Thermal comparisons between two uniform systems and its impact on occupational health: A Pilot Study

Such exposures must be considered as heat stress can impact occupational performance. The aim of this pilot study was to compare the effects of heat (both subjectively and objectively) on the wearer under two different clothing and vest systems.

A cross over trial was conducted with two participants acting as their own controls.

Participants entered a 38-45°C dry sauna where they stood for 20 minutes wearing one of the two randomly allocated ‘skin out’ (i.e. clothing and vest) configurations :

GEN1: Shirt: Woven = 55% Cotton, 45% Poly, Knit = 40% Modacrylic, 33% Cotton, 20% Viscose, 7% Lyocell. Trouser: 65% Polyester, 35% Cotton. Vest: GD Variant with 2x Armour Australia F/B training plates. 

GEN2: Shirt: Woven = 65% Polyester, 35% Cotton, Knit = 42% Outlast, 41% Polyester, 1.5% Silver yarn, 15.5% Elastane, Mesh = 100% Polyester. Vest: GEN2 Variant with 4x Armour Australia training plates (2x F/B, 2 x side). 

Measures included: body weight (kg), tympanic temperature, skin (forehead), clothed chest, under surface and outer surface of the vests (°C), subjective ratings (scale 1-10 for thermal general and under clothing, sweatiness, discomfort & comfort, and a mannequin sketch with a Visual Analogue Scale). An infrared camera (FLIR ONE) was used to capture thermal images.

Tympanic was higher than forehead temperature (mean=38.55 ± 0.18*C v 34.78 ± 2.36*C) = Thus it is purported that heat was trying to escape the body following the 20min exposure. The inner surface of the vests for GEN2 was markedly cooler post exposure when compared with chest temperature post-exposure (-2.9*C) when compared to GEN1 (-1.4*C).  Allowing heat to transfer away from the chest(hotter) to the vest(cooler). The difference in heat between the outer surface and inner surface of the vests was greater in GEN2 (See Fig 2) = heat transfer from outer surface to inner surface is slower. Across all subjective measures GEN2 scored more positively than GEN1 with lower VAS scores and fewer negative comments on the mannequin sketch. Heat dissipation suggests that GEN2 held less heat around the chest but held more heat around the legs – the latter may be through distribution of heat away from the torso.

GEN 2 appears to better protect the wearer from external environment heat transfer and better distribute heat away from the wearer. 

Return to work programs for police officers must consider how their uniforms and PPE contribute heat stress and how this can impact occupational performance.