2007, Piran, Slovenia

Occupational Thermal Problems
of a freezer cooling unit and fan mounted on the ceiling of a custom-made clear Plexiglass
box with insulated arm holes, achieving cooling via convection. Grip strength, tactile
sensitivity, manual dexterity, thermal sensation and thermal comfort were assessed again
following hand cooling. Subjects then performed the cyclical load-lifting task inside the
cooling box. A cold fan was used as necessary to maintain subject hand Tskin between 5-10 o C.
Grip strength, tactile sensitivity, manual dexterity, thermal sensation and thermal comfort
were assessed for a third time following the final lift. After the completion of each trial,
subjects’ hands were rewarmed by immersion in a 35 o C water bath. Throughout the trial, grip
strength was the only assessment performed outside the cooling box.
The lifting task was a continuous vertical oscillation lifting task. Subjects were instructed to
perform a cyclical up-and-down motion of the arm while lifting an object (140 g) that was
mounted with a 6-axis force-torque transducer (Nano F/T 17; ATI Industrial Automation,
Apex, NC, USA), which measured the changes in load force induced by the lifting task as
well as the grip force used to counteract the load forces. The transducer was held using a
horizontal pinch grip, with the pads of the index finger and thumb on the opposing sides of its
surface. For each lift, subjects grasped the force transducer and moved the object up and
down in pace with an auditory metronome (1.53 Hz). The amplitude of the movement was
approximately 20 cm, with the minimum and maximum positions visually marked on the side
of the environmental box.
Three lifts were performed in the vision and no-vision conditions, for a total of 6 lifts per
thermal condition. Lift duration was 15 s, with a 30-60 s rest period between lifts. Maximum
pinch force and minimum slip force, requiring subjects to slowly reduce their grip until the
object slipped out of their hand, were recorded before hand cooling, following hand cooling
(but before the lifts), and following the lifts to determine coefficients of friction across the
conditions.
RESULTS
Target core temperatures were consistently achieved in the warm (+0.5 o C) and cool (-0.5 o C)
conditions (Table 1). Target hand Tskin (