Using the procedures published in ISO / TR 11079 Evaluation of cold environments - Determination of required clothing insulation (IREQ), an estimate of the Duration Limited Exposure (in hours of Exposure) as a function of Ambient Temperature can be created for the ensemble at various levels of activity (i.e., metabolic rate). This can be seen in the following Chart.
Factors held constant in construction this comparison are:
- 0.5 clo of other clothing worn (clo values in chart are for the ensemble alone, but the relationship between time and temperature has been adjusted to include a base layers of clothing)
- Mean Radiant Temp assumed to be the same as Ambient Temp (usually the case).
- 65% Relative Humidity
- 0.4 m/s (0.9 mph) Relative Wind Speed
- 8.0 l/m²s Air Permeability (Slightly more than “Low”)
- 0.6 m/s Walking Speed
- 0.0 W/m² Rate of Mechanical Work (normally the case).
This graph indicates that the ISO / TR 11079 analysis predicts that the insulated ensemble will be indefinitely comfortable at a temperature of -8 °F when performing “Moderate Work”, if a person is adequately insulated over the balance of their body -- but this is NOT a guarantee. Keep in mind however that every person is different and that some people will need more insulation than others for the same level of exposure conditions.