Protection for Instruments and Solenoid Valves in Hazardeous Area

Your instrumentation engineer should know this. If they don't, they should. The site safety officer might know.

Finally, if all else fails, the instrumentation supplier should know what your requirements are, if your instrumentation engineer is worth his pay. They have the responsibility to get it right.

We're just an anonymous forum who can't see anything at your facility.

Hire an engineer or tech who knows how to specify instruments.

lyn is correct, your dealing with an area that requires extreme caution when installing any equipment. You should have an engineer who has experience, not only in designing equipement for use in, but also has hands on experience working in, hazardous classified areas. That said, I will give you some info, which is from the NEC, regarding the area, you stated, you're dealing with. According to you, it is a Zone 1, Group IIB, Temp class T3 (200C/392F). Per the NEC, 2011, this would be a Class 1, Zone 1, IIB area. Per the NEC this is an area that contains 'acetaldehyde, ethylene, or flammable gas, flammable liquid-produced vapor, or combustible liquid-produced vapor mixed with air that may burn or explode, having either maximum experimental safe gap (MESG) values greater than 0.50 mm and less than or equal to 0.90mm or minimum igniting current ratio (MIC ratio) greater than 0.45 and less than or equal to 0.80. For those familar with NEC classes, Class 1, Zone 1, Group IIB is equivalent to a Class I, Group C, area. A Temp class of T3, requires the equipments max surface temp be = or < 200C. That said, per the NEC, 'Electrical equipment designed for use in the ambient temperature range between -20C and +40C shall require no ambient temperature marking. Your question was 'should I use an Exd or Exi rated device' for instruments and solenoids. Acceptable protection techniques for Class 1, Zone 1, IIB area (specifically) are: Flameproof "d", "db", Increased Safety "e". "eb", Intrinsic Safety "ib", Encapsulation "m", "mb", Oil Immersion "o", "ob", Pressurization "px", "pxb", "py", "pyb" and Powder Filled "q", "qb". I could've saved myself alot of typing, but I hoped by including this 'small' amount of information, which goes into the design process, for hazardous areas, you might see why we will not tell you, specifically, what equipment rating you should use. As stated in the NEC 505.7(A) Classification of areas, engineering and design, selection of equipment and wiring methods, installation, and inspection shall be performed by qualified persons.' I mean no disrespect, but that you have to ask, proves you do not fall into that category. While there are some in this forum, more than qualified to design eq for these areas, we cannot do so based on just the info you provided. There are many other considerations, which come into play in the design, specification and installation, of equipment in these areas. As such, no one here, should give you a direct answer. Hopefully, this will encourage you to seek a profession engineering firm or at least contact the engineering departments of the equipment manufacturers, you are dealing with. Companies such as Rosemount (Emerson Process), ASCO, and others have excellent tech and engineering support services. Hope this in some way gets you on the path to a safe and productive installation.

@ Bfmickl Thanks for the info

It's all in IEC 60079. Read further!