Which scenario is least likely to lead to positional asphyxia?

Positional asphyxia occurs when a person is unable to breathe due to their position, often resulting from compression or a lack of airflow. When a subject is lying flat on their back with no restraints, their diaphragm and thoracic cavity are in optimal positions for breathing. This posture allows for effective chest expansion and the ability to inhale and exhale freely. As a result, individuals can usually manage their airflow and do not experience the same risks associated with more restrictive or prone positions.

In contrast, the other scenarios involve body positions that can impede respiratory function. Sitting in a slumped position can compress the diaphragm and restrict lung expansion. Being placed face down in a confined space presents obvious challenges to breathing, as this position often leads to reduced airflow and potential airway obstruction. Similarly, holding a subject in a prone position with resistance can compromise their ability to breathe due to physical pressure and potential muscle fatigue. Thus, the first scenario, with the individual on their back and unrestrained, is least likely to lead to positional asphyxia.