The provisions of this section of Part 2 in the 2002 BSS Standards are mandatory for non-private boats where applicable.
Pollution can be caused by fuel coming out of the vent terminal when the fuel tank is overfilled. To minimise waterway pollution the vent pipe outlet must be at a height that is equal to, or greater than, the height of the deck filling connections. It's recommended that the position of the vent pipe outlet is at least 100mm (4ins) above the filling point.
The outlet of the vent pipe can be below the level of the deck filling connection, as long as there's a swan neck in the line that extends the pipe to a point just beneath the filling connection.
As the vent pipe will be regularly 'breathing' fuel vapour, the outlet must be positioned away from potential sources of ignition.
Any flame close to or at the end of the vent pipe could flash back into the fuel tank. Because of this, each vent pipe opening must be fitted with an effective flame arrester (see diagram - outlet of vent pipe below deck level) that prevents flashback. It's recommended that the flame arrester has gauze with mesh not less than 11 to the linear centimetre (or 28 to the linear inch) and to be effective the gauze must also completely cover the pipe opening. You can help maintain its effectiveness by keeping it clear of debris such as paint or spiders' webs. [2.5]