This from Magnus Råström @ Black Diamond Equipment AG
"There was a ice climbing accident last season, no one got hurt but it could have ended really bad and the ice climbers were using our (BD) Express screws. Christ Semmel working for DAV investigated the accident and attached is his report in German. I have below a short summary in English.
Course of Action:
2 Ice climbers doing a multipitch route in Austria, using Mammut double ropes, for protection BD Express Ice Screw with a Austria Alpin QD Easy Classic and for belay a reverso. The axe and crampons of the lead climber (belayed from below) did pull out and the climber fell 12 m without ice contact or injury, but the mantel ripped on one of the ropes (see photo page one, blue rope). Chris came to the conclusion that the rope ripped because it was pulled over the crank knob of the ice screw. The photo on page one, red rope is the rope which they have tested and pulled over a crank knob. Chris is not negative against our ice screw’s and the conclusion is that when ice climbing with ice screw’s with crank knobs it is important to fold them in after use. Also he recommends the use of ice screws with crank knobs that you can fold in.
All the best,
Magnus Råström / Black Diamond Equipment AG"
I use and like both the BD Express and Grivel Helix.
I do how ever use Grivel Helix in much of my own steep water ice climbing with an obvious crank knob that does not fold in. Worth noting the BD knobs are sharp in comparison. It should be pretty obvious you don't want a rope running over them that will take weight. The BD knob diameter at the small end is 9.5mm and the Grivel 15.5mm. The Grivel knob is a synthetic, likely Delrin and smooth. BD's knob is knurled aluminum and likely the last thing any of us want to run a rope over. I don't want my rope running over either in a fall. But if given a choice...I'll take a folded knob over the Grivel option.
But that isn't the total story. You need to know more.
The direction at which you clip the hangers should also be very different on the BD as opposed to the Grivel screws. The Grivel hanger offers a bit more play to set a screw and have the hanger flex on the screw to clear the ice. That allows the Grivel knob to be closer to the ice where the BD hanger will always be forced intentionally to the outside. Flip the BD knob down and you won't have a problem there. Not so on the Grivel as you have no option but to hide the know in the terrain. .
I disagree some what with Magnus' synopsis of the report and if that was accurate (and no reason to think it was not) the DAV report itself.
Here is why:
It you hang a rope on the Grivel hanger it is more likely to do one of two things in my opinon :
One: It will slide off to the outside of the hanger on the slick Delrin material
Two: Or depending on the hanger clearance from the ice get trapped behind the hanger and run on the 16.5mm screw body itself and or the horizontally positioned hanger body.
Either option I would prefer to knurled aluminum and a vertical positioned 2.5mm thick stainless hanger. So close your knobs on the BD Express screws! And I wouldn't use screws with a fixed small diameter (knurled or not) knob that mimics BD's hanger design is what I take away from this. It is splitting hairs but important hairs I think.
It is all about the details, be careful out there!
Beal 7.8 Ice twin on the BD knob which when left open caused a sheath failure in the fall.
I have no doubt you could catch a rope on the Grivel hanger, which you really do not want to do. Bottom line is be careful out there and think about each and every placement. For my money twin or dbl ropes on ice make a lot of sense.
Two pictures of the Grivel Helix in the position a rope would normally be caught from above. With the hanger totally at the end of its movement and the carabiner hole is to the inside, the knob is angled down so a rope would generally just slip off of it or the rope will run behind the hanger and on to the screw tube body. This seems an unlikely event (but certainly possible) because only ice behind the knob end of the hanger would force it into this position.
If the hanger does have space behind it after the screw is placed no question you can easily hook the rope there in a fall.
But again better a 17.5mm radius (Grivel's tube) to run your rope over than a 9.5mm radius (BD's knob) with the addition of several sharp edges to help the damage along.
Worth repeating I think.
For my money twin or dbl ropes on ice make a lot of sense.
Miles of vertical ice have been climbed with either style screw and hanger and as many miles with screws and hangers not nearly as good. I'll continue to climb on both BD and Grivel screws and choose accordingly to which fits my project best. I'm not suggesting panic here just that you keep your eyes and mind open to the possibilities.