Flare header sweep gas

[Ash-]

Hello Guys,
Is there any requirement/recommendation (preferably a reference to a standard like API 521 or a code) about the sweeping/purging gas for the flare header?
I see it is common that the essential purging gas is applied at the end of the flare header. My question is that what happens if we apply the purging gas at the base of the flare stack (to a mount exceeding flame velocity by a margin—to prevent fire flashback) and not at the end of the flare header?
Thanks

 

[Snickster]

Here is part of an old Mobil design guide for relief systems which provides recommended purging and flashback protection.

 

[shvet]

My question is that what happens if we apply the purging gas at the base of the flare stack (to a mount exceeding flame velocity by a margin—to prevent fire flashback) and not at the end of the flare header?

Nothing if the header is maintained at positive pressure. See attached the video of the opposite.

Also attached a couple of relevant outdated users' practices

 

[Ash-]

Nothing if the header is maintained at positive pressure. See attached the video of the opposite.

Also attached a couple of relevant outdated users' practices

Thanks the txt file was gold