How should a Dive Supervisor respond to a primary gas supply failure during a dive?

• A. Ignore and continue to the target depth.
• B. Switch to standby bailout gas, implement emergency ascent/return, and notify open-water rescue plan.
• C. Wait for surface team to fix gas while divers remain underwater.
• D. Attempt to substitute with an alternative gas without procedure.

Answer: (B)

When breathing gas is lost underwater, the priority is to preserve life by ensuring a valid source of breathing gas and a safe path to the surface. The appropriate response is to switch immediately to the standby bailout gas so the divers have a known, controllable supply, then carry out an emergency ascent or return to the surface while coordinating with surface support. This sequence minimizes the risk of hypoxia or being left without gas, and it keeps the ascent controlled with time and depth managed according to the dive plan. At the same time, you must notify and activate the open-water rescue plan so surface personnel can assist, monitor, and prepare for a possible surface rescue.

This approach is preferred because it uses preplanned contingency gas, maintains breathing competency, and provides a clear, organized path to safety. Ignoring the issue, waiting for surface repairs while underwater, or substituting gas without a formal procedure could lead to uncontrolled ascent, incorrect gas mixtures, or a catastrophic gas failure at depth.