Hyperbaric evacuation and rescue is the emergency hyperbaric transportation of divers under a major decompression obligation to a place of safety where decompression can be completed at acceptable risk and in reasonable comfort.[1]
Divers in saturation inside a diving system cannot be quickly decompressed to be evacuated in the same way as other installation personnel. The divers must be transferred to a pressurised chamber which can be detached from the installation's saturation diving system and transported to a safe location. A hyperbaric evacuation unit (HEU), also known as a hyperbaric rescue unit (HRU), with the capacity to evacuate the maximum number of divers that the diving system can accommodate, is required, with a life support system that can maintain the hyperbaric environment for at least 72 hours. After the initial evacuation, the HEU and its occupants are taken to a designated location where they can be safely decompressed to surface pressure.[2]
The preferred way is to provide a self-propelled hyperbaric lifeboat (SPHL). Hyperbaric rescue chambers without propulsion (HRCs) are also accepted, but requirements for life support and recovery are complicated by limitations of design and configuration, and the unit must be towed clear of the evacuated installation by another vessel. Detailed guidance on hyperbaric evacuation is provided in IMCA D 052 - Guidance on hyperbaric evacuation systems.[2]
After launching, the HEU is recovered by the standby hyperbaric rescue vessel (HRV) and transported to the standby hyperbaric reception facility (HRF), where the divers are transferred under pressure and decompressed in relative safety and comfort. In remote locations the HRF may be mounted onboard the HRV.[3]
Another type of hyperbaric evacuation is for medical purposes, usually for a single diver, and may be done in a portable chamber for one or two occupants or a hyperbaric stretcher, The diver may be in saturation or being treated for decompression illness, so the pressure will be either the saturation pressure or treatment pressure, which is usually much lower, at about 18 msw (2.8 bar absolute), with the diver on an oxygen treatment table. The second occupant is usually a hyperbaric chamber attendant, to provide any necessary emergency medical assistance. Portable chambers may be transported by any vessel of opportunity, road transport vehicle or helicopter capable of carrying the load.[4]
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