How many degrees of concentration taken at atmospheric pressure does it refer to about permissible concentration of harmful substances in the air of labor working environment?

The correct answer indicates that the permissible concentration of harmful substances in the air of a labor working environment is typically measured at 25°C. This temperature is a standard reference point in occupational health and safety guidelines. It is critical because the concentration of airborne contaminants can vary significantly with temperature. Air density and the behavior of gases change with temperature; hence, establishing a standardized measurement point like 25°C helps ensure consistency in safety regulations and assessments.

At this temperature, the measurements provide a reliable basis for evaluating exposure risks and enforcing workplace safety standards. It is crucial for employers and safety officers to be aware of these standards to protect workers from harmful exposure while working.