Final answer:
The qualitative negative respirator fit check requires gentle exhalation to test the seal. During exhalation, surface tension in the alveoli creates positive pressure to force air out.
Step-by-step explanation:
The qualitative negative respirator fit check requires you to exhale gently to test the seal. During gentle exhalation, the muscles relax and surface tension in the alveoli creates a positive pressure inside the lungs, forcing air out. Pressure between the chest wall and lungs remains negative to keep them attached to the chest wall, but it is less negative than during inhalation.