Occupational Heat Stress on Workers' Productivity

The participants followed the study protocol which included, one work shift of sham measurements, one work shift business as usual and four (4) different scenarios (interventions) on different work shifts. Apart from the sham measurements the rest of the scenarios were tested in a random order for different participants.

1. Work/ rest scenario: The participants were asked to take planned breaks in the shade during their work shift. The amount of breaks taken ranged between 3 and 10 minutes every hour depending on the current work duties of the employees.
2. Hydration scenario: The participants were advised (not forced) to drink minimum of 750 ml of water or ice - slushies, every hour during their work shift.
3. Clothing scenario: The participants were randomly provided with different types of clothing, i.e. white breathable coveralls, ventilated garments and breathable uniform with water submerging parts, to wear during their work shift.
4. Assisted labor: The participants in agriculture, that were carrying heavy weights were provided with "e-carts" (automated carrying vehicles), during their work shift.

Baseline data [self-reported age; body stature (Seca 213; seca GmbH \& Co. KG; Hamburg, Germany) and body mass (BC1000, Tanita corporation, Tokyo, Japan)] were collected one day prior to the measurements. Medical history of all the participants was recorded. During the field study, continuous heart rate, core temperature and mean skin temperature data were collected using wireless heart rate monitors (Polar Team2. Polar Electro Oy, Kempele, Finland), telemetric capsules (BodyCap, Caen, France), and wireless thermistors (iButtons type DS1921H, Maxim/Dallas Semiconductor Corp., USA), respectively. Skin temperature data were collected from four sites (chest, arm, thigh, and leg) and were expressed as mean skin temperature according to the formula of Ramanathan (Tsk = [0.3(chest + arm) + 0.2(thigh + leg)]). Furthermore, continuous environmental data [air temperature (°C), globe temperature (°C), relative humidity (%), and air velocity (m/s)] were collected using a portable weather station (Kestrel 5400FW, Nielsen-Kellerman, Pennsylvania, USA). Urine samples were collected at the start and the end of the work shift to evaluate the hydration status of each worker. Urine specific gravity was assessed for each urine sample using a refractometer (PAL-10S, ATAGO CO., LTD., Fukaya, Saitama Prefecture, Japan) and was classified as either hydrated (< 1.020) or dehydrated (≥ 1.020). In addition, urine colour was assessed using a urine color scale. Questionnaires were used to assess workers' perception on exertion (Borg scale), thermal comfort/sensation, humidity comfort/sensation, radiation comfort/sensation, wind speed comfort/sensation, skin wetness, sleepiness, physical demands of the workload. The Heat Strain Score Index (HSSI) was used to assess the perceived heat strain of the workers.

Video cameras installed in close proximity (about 40m) to the workers were used to assessed workers labour effort. Video recordings were analyzed on a second by second basis using time-motion analysis method. Importantly, when video cameras were not feasible to be installed real-time task analysis was used to examine workers capacity for manual labour. For that reason, an android-based application (FAME_TASK App) was used to record the tasks of the workers on a second by second basis. The App was continuously monitoring the work time spent on irregular work breaks (unplanned breaks), the duration of uninterrupted work and the time spent as lunch time or other breaks provided by management (planned breaks). The unplanned break was divided into two categories: the breaks during which the workers decided to rest in the shade (unplanned break under the shade) and the breaks during which the workers chose to stay under the sun (unplanned break under the sun). Also, the uninterrupted work was divided into nine categories: work in an outdoor environment with a low metabolic rate; work in an outdoor environment with a moderate metabolic rate; work in an outdoor environment with a high metabolic rate; work in a mixed (outdoor and indoor) environment with a low metabolic rate; work in a mixed (outdoor and indoor) environment with a moderate metabolic rate; work in a mixed (outdoor and indoor) environment with a high metabolic rate; work in an indoor environment with a low metabolic rate; work in an indoor environment with a moderate metabolic rate; work in an indoor environment with a high metabolic rate. The labor effort (i.e., low / moderate / high metabolic rate) was defined according to the ISO 8996:1994 as low, moderate and high metabolic rate. Based on these definitions, the recorded tasks were fourteen. During the work-shift, a researcher was following each worker, monitoring them with the FAME_TASK App, until they end of their work shift.