In many states, the permit states that the opacity shall not exceed what percentage except for a specified time duration?

The selected answer indicates that in many states, the permit limits the opacity of emissions to not exceed 20% for a specified duration. Opacity refers to the measure of how much light is blocked by smoke or other emissions, and regulating it is crucial for air quality management.

The limit set at 20% means that emissions from a facility must be sufficiently controlled so that no more than one-fifth of light is obscured, which is an important factor in assessing the environmental impact of emissions from crematories and other facilities involved in the handling of human remains. Adhering to this limit helps ensure compliance with air quality standards designed to protect public health and the environment.

In many areas, this percentage is a common guideline enforced by environmental regulatory agencies, aiming to balance operational needs with the necessity to minimize pollution.