BFK rolling under high shelf-only load ?

Is there a concern with BFK anchors that, if a user clipped to the shelf manages to generate a high load and the master point is empty, the BFK knot could roll and result in either (a) huge extension (odd number of anchor points) or (b) complete loss of attachment (even number of anchor points + bad luck) ?  Or is the scenario too far-fetched to be of concern ?

On https://americanalpineclub.org/resources-blog/2016/6/27/the-masterpoint-the-shelf-the-components-anchor-anatomy-in-action the photos show a (seemingly useless) carabiner on the master point whenever a BFK shelf is used. But I haven't (yet) seen an explicit rule requiring the master carabiner to remain in place during shelf use for BFK anchors..

(this topic is about BFK anchors - girth/clove hitch master points are a different story)

Rolling AKA capsizing of a Fig 8 knot (or more rarely, an overhand) requires that the ropes entering the knot be pulled WIDELY apart. Think rap ropes joined this way. The load on the shelf doesn't generate this force vector.

Sorry nevermind - I found it (https://www.climbing.com/skills/learn-this-using-the-anchor-shelf/): "Note: For this system to be solid, you must have a biner clipped through the master point—weighted or unweighted—so there’s no way the knot can come undone"

(but I do think rolling would require an unusual event like a FF2 leader fall or FF1 PAS fall)

Serge S wrote:

Is there a concern with BFK anchors that, if a user clipped to the shelf manages to generate a high load and the master point is empty, the BFK knot could roll and result in either (a) huge extension (odd number of anchor points) or (b) complete loss of attachment (even number of anchor points + bad luck) ?  Or is the scenario too far-fetched to be of concern ?

I've never heard of a failure with the situation you describe, but you can ease your concerns in two ways:

1. If you roll the knot back through the initial bight loop, the loop would have to pull through the extended anchor arms. Always roll the knot through the loop to finish the knot.

2. You can also clip a carabiner through the loop and to one of the anchor arms.

Serge S wrote:

Sorry nevermind - I found it (https://www.climbing.com/skills/learn-this-using-the-anchor-shelf/): "Note: For this system to be solid, you must have a biner clipped through the master point—weighted or unweighted—so there’s no way the knot can come undone"

(but I do think rolling would require an unusual event like a FF2 leader fall or FF1 PAS fall)

Well, Hell.

I was responding, but got caught on a phone call. When I finally post I see you got your answer. 

Climb on, Serge. Be safe.