Which statement correctly describes cabin O2 flow on the 787?

Which statement correctly describes cabin O2 flow on the 787?

• A. It Flows Continuously At All Times
• B. On Demand And Delivers Small Puffs Only When The User Inhales
• C. Only Flows When The Mask Is Donned
• D. Inactive During Cabin Altitude Changes

Answer: (B)

Cabin oxygen on the 787 is demand-based. Each passenger mask delivers oxygen only when you inhale, through a sensor that opens a small valve and releases a puff with each breath. This on-demand flow means oxygen isn’t wasted as a continuous stream; you get oxygen precisely when you take a breath. The masks deploy automatically at cabin altitude, but the actual oxygen flow starts only with inhalation, not just because the mask is in place. The other ideas—continuous flow at all times, flow only when the mask is donned, or being inactive during altitude changes—don’t match how the 787’s system conserves oxygen and provides it in response to breathing.

Cabin oxygen on the 787 is demand-based. Each passenger mask delivers oxygen only when you inhale, through a sensor that opens a small valve and releases a puff with each breath. This on-demand flow means oxygen isn’t wasted as a continuous stream; you get oxygen precisely when you take a breath. The masks deploy automatically at cabin altitude, but the actual oxygen flow starts only with inhalation, not just because the mask is in place. The other ideas—continuous flow at all times, flow only when the mask is donned, or being inactive during altitude changes—don’t match how the 787’s system conserves oxygen and provides it in response to breathing.