IEC 60721-3-4:2019 classifies groups of environmental parameters and their severities to which products are subjected when installed for stationary use at non-weatherprotected locations. Weatherprotected locations where products can be mounted for stationary use permanently or temporarily are addressed in IEC 60721-3-3.This third edition cancels and replaces the second edition published in 1995 and Amendment 1:1996. This edition constitutes a technical revision.This edition includes the following significant technical changes with respect to the previous edition:a) Clause 1: reworded.b) Clause 2: normative references have been updated.c) Clause 3: definitions have been updated.d) Clause 4: reworded and simplified.e) Clause 5: revised and updated. Several classes have been replaced by completely new classes based on the use of new information obtained from referenced technical reports.f) Defined values of chemically active substances are now by reference to ISO 9223.g) Tables 1 through 5: updated.