC.LSZH cable is also more expensive than PVC counterparts.