Because the global warming of the climate and an aging population who in some countries has to work longer (retirement age to 67 years), the control of heat stress becomes increasingly important.

Heat stress is dependent on environmental factors. But is also strongly influenced by the degree of effort during the work, clothing and personal factors.

Heat stress has negative short-term mental effects: a decrease in vigilance and poorer performance. Under the influence of heat stress more unsafe actions take place and the risk of accidents increases. In working situations, such effects may endanger worker’s own health or that of others.

At core temperatures between 38°C and 39°C the performance of physical tasks slowly decrease, but healthy workers occasionally can tolerate temperatures to around 39°C without problems. However, when the temperature rises above this level, then the health risks rapidly increases. It is unknown what the effect on workers is who are exposed on a daily basis to this temperature stress:  whether the internal temperature will decrease less (by acclimatization) or more (due to excessive stress). If the skin temperature raises above 36 ° C , the physical performance will be limited because the heat transfer from the body core to the skin will become difficult.

Exposure to heat generating sources occurs in many companies and industries.

Employees who by the nature of their work are wearing insulating clothing may also be faced with heat stress (eg. cold store employees, asbestos workers).

Exposure to heat caused by high ambient temperatures will mainly affect employees who work outdoors and in buildings and vehicles where there is a poor climate conditioning.

In the Netherlands no legal limits for heat stress exist. Its enforcement is a set of reference values ​​ for ambient heat used, described in ISO 7243:1989.

Arbo Unie (ECTS) has a unique partnership with the Department of Physiology (Physiomics, Prof. Dr. Maria T.E. Hopman and Dr. Thijs M.H. Eijsvogels) of the Radboud University Nijmegen Medical Centre, for measurements in the human body temperatures. Based on the test findings, occupational hygienists and occupational physicians can give advise on control measures e.g. adjusting the work and rest regime, cooling procedure for furrnaces, protective clothing, drinking advice, advice on medical restrictions, age, pregnancy, drug use etc.

To measure the effects of heat stress for workers the following methods and instruments are available.

The core body temperature is measured using an ingestible temperature pill (CorTemp System; HQ inc., USA). This pill contains a built-in temperature-sensitive quartz crystal and telemetry transmitter, so the actual core temperature can be sent to an external recorder (Figure 1).

Figure 1: Schematic representation of the operation of the temperaturepill (20 mm long and 10 mm wide). The equipment in the pill measures the temperature in the gut. The temperature signal is then transmitted via a telemetric transmitter via radio waves to a remote receiver.   

To measure the skin temperature on the left hand, neck, right shoulder and right shin an iButton (iButton, Maxim Integrated Products, USA) is placed. The skin temperature is then measured every 20 seconds and from the four locations the average skin temperature is calculated using the ISO 9886 standard.

A heart rate belt (Polar Electro Oy, Kempele, Finland) is used to monitor heart rate during the operation. By the estimated maximum heart rate (220 - age) and resting heart rate, the heart rate reserve during the work can be calculated (heart rate reserve = (heart rate during activities – resting heart rate) / (maximum heart rate – resting heart rate)). This variable reflects the exercise intensity during work.

In order to map the pattern of activities during work an activity monitor (SenseWear Armband Pro 3, BodyMedia, Pittsburgh, USA) is placed at the right upper arm. With this bracelet, which uses preprogrammed algorithms and previously entered data one can reliably determine the metabolic equivalents (METs). This is a measure of the intensity of the work.

To evaluate the changes in moisture balance employees are asked immediately before and after work to weigh themselves. When entering or leaving the room the weight is recorded. Changes in body weight are thereby largely identical to changes in moisture loss.

With PIMEX (PIMEX stands for Picture Mix Exposure) may be the effect of practice and workplace conditions on exposure to heat stress and physical exercise in a video screen display. An ideal communication tool and instructional tool.

For more information please contact Fred van Kolck, +316-525 01624, fred.van.kolck@arbounie.nl