ISA 71.01 : 1985

1 Purpose
2 Scope
3 Introduction
4 Definitions
  4.1 Normal operating conditions, operative limits, and
      transportation and storage conditions
  4.2 Maintenance conditions
  4.3 Maintenance
5 Location classifications
  5.1 Air-conditioned locations (class A)
  5.2 Enclosed temperature-controlled locations (class B)
  5.3 Sheltered locations (class C)
  5.4 Outdoor locations (class D)
  5.5 Special locations (class X)
Appendix A - Psychrometric charts

ISA-71.01-1985, Environmental Conditions for Process Measurement and Control Systems: Temperature and Humidity, defines standardized classifications for temperature and humidity conditions affecting industrial process measurement and control systems. This standard organizes environments into classes based on location types such as air-conditioned, enclosed temperature-controlled, sheltered, outdoor and special locations. It assigns severity levels that specify ranges and tolerances for temperature and relative humidity for each. This standardization helps in selecting or designing equipment suited to specific environmental conditions by providing clear, consistent criteria for operation, maintenance, storage and transportation scenarios. It supports communication among manufacturers, users and engineers by offering a common language and reference for environmental requirements, facilitating better alignment of equipment performance with real-world conditions encountered in various industrial settings.