Vent to atmosphere (gooseneck)

ISO 10628-2 (groups 24-25, fittings and piping) / PIP PIC001

Drawn as

A line rising and turning back down at the top (a gooseneck or bent open end), sometimes with "ATM" written beside it.

Meaning

Open vent to a safe location: instrument-air and nitrogen relief, tank vents and utility PSV outlets. For hydrocarbons, cold vents go to a vent stack instead.

Variants

A plain open end with "TO ATM"
A mesh or bird screen may be drawn at the end