If cockpit pressure differential exceeds 4.0 psi, what does the safety valve do?

When the cockpit pressure differential exceeds 4.0 psi, the safety valve opens to relieve the excess cockpit pressure. This is a critical function of the safety valve because it protects the structure of the aircraft and the safety of its occupants by preventing over-pressurization.

The operation of the safety valve ensures that the pressure in the cockpit remains within safe limits, preventing potential structural damage to the aircraft that may occur if the pressure were to continue rising unchecked. Additionally, by relieving excess pressure, it enhances the safety and comfort of the flight crew and passengers. Thus, option B correctly describes the action taken by the safety valve in response to high cockpit pressure differential.