Peak limitation: Limitation of exposure peaks and short-term exposures [MAK Value Documentation, 2011]

The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area sets maximum concentrations for chemicals in the work place air (MAK value). The MAK value is defined as a time‐weighted average concentration for 8 hours per day and assuming on average a 40‐hour work week. The Commission has defined criteria to limit exposure peaks which commonly occur at the work place to avoid possible adverse health effects. Peak exposures are limited by an excursion factor, which, when multiplied with the MAK value, gives the maximum permissible peak concentration as average of a sampling period of 15 minutes. Such excursions are restricted to 4 times per shift and should be spaced at least by a one‐hour interval. Compounds which act primarily locally, i.e. irritants of eyes or airways as well as respiratory sensitizers, are grouped into Peak Limitation Category I. For these chemicals, the concentration is decisive for the effects. The default excursion factor is 1, if human data on local irritation or suitable long‐term animal studies are available, a higher factor can be set. An excursion factor of 1 means, that at any time during the shift, the 15‐minute average must not exceed the MAK value. In specific cases, a momentary value can be set, i.e. a concentration that must not be exceeded at any time. When systemic effects are critical, the compound is assigned to Peak Limitation Category II. As default, it is assumed that the systemic maximum concentration is exposure limiting. The impact of an exposure peak on the maximum concentration is dependent on the half‐life of the chemical. The default excursion factor is 2, if data on the half‐life of the chemical or its critical metabolite are not available. When the half‐life is known, corresponding excursion factors have been estimated with a kinetic first‐order model to limit the increase of the maximum systemic concentration to less than 25%. For half‐lives ≥ 8 hours, 4–8 hours, 1–4 hour and < 1 hour the respective excursion factors are 8, 4, 2 and 1. When it is shown that the critical effect is not caused by the concentration (Cmax) but by the concentration‐time product (area under the curve), the excursion factor can be up to 8, which is the maximum possible excursion factor. However, the resulting short‐term concentration must not lead to irritation or narcotic effects. Regardless of the magnitude of the excursion factor, the MAK value, i.e. the average over 8 hours, must not be exceeded