SEM-SAFE® low-pressure CO₂ fire safety system The SEM-SAFE® low-pressure CO₂ systems are intended for use where large machinery and cargo spaces require protection with carbon dioxide. The advantage of the low-pressure system is that one single tank replaces a large number highpressure CO₂ cylinders with an approximate saving of 50% in weight. The tank, main valves, distribution valves, refrigerators, cooling unit and associated controls are supplied prewired and ready assembled on a common steel frame. The quantity of carbon dioxide is shown directly by an electronic gauge indicating the actual tons of CO₂ in the tank. The gauge unit is fitted with alarm contacts for warning of low CO₂ contents in the tank. Recharging after use is done directly from a truck. For large vessels the installation cost of a low-pressure CO₂ system is considerably lower compared to the installation costs of a high-pressure CO₂ system. The system is designed to meet the requirements of the appropriate classification societies to which the vessel is being built. Tank The tank is constructed as a steel pressure vessel in accordance with the classification society requirements. The tank is equipped with two safety valves, which are fitted to a three way changeover valve, thus one safety valve is connected to the vessel if the other one is out of operation. The tank unit is supplied complete and ready for use, installed on a rectangular steel framework and held in position by thermally insulated supports. The tank is insulated with non-flammable polyurethane foam protected by an aluminium cover. Cooling units The cooling units are installed at the end of the tank on the support frame and are completely duplicated both mechanically and electrically. The refrigerant is environmentally friendly and the cooling circuits on the compressors and condensers are suitable for either seawater, fresh water or air-cooling. CO₂ is maintained at a temperature of –18°C, which is equivalent to a CO₂ storage pressure of 2.1 MPa. CO₂ level indication An electrical capacitance type liquid gauge is fitted and the meter is calibrated. The indicator has an accuracy of +/- 2% and is fitted with an alarm switch indicating minimum filling level. Benefits There are many benefits of the SEM-SAFE® low-pressure CO₂ system for fire safety compared to high-pressure CO₂ cylinders: • Compact system with low complexity: one ready assembled and tested low-pressure CO₂ unit instead of hundreds of high-pressure CO₂ cylinders. • “Plug & Play” installation. • Low-maintenance cost: checking the content annually is done quickly and easy with low-pressure CO₂ unit as only one instrument needs to be read; high-pressure CO₂ requires time-consuming weighing of every cylinder and for many level indicators to be inspected. • Lower system weight. • Less space required: only 60m2 for SEM-SAFE® low-pressure CO₂ unit compared to 150-300m2 for high-pressure CO₂ cylinders. • Easy installation and savings: between 100 and 200 man hours are required for the installation of the low-pressure CO₂ unit; installing high-pressure CO₂ cylinder can take between 400 and 1000 man hours. • Fast re-filling after release: 12 man hours are needed for refilling a low-pressure CO₂ unit compared to 2,500 man hours required for high-pressure CO₂ cylinders. • No need for pressure test after ten years. 2 Danfoss Fire Safety A/S · SEM-SAFE®low-pressure CO₂ fire safety system
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