What initiates the air flow to the receiving cylinder in the RIC UAC?

The correct answer is that both cylinders equalizing initiates the air flow to the receiving cylinder in the Rapid Intervention Crew (RIC) UAC. This equalization process is essential for determining the appropriate flow of air from the donor cylinder to the receiving cylinder.

When the air pressure in both cylinders is equalized, the valve system is designed to open and allow air transfer. This ensures that air can flow from the higher-pressure cylinder (donor) to the lower-pressure cylinder (receiver) until balances in pressure are achieved. This mechanism is crucial in emergency situations, as it allows for a safe and efficient transfer of air while ensuring that the receiving cylinder maintains a sufficient supply during critical operations.

Manual interventions or valve activations, while necessary for controlling the system, are secondary to this pressure equalization process, which specifically triggers the air flow. The other options relate to other functions within the SCBA system but do not directly initiate the air flow to the receiving cylinder.