Abstract
Half-mask respirators have been increasingly used in public facilities to protect against indoor air contaminants. However, when they are used, the respiratory heat flow is restrained and its release into the environment is limited. This study evaluated the thermal burden on respirator users in an indoor environment where a significant heat load from hot-and-humid air is introduced. Twenty-five participants walked on the stairs at a speed of 4.6 km/h wearing a filtering facepiece respirator (N95 mask) or elastomeric facepiece respirator under varying air temperatures and relative humidity (RH). The thermo-physiological properties on the nasal, facial, and forearm skin and the temperature/RH of the breath were evaluated. Thermal sensation was also surveyed. The results showed that a thermal microclimate was developed inside the mask, with the heat index in the microclimate of N95 masks being elevated to 61.2–67.9 °C and a risk level of “Extreme Danger”. The metabolic heat from respirator use shifted the paradigm of thermoregulation to a scheme involving localized enhancement in thermoregulation. When using N95 masks the skin moisture level was increased by 77%–588% and the transepidermal water loss by 18%–72%. Thermoregulation underlying heat strain was near-saturated at 33 °C, and an abrupt increase of 1.6- to 3.6-fold in thermal sensation was concurrently observed. The threshold-controlled increase in sensation was likely a result of the thermal strain capacity being overwhelmed. These findings demonstrated that even under room temperature, caution should be exercised when using N95 masks for performing tasks of moderate metabolic load.
Published Version
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