Frequently drownings occur in spite of apparently adequate patrolling of beaches and lakes by trained lifeguards. A swimmer who, because of panic or exhaustion, sinks beneath the surface of the water is usually quickly lost to sight. The task of the lifeguard is to swim down under water, holding his breath, in an attempt to locate the drowning person. Holding the breath while undergoing the exertion of swimming under water is extremely tiring. Rarely can an untrained person remain under water in this manner for more than one minute or dive deeper than about 30 feet. When the lifeguard does come to the surface for air he is exhausted, and his successive dives will necessarily be shorter and shallower until finally he can no longer continue. Valuable time is wasted in coming to the surface for air, and time is an all-important factor in an emergency of this sort.
Lambertsen CJ. A DIVING APPARATUS FOR LIFE SAVING WORK. JAMA. 1941;116(13):1387-1389. doi:10.1001/jama.1941.62820130001015