4.3　Emission Facilities of Outdoor Units

4.3.1　For the emission facilities（such as dispersing pipe，exhaust duct，safety valve，breathing valve，discharge port，sampling port and blowdown port）installed on the top and upper outer position of process equipment that are vulnerable to direct lightning flash and directly venting into atmosphere，specific design against lightning shall be made for them based on emission characteristics such as emitted substances and their concentrations，emission frequency or modes，normal or emergency emission，manual or automatic emission，as well as their installation positions.

4.3.2　Air terminal shall be provided against lightning for any one of the following vents.In this case，explosive gas space beyond the vent shall be located within the protection zone afforded by air terminal，the tip of air terminal shall be 3m higher than the vent，and the horizontal distance should be 4m-5m.

1　Vent that is provided on equipment used to store flammable liquid with flash point lower than or equal to 45℃，and its continuous emission is up to explosion hazardous concentration during emergency shutdown（including temporary vent in the pipes of flare system，but excluding flare）；

2　Vent that is provided on thank used to store flammable liquid with flash point lower than or equal to 45℃and its breathing valve is not provided with flame arrestor.

4.3.3　Metal vent nozzle should be served as air terminal for any one of the following vents.In this case，the wall thickness of vent pipe nozzle shall be larger than or equal to the thickness value，t′，indicated in Table 6.1.5 of this Code，and metal bonding shall be made for the vent pipe from a location near to the pipe nozzle to the nearest metal object.

1　Vent that is provided on equipment used to store flammable liquid with flash point lower than or equal to 45℃，and its continuous emission during normal operation may reach explosion hazardous concentration in short period or intermittently.

2　Safety valve that is installed on equipment used to store flammable liquid with flash point lower than or equal to 45℃，and its manual or automatic emission in short period due to overpressure inside equipment during process upset may reach explosion hazardous concentration.

3　Discharge port that is installed on equipment used to store flammable liquid with flash point lower than or equal to 45℃，and it is required for manual venting during shutdown or maintenance.

4　Breathing valve that is provided with flame arrestor and installed on equipment used to store flammable liquid with flash point lower than or equal to 45℃.

5　Vent stack and flare that are individually installed in open fields.