🌿 Cold thermal environment — the required clothing insulation IREQ

Environment PN-EN ISO 11079

Overview

The standard specifies methods and strategies for assessing the thermal stress associated with exposure to a cold environment. They are applied to continuous, intermittent and occasional exposure and to various kinds of work, indoors and outdoors; they do not cover the effects of particular meteorological phenomena (e.g. precipitation), which are assessed by other methods. Cold stress is assessed in two ways: as the general cooling of the body and as the local cooling of the individual parts of the body (the extremities, the face) — convective (wind chill), conductive, of the extremities and of the respiratory tract.

For general cooling the standard gives an analytical method based on the calculation of the heat exchange of the body, of the clothing insulation required (IREQ) to maintain thermal equilibrium and of the insulation provided by the clothing used or planned. The IREQ is a measure of cold stress integrating the influence of the air temperature, the mean radiant temperature, the relative humidity and the air velocity for specified levels of metabolic rate; it serves also to specify the requirements for clothing and the selection of clothing for the real conditions and to plan the time and the regime of work in the cold.

In Poland the IREQ index (alongside the WCI) was described by the standard PN-87/N-08009; it was replaced by PN-EN ISO 11079:2008, which is in force (status of the PKN card as of 23.09.2026; the Polish version was published on 27 February 2014), and the classification of a workplace as a cold thermal environment (PMV ≤ −2) is given by the regulation on the maximum admissible concentrations (NDS) and the maximum admissible intensities (NDN).

Method principle

The basis is the general equation of the heat balance of the body: M − W = Eres + Cres + E + K + R + C + S, where the left-hand side is the internal production of heat (the metabolic rate M reduced by the effective mechanical power W, usually negligible), and the right-hand side is the sum of the heat exchange in the respiratory tract (Cres, Eres), by evaporation from the skin (E), by conduction (K), by radiation (R) and by convection (C) at the surface of the clothing, and of the accumulation of heat in the body (S). The equation is solved for the required clothing insulation IREQ = (tsk − tcl)/(R + C) under specified criteria of physiological strain; since it contains two unknowns (IREQ and the temperature of the surface of the clothing tcl), it is solved iteratively. The standard defines IREQmin (the minimal insulation) and IREQneutral (the insulation for the neutral state). The IREQ is compared with the resultant insulation of the clothing used, corrected for the influence of the wind and of movement; if the insulation worn is smaller than that required, the limited duration of exposure Dlim is calculated on the basis of the admissible cooling of the body.

Applications

• Cold stores, freezing stores, refrigerated warehouses, the food industry — assessment of workplaces in a cold thermal environment
• Work outdoors in winter: building, transport, forestry, municipal services
• Selection of protective clothing of the required thermal insulation (in clo) for the given conditions and activity
• Planning of the working time and of the breaks for warming up (Dlim) where the insulation of the clothing is insufficient
• Assessment of local cooling: wind chill, contact with cold surfaces, cooling of the extremities and of the respiratory tract

Key parameters

Standard

Standard number

PN-EN ISO 11079:2008

Title (PL)

Ergonomia środowiska termicznego — Wyznaczanie i interpretacja stresu zimna z uwzględnieniem wymaganej izolacyjności cieplnej odzieży (IREQ) oraz wpływu wychłodzenia miejscowego

Title (EN)

Ergonomics of the thermal environment — Determination and interpretation of cold stress when using required clothing insulation (IREQ) and local cooling effects

Step-by-step procedure

1. Measurement of the parameters of the environment

   At the workplace measure the air temperature, the velocity of the movement of the air and the temperature of the blackened globe and the humidity. Carry out the measurements in the period corresponding to the extreme cold loads, not less often than once every 4 hours; average the results taking into account the changes in time and in the space around the worker.

2. Determination of the metabolic rate

   In the course of the measurements determine the energy expenditure of the persons working — from a measurement of the oxygen consumption or, more simply, from the tables of ISO 8996.

3. Calculation of the IREQ

   From the measured parameters and the metabolic rate calculate the IREQ from the equation of the heat balance (the program from annex F of the standard or the IREQ calculator); determine IREQmin and IREQneutral.

4. Comparison with the clothing

   Establish the resultant insulation of the ensemble of clothing used (ISO 9920, with a correction for wind penetration and movement) and compare it with the IREQ.

5. Assessment and Dlim

   If the insulation worn is smaller than that required, calculate the limited duration of exposure Dlim on the basis of the admissible level of cooling of the body and plan breaks for warming up or select warmer clothing. Assess in addition the local cooling by the methods of clause 6 of the standard.

Required equipment and apparatus

Health and safety (OHS)

• In freezing stores and cold stores the person making the measurements uses protective clothing appropriate to the temperature and limits the time spent there
• Freezing surfaces and ice increase the risk of slipping — secure the passageways
• The batteries of the meters lose capacity at low temperature — control the power supply and record the data as you go

Frequently asked questions