The Assessment of Working Conditions by Chemical Factor with Combined Exposure to Harmful Substances

The variety of chemical compounds contained in complex mixtures and various chemical substances circulating in the workflow conditions potentially highly hazardous chemical impact on workers. Long-term studies indicate the need to take into account the combination of harmful substances with the summation effect when evaluating the chemical factor, which is often not conducted in practice. When assessing working conditions by chemical factors, various combinations of substances with potentially increasing impact on bodies of workers engaged in styrene production and thereby worsening the working conditions have been considered: with similar chemical structure and equal biological impact. During a shift at a workplace, the most common situation is when the excess of concentration of each of harmful substances in the air might not be registered, therefore, working conditions are assessed in such case as acceptable, which objectively does not reflect the potential risk of damage to health caused by chemical factor. It has been demonstrated that, when assessing working conditions by this factor, accounting for the combination of harmful substances of unidirectional impact and summation effect can significantly change the class of working conditions and increase the harmfulness by 1–2 levels. It has been established that with a greater amount of harmful substances contained in the air of the working area and a combined effect of exposure, the permissible limit of summation coefficient will be exceeded even at concentrations significantly lower than those established by standards. This will allow assessing working conditions by chemical factor as a class of greater harmfulness. The above-mentioned implies the need to account for the combined effect when establishing a class of working conditions in order to obtain the objective evaluation of hygienic situation at a chemical production facility.