 Tests Four tests were repeatedly performed as well as an additional questionnaire on comfort and general condition before the tests started and after every four-test-series. Test I comprised correct assembly and position of coloured and numbered 2 mL tubes and screwcaps in a storage device to test fine motor skills, concentration and error rate. Test II checked the same skills in a different approach by pipetting different volumes of coloured water into a 96-well microliter plate according to a given pattern. Test III d2 Test of Attention is a timed test of selective attention and a standardized refinement of a visual cancellation. In response to the discrimination of similar visual stimuli, the test measures processing speed, rule compliance, and quality of performance, allowing estimation of individual attention and concentration performance. Test IV investigated reaction time, mobility, speed and physical exercise by tapping touch sensors directed by signs on a screen tapping test by talent-systems sportconsulting Gmbh, All subjects performed the tests after randomisation of the starting exercise. For example, subject one started with test I while subject two started with test II at the same time. After ten minutes testing time and a five minute break, subject one carried on with test II and subject two with test I. After a five minute break, subject one started with test III while subject two performed test IV over a 10 minute period. Again after five minutes break, subject one continued with test IV and subject two with test III. Subjects documented their individual comfort and general condition in a structured questionnaire before the tests started and after every series of tests. All four tests were repeated 6 times at 22C 6 hours total working time on the first test day and four times at 28C 4 hours total working time on the second test day. Limiting factors for working conditions were ranked after every series from 1 to 10 on the questionnaire whereby ranking 10 was a reason for terminating the study. Heart rate HR was measured with a wireless heart rate monitor placed below the sternum directly on the skin Garmin Forerunner 305 before and after the test series data used for statistical analysis and additionally recorded during the test series. Body temperature and body weight were measured as well as weight of the respective PPE for calculating dehydration and evaluation of heat stress. 