Keeping Cool, Even When the Heat Is On: Guidelines and Limit Values to Improve Protective Clothing for Hot Working Environments

In many industries such as steel and glass-making, or mining, working in a hot environment is just part of the job. In order to be able to approach the heat source without risking damaging their health, workers have to wear heatproof and non-flammable protective clothing.

Hitherto, the main focus when designing this protective clothing for the workplace has been ensuring that it is as effective as possible. How comfortable it is to wear and whether the wearer feels good in it are often of secondary importance.

However, especially in high ambient temperatures, a lack of physiological comfort, i.e. inadequate heat and moisture management in protective clothing, can have serious implications for the performance and health of workers.

Scientists at the Hohenstein Institute in Bönnigheim are currently trying to correct this deficiency and, as part of a research project (AiF No. 16782 N), are working on establishing limit values and design principles which could be standardised in order to optimise protective clothing systems for use in hot industrial working environments.

The research project, which is expected to be completed by November 2012, is concentrating on protective clothing for the iron and steel industry. It excludes cases of extreme heat where workers are close to high-temperature furnaces, in which temperatures can reach over 2000°C. Special protective clothing has to be worn when working in this area, and for safety reasons the protective function is a far higher priority than comfort.

The aim of the research project is to extend the existing DIN EN ISO 11612 ‘Clothing to protect against heat and flames’ and include procedures and limit values for measuring physiological properties, taking account of such factors as the ambient temperature, different stress levels, duration of exposure and basic thermal insulation. The main focus of the investigation is the ability of the textile materials that are being processed to carry away sweat. Great importance is being attached to the composition of layers of clothing, consisting of outer wear and underwear, which need to be coordinated in terms of how they transport heat and moisture.

Until now, only the outer clothing in hot working environments has been taken into account. The underwear that is worn is not standardised and at present can be chosen freely by the worker.

The manufacturers of protective clothing for hot working environments – mainly small and medium-sized companies in Germany – will benefit greatly from the results of the research.

Introducing standardised parameters will also lead to increased safety for workers who are exposed to high temperatures every day. If they are subjected to less heat stress, there is less risk of them becoming ill, their performance improves and so too does the company’s productivity.

As a result of this investigation, the Hohenstein researchers expect that, on the basis of their fundamental research, it will be possible greatly to improve the thermophysiological properties of protective clothing without having a detrimental effect on its protective function.

The effects of high ambient temperatures on the human body

If unsuitable clothing is worn in high ambient temperatures, this can disrupt the natural thermoregulation of the body. The core body temperature can then rise above the norm of about 37°C. In the long term, this stress can cause considerable discomfort and strain on the circulatory system, representing a significant health risk. In extreme cases there is a danger of circulatory collapse and then death. There is also a serious risk of heat cramps and heat exhaustion.

The human organism has various ways of regulating too high a core body temperature. However, if the ambient temperature is nearly the same as that of the skin, i.e. approx. 32 °C, evaporating sweat is the only way the body can deal with excess heat. That is why good heat protection clothing must have appropriate moisture transport characteristics. If the wearer is sweating heavily, the textile material must be able to buffer the increased volume of sweat that is given off (in the form of vapour or liquid). Large quantities of sweat have to be absorbed effectively and carried away from the body.

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