Why must ascent rates be controlled?

• A. To conserve air
• B. To prevent bubble formation in tissues
• C. To reduce heat loss
• D. To prevent noise

Answer: (D)

As you ascend, the surrounding pressure drops, and dissolved nitrogen in your tissues must off-gas gradually. If you rise too quickly, nitrogen can come out of solution too fast and form bubbles in tissues and in the bloodstream. Those bubbles can block vessels or damage tissues, leading to decompression sickness and other serious injuries. Controlling ascent rate gives the body time to off-gas safely, reducing the chance of bubble formation. Safety stops further aid this off-gassing by providing additional time at a shallow depth. This is the main reason for limiting ascent speed; conserving air, reducing heat loss, or preventing noise aren’t the primary safety concerns in this context.