Based on the principle of “equal work,” the conventional, energy equivalent approach of rating physical environmental exposures – which is derived from physics rather than physiology – is presented. Straightforward examples demonstrate the difficulty of summarizing exposure intensity and duration under human-physiological aspects. Results from experiments with continuous noise exposures of different time structures confirm that an energetically equivalent noise exposure does not correspond with equal “costs” for the human hearing. The energy equivalent rating according to national and international standards as well as the Accident Prevention Regulation “Noise” (UVV Lärm) or the cut-off level diagram is questionable at best, but may even be dangerous.