content of the chamber gas is constantly monitored and fresh oxygen added when necessary to maintain the nominal value. chamber gas may be simply vented and flushed if it is air, but helium mixtures are expensive and over long periods very large volumes would be needed, so the chamber gas of a saturation system is recycled by passing it through a carbon dioxide scrubber and other filters to remove odours and excess moisture. multiplace chambers that may be used for treatment usually contain a built-in breathing system (bibs) for supply of breathing gas different from the pressurisation gas, and closed bells contain an analogous system to supply gas to the divers' umbilicals. chambers with bibs will generally have an oxygen monitor. bibs are also used as an emergency breathing gas supply if the chamber gas is contaminated. sanitation systems for washing and waste removal are required. discharge is simple because of the pressure gradient, but must be controlled to avoid undesired chamber pressure loss or fluctuations. catering is generally provided by preparing the food and drink outside and transferring it into the chamber through the stores lock, which is also used to transfer used utensils, laundry and other supplies. non-portable chambers are generally constructed from steel, as it is inexpensive, strong and fire resistant. portable chambers have been constructed from steel, aluminium alloy, and fibre reinforced composites. in some cases the composite material structure is flexible when depressurised. operation diving barocomplex savior of the pacific fleet of russia details will vary depending on the application. a generalised sequence for a stand-alone chamber is described. the operator of a commercial diving decompression chamber is generally called a chamber operator, and the operator of a saturation system is called a life support technician (lst). pre-use checks will be conducted on the system to ensure that it is safe to operate. the intended occupants will be checked and authorised for compression, and will enter the chamber. the pressure door will be closed, communications established with the occupants, and pressurisation started. the operator will monitor and control the rate of pressurisation and monitor the condition of the occupants. once pressurised, the operator will monitor the pressure, the run time, the chamber gas and if applicable, the independent breathing gas supply. the chamber gas quality may be controlled by carbon dioxide scrubber systems, filters and air conditioner systems and addition of oxygen as required, or by periodic ventilation by adding fresh compressed air while simultaneously releasing some of the chamber air. when decompression is started, the operator will notify the occupants and release chamber gas to the atmosphere or to scavenge pumps if it to be recycled. the rate of pressure reduction is controlled to follow the specified decompression schedule within tolerance. compression and decompression may be interrupted if the occupants experience problems caused by the pressure change, such as ear or sinus squeezes, or symptoms of decompression illness. when decompression is completed, chamber pressure is equalised with ambient pressure and the doors may be opened. occupants may exit, and will usually be checked for absence of ill-effects. chamber will receive post-operation service as required to be ready for next operation or storage as applicable. working pressure a large range of working pressures are used, depending on the application of the chamber. hyperbaric oxygen therapy is usually done at pressures not exceeding 18msw, or an absolute internal pressure of 2.8 bar. decompression chambers are usually rated for depths similar to the depths that the divers will encounter during planned operations. chambers using air as the chamber atmosphere are frequently rated to depths in the range of 50 to 90 msw, and chambers, closed bells and other components of saturation systems must be rated for at least the planned operational depth. the us navy has heliox saturation decompression schedules for depths up to 480 msw (1600 fsw). experimental chambers may be rated for deeper depths. an experimental dive has been done to 701 msw (2300 fsw), so at least one chamber has been rated to at least this depth.