What defines an adequate emergency gas supply (EGS) for divers?

The definition of an adequate emergency gas supply (EGS) for divers is based on the need to ensure diver safety during ascent. An emergency gas supply must provide sufficient air not only to reach the surface but also to allow for safe decompression stops if necessary. This means that for dives that could result in decompression sickness, having enough gas to reach the first decompression stop is crucial.

Option B accurately captures this need by stating that the EGS should provide sufficient air to reach either the first decompression stop or the surface for No-D dives, where decompression stops are not required. This guideline ensures that divers have enough gas in case of emergencies, emphasizing the importance of planning for potential problems during a dive.

Other options do not cover the full scope needed for safe diving practices. For instance, while supplying gas to reach the surface may seem sufficient, it fails to account for the critical decompression stops necessary for deeper dives to prevent decompression illness.