Figure 2.

Relationships between the need for heat loss (positive values) or heat gain (negative values) to reach thermal equilibrium ($E_{req}$, x-axis) against the potential evaporative heat losses given a set of environmental conditions and clothing insulation ($E_{max}$, y-axis). The ratio of $E_{req}$-to- $E_{max}$ relates the degree of thermal stress to heat exerted on the body (required skin wettedness, ${\omega }_{req}$). Critical values of ${\omega }_{req}$ are represented with black lines: 0.5 for low-efficient heat loss (thick line) and 1 to limit compensable/uncompensable heat stress (thin line). The purple lines represent values of $E_{max\mathrm{\_}sweat}$ for the young/acclimatized and elderly/non-acclimatized when the liquid sweat loss is non-replenished. The vertical gray line at $E_{req}$ = 0 indicates thermal equilibrium. Therefore, the numbered zones correspond to 1) cold stress, 2) compensable heat stress (CHS), 3) CHS with low sweating efficiency (CHS + Low $S_{eff})$, 4) uncompensable heat stress (UHS), 5) CHS with limited sweat rate (CSH + LS), and 6) CHS + Low $S_{eff}$+ LS.