What should divers breathe during temporary O2 loss in the chamber during Sur 'D'?

During a temporary oxygen loss in the chamber during saturation diving operations, divers should breathe chamber air. This is primarily because chamber air, which is typically a mix of oxygen and nitrogen, provides a safe and immediate source of breathable gas. In the event of a loss of oxygen, the chamber air ensures that divers maintain their required levels of oxygen while also preventing a rapid increase in carbon dioxide levels, which could occur if the divers were restricted to only pure oxygen.

Chamber air is specifically designed to be safe for respiratory use at the pressures encountered during saturation diving. It maintains normal physiological function for the divers as they remain under pressure, avoiding complications that might arise from breathing gases that are not suitable or could cause toxic effects, such as a high concentration of pure oxygen.

Utilizing a 50/50 gas mix or other non-standard breathing gases, like an air mix with contaminants, can introduce additional risks, such as toxicity or the creation of a hypoxic environment, which are not present when using chamber air. This makes chamber air the most appropriate and safe choice during such emergencies.