Divers are vulnerable to suction or turbulence caused by water intakes and discharges. The diving contractor will need to establish with the client whether there are any underwater obstructions or hazards in the vicinity of the proposed diving project. If there are any intakes or discharges, suitable measures will need to be taken to ensure that these cannot operate while divers are in the water unless the divers are adequately protected by a suitable physical barrier. Such measures will need to be part of a work control system, such as a permit-to-work system, and could include mechanical isolation.

Underwater approaches to operating intakes, exhausts, and water-control structures shall be declared hazardous locations for diving operations. Operating intakes and exhausts include those units which do not currently function, but which are capable of being operated at any time.

Divers diving in these environments shall only use surface-supplied equipment with voice communications and be tended from a position outside the hazardous area at all times.

When practicable the free length of the umbilical should be restricted to prevent the diver from entering the hazard zone.

When a diver is required to approach any underwater intake pipe, tunnel, or duct, he/she shall be provided with means to identify the intake in such a manner as to distinguish it from any other similar intake in the location.

The diver shall not approach any intake until the flow through it is stopped or controlled. Provisions shall be made so that the flow cannot be re-established until the diver leaves the water or until the diving supervisor has declared the diver clear of the location.

When the flow cannot be stopped, the safety of a diver approaching the intake shall be assessed by the determination of flow patterns using direct measurement, calculation, or other means acceptable to the diving supervisor.