Complex sentence: The surface supplied equipment evolved into lightweight demand helmets, which are more economical with breathing gas, and saturation diving reduced the risks of decompression sickness for deep and long exposures, while an alternative approach was the development of the "single atmosphere" or armoured suit.
Split into simpler sentences: The surface supplied equipment evolved into lightweight demand helmets, which are more economical with breathing gas, and saturation diving reduced the risks of decompression sickness for deep and long exposures. An alternative approach was the development of the "single atmosphere" or armoured suit.