The purpose of this part of IEC 654 is to provide users and suppliers of industrial-process measurement and control systems and parts of such systems with a uniform listing of the selected environmental conditions to which equipment may be exposed in specified locations.

This part lists environmental climatic conditions e.g. air temperature, humidity and air pressure in specified locations to which land-based and offshore industrial-process measurement and control systems may be exposed during operation, during periods when they are installed but inactive and during storage or transportation. Maintenance and repair conditions are not considered.

Environmental conditions directly related to fire and explosion hazards and conditions related to ionized radiation are likewise not considered.

Effects of the specific environmental conditions on personnel are not within the scope of this part.

The influence quantities considered in this part are limited to those which may directly affect the performance of process measurement and control systems. Only environmental conditions as such are considered.

This part establishes location classes with severity levels or sets of severity levels for the environmental conditions listed. Other environmental conditions are covered in other parts of the standard.

The limit values of this part are defined and specified in IEC 721‑3‑3 and IEC 721‑3‑4.

It is intended to serve as a basis for the preparation of comprehensive specifications for environmental conditions by the user and by the supplier.

One of the purposes of this part is to avoid problems which might result from neglecting considerations of specific environmental conditions affecting the performance of systems and parts of systems.

An additional purpose of this part is to aid in the choice of severity levels for use in the development of evaluation specifications of industrial-process measurement and control equipment.