4 Prevention of Dust Explosion
4.0.1 For petrochemical particulate solids with different nature，corresponding measures shall be taken based on their minimum ignition energy.When minimum ignition energy of particulate solids（MIE）is greater than 30mJ，propagating brush discharge and insulated conductor spark discharge（including human body discharge）shall be prevented，and when the particulate solids of the minimum ignition energy（MIE）is less than or equal to 30mJ，measures shall be taken to eliminate particulate solids electrostatic and to inhibit the accumulation of combustible gas in addition to the foregoing two types of discharge.The minimum ignition energy value of typical petrochemical particulate solids products may be gotten from Appendix B of this Code.
4.0.2 Measures shall be taken to reduce the generation and accumulation of dust when handling petrochemical particulate solids.
4.0.3 For meeting the product quality requirements，measures shall be taken to prevent petrochemical particulate solids from pelletizing destabilization and forming"streamers".
4.0.4 When volatile content in material is high，or combustible gas content in silo is higher than the 20% of gas lower explosive limit（LEL），purging gas system shall be provided.
4.0.5 When blowback purging gas at bottom is adopted in design，the minimum flow alarm shall be provided.
4.0.6 The purging gas flow rate of particulate solids silo shall be determined based on escape rate of the particulate solids volatiles and minimum ignition energy of the dust.The minimum flow rate of purging gas shall ensure that the minimum ignition energy of hybrid mixture is not less than 12mJ.When the volatiles escape rate data is unavailable，the purging gas flow rate may be estimated according to the requirement that gas concentration in silo is less than 20% of the gas lower explosive limit（LEL）.
4.0.7 The minimum ignition energy of hybrid mixture may be calculated by the following equation:
where:
MIEH—the minimum ignition energy of hybrid mixture（mJ）；
MIED—the minimum ignition energy of dust，（mJ），it may be gotten from Appendix B of this Code；
MIEG—the minimum ignition energy of combustible gas，（mJ），it may be gotten from Appendix C of this Code；
CP—sensitive concentration of ignition of combustible gas，（%），it may be gotten from Appendix C of this Code；
C—combustible gas concentration（%）.
4.0.8 Particulate solids silos shall be designed to reduce the content of dust in silo gas phase space，the purging gas pressure and flow rate should be appropriate.
4.0.9 The purging gas system shall be designed to be free from clogging and to be convenient for inspection and maintenance.The elevation of the intake filter of the purging gas blower should not be less than 1.5m from grade，and shall be equipped with rain shelter or rain cover.For silos that are prone to electrostatic explosion，loading of silo and purging gas blower shall be of automatic interlock design.
4.0.10 Air intake of purging gas blower shall be located in a non-explosive area，if there is any combustible gas release source or combustible gas leakage risk in the local area，combustible gas detector shall be located.
4.0.11 For meeting the product quality requirements，the content of components with high boiling point in the reactants shall be reduced.
4.0.12 For silos with high concentration combustible gas，their vent ports should be equipped with combustible gas detection and alarm system.
4.0.13 Off-spec product in off-spec silo or intermediate silo shall be purified to be qualified and then returned to the normal process system.
4.0.14 When off-spec silos are more than one，each silo should be equipped with independent purging gas system otherwise automatic control measures shall be taken for valves on purging gas piping and feed piping for each silo.
4.0.15 Particulate solids specified in Articles 4.0.13 and 4.0.14 of this Code shall be handled continuously.For intermittent handling of materials（including sampling，testing，etc.），it shall maintain necessary purging gas by control system，and new feeding of silo may be introduced after previous material is emptied.
4.0.16 Good ventilation environment shall be kept at the discharging and packaging ports.
4.0.17 When the piping gets blocked，purging and unblocking gas must not contain any combustible component，and compressed air must not be used to purge tank and container containing combustible gases and dust.