In certain circumstances, a mobile/portable surface-supplied system, commonly referred to as SCUBA-replacement equipment, can be used instead of a complete surface-supplied diving system. The portable nature of such systems offers greater flexibility but this is offset by the limited supply of breathing air that is available.

This guidance sets out what is regarded as good safe practice by the diving industry when using this type of equipment. In general it is expected that this technique will be used when diving from a small craft with a fully equipped diving support vessel in the vicinity. The diving operation should be planned so that decompression is not required.

It is not intended that this equipment should be used as a substitute for a complete surface-supplied diving system if a full system can be accommodated at the dive site.

In particular the guidance contains information on: risk assessment, equipment requirements, depth limitations, minimum gas requirements, medical equipment, decompression chamber facilities, umbilicals, etc.