Page 73 - International safety guide for oil tankers and terminals
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HAZARDS OF PETROLEUM





      ---ใช้เพื่อการศึกษาเท่านั้น---



               งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
                                                                                             Wind





                                                                                 approx
                                                                                 15 m












                                                      approx 8 m




                                                                                 Deck ึ






                                 c) Total gas flow 46 cubic metres/minute. Approximate loading rate 2300 tonnes/hour.
                                 The above illustration shows a vent riser 6 metres above the deck.

                                 The plumes are based upon wind tunnel data of:
                                        Gas mixture  50% by volume propane in the air
                                 Diameter of opening  254 millimetres
                                        Wind speed  1.1 metres/second



                                    Figure 2.3 (c) – Indicative effect of gas flow rate on flammable zone



                                        The flammable zones generated by the same operations with motor or
                                        aviation gasolines would be similar but with a more pronounced density
                                        effect, and this effect would be even more pronounced with a natural
                                        gasoline type cargo. Also, the greater dilution required to reach the LFL
                                        with motor or aviation gasolines (see Section 1.2.2) would tend to make
                                        the flammable zones larger than with crude oils, and this effect would be
                                        even more pronounced with the natural gasolines. Thus, the dispersion
                                        problem becomes progressively more pronounced as one goes from
                                        crude oils, through motor or aviation gasolines, to natural gasoline type
                                        cargoes.

                              2.5.4.4 Concentration of Hydrocarbon Gas

                                        With a constant total rate of flow of gas, changes in hydrocarbon
                                        concentration have two effects. The rate of emission of hydrocarbon gas
                                        increases in proportion to the concentration so that, other things being
                                        equal, the extent of the flammable zone increases. Also, the initial density




                                                   © ICS/OCIMF/IAPH 2006                                        39
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