According to ISO 7730:2005, classification is a mandatory precondition for thermal comfort assessment since the appropriate criterion depends on which category the specific work situation (SWS) investigated belongs to. Unfortunately, while the standard does include three different comfort criteria, it does not indicate how the appropriate criterion should be selected. This paper presents a classification scheme that allows thermal comfort assessment to be reliably performed in any environment. The model is based on an algorithm that calculates a score by means of a weighted product of three quantities, each one taking care of a specific, highly relevant element: the subject's thermal sensitivity, the accuracy required for carrying out the task and the practicality of thermal control. The scheme's simple modular structure can easily accommodate both changes and additions, should other hypothetical elements be identified to be as relevant to the classification scheme. The model presented allows a modulation of comfort levels across different social groups. It is so possible to provide extra care for children, elderly, pregnant women, disabled and other 'weak' categories, as required by ISO/TS 14415:2005, by setting the highest comfort level. Finally, it also widens the options for simultaneously establishing comfort conditions for different individuals performing different tasks in the same area and clarifies whose comfort should be pursued with the highest priority.

As a part of their very wide range of applications, international standards also represent an excellent technical support to the legislation on comfort and health at the workplace. The existing standards on thermal comfort and on indoor air quality both include limits of acceptability which strongly depend on the category chosen for the investigated work environment. Therefore, the same situation can easily meet compliant or largely exceed specified limits depending on which category is applied. Unfortunately, no clue is currently provided on how to select the appropriate category, and the enduser is left uninformed. In this paper, we present a method to assign limits of acceptability to any work situation whose thermal comfort and indoor air quality must be assessed. The method extends previous work developed specifically for thermal comfort and is based on an algorithm which takes into account three quantities that provide a comprehensive description of the work environment, the activity which is carried out and the sensitivity of individuals. The scheme's simple modular structure can easily accommodate both changes and additions, should other hypothetical elements be identified to be as relevant to the classification scheme.

The implementation in technical standards on heat stress assessment of two new thresholds is recommended. The lower threshold, to be set at tcore ≅ 37.1 °C, is aimed at ensuring that the subject is able to carry out demanding mental tasks without appreciable performance loss, while the higher threshold, to be set at tcore ≅ 37.2 °C applies to simpler tasks.