Instrumentation & Control Equipment Environmental Conditions

The environmental conditions in which I&C equipment must operate or which can affect the proper or continued operation of I&C equipment shall be clearly identified and considered in I&C design and equipment selection.

Normal ambient, abnormal operating, climatic and event conditions shall be evaluated in the identification of applicable environmental conditions.

Guidance: The environmental factors that should be considered when selecting equipment location or equipment for a location include, but are not limited to, the following:

  1. Temperature and/or Humidity Extremes
  2. Barometric Pressure Variations
  3. Airflow
  4. Corrosive Atmospheres
  5. Area Flooding
  6. Acoustic Noise
  7. Electronic Noise, or Electromagnetic Interference (EMI)
  8. Power Supply Quality (electrical surges, frequency variations, etc.)
  9. Grounding
  10. Lighting
  11. Lightning Protection
  12. Physical Security
  13. Vibration
  14. Interference from Large Motors and Power Feeders
  15. Chemical and Particulate (dust) Contamination
  16. Radiation
  17. Elevation above sea level

The I&C equipment that is required to meet performance specifications may necessitate a specific type of environment, or in other cases, the environment may limit the choice of equipment. Where I&C equipment cannot be found that will provide the required performance in the environmental conditions present, equivalent alternate method shall be provided such as heated, cooled, waterproof, corrosion protective and similar enclosures. For enclosures or other environment protective devices, their effect on equipment performance, ability to test, and effect on calibrations shall be evaluated.

All environmental restrictions imposed by the manufacturer of the equipment shall be met. If several types of equipment are to be located within the same environment, the environment must satisfy the most restrictive of all the equipment specifications.

Guidance: In extreme cases, the equipment climate may require very close control over all environmental aspects. In some instances, sensitive equipment may be placed in a sealed enclosure, so that only a relatively small volume would need to be protected. The more rugged equipment, such as programmable controllers, industrialized PCs, or MIL-Spec equipment, can usually be installed and maintained under the existing ambient conditions. Hazardous areas may necessitate the use of intrinsically safe equipment, explosion-proof enclosures, sealing and purging, etc.

If I&C equipment is to be located in Class I, Divisions 1 and 2; Class II, Divisions 1 and 2; or Class III, Divisions 1 and 2 locations, where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitable fibers, then the requirements of NFPA 70 (NEC) – Articles 500 through 504 shall be met.

Guidance: ANSI/ISA-RP12.06.01, “Wiring Practices for Hazardous (Classified) Location Instrumentation – Part 1: Intrinsic Safety”, provides guidance in the design, installation, and maintenance of intrinsically safe I&C systems for hazardous (classified) locations. This recommended practice should be used in conjunction with the requirements of Article 504 of the NEC.

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