Ground flare with flames

This is the ground flare of the Olefin Unit 4 at BP's RuhrOel GmbH refinery.

You see a huge fire at one of it's ten 'windows'.

The ground flare is part of the safety device of an ethylen plant
This steamcracker crack naphtha and liquid gas under addition of steam in big furnaces
(at a temperature of approx. 815°C) to make ethylen, propylen, butadien, pygas, benzene, fuel gas etc.

Ethylen is a primary product to produce plastics etc.

At normal operation, small volume of gas burns into this ground flare.
To start up the plant, gas must sent to the flare until the specification is ok!
With a sudden failure (for example power outage) the gas went to the big flare, 60 meters north of the ground flare.