Which of the following is NOT a mode of air delivery for air line respirators?

The correct answer is that constant supply is not recognized as a standard mode of air delivery for air line respirators. Air line respirators typically utilize specific flow modes to ensure that users receive adequate and safe airflow while working in potentially hazardous environments.

Continuous flow refers to a mode where air is constantly supplied to the wearer, ensuring a steady stream, which is crucial in certain settings. Demand flow is designed to provide air only when the wearer inhales, optimizing air usage and allowing for a more efficient supply. Pressure demand systems are utilized where the need for higher protection is paramount, ensuring that air is delivered at a pressure greater than ambient to prevent contaminants from entering the mask.

In contrast, "constant supply" is not a formal term used in this context and does not describe a recognized or standard mode of air delivery. Thus, it distinguishes itself as the option that does not align with the established categories for air supply systems in respirators.