CT test procedures

Just curious what others use for their technique for the compression test. I have always referred to the NWAC rough correlations for the CT procedure of 5 sets of 6 blows to the shovel. But I have been hearing more from other about 3 sets of 10 blows .

in the end, it may be comparing apples to oranges, but it seems like 3 sets of 10 is easier to remember and explain to others.

I am curious of community feedback, what do you use, why?

I pay more attention to shear quality than tap strategy.

Avalanches are caused by delamination, and while I am somewhat interested in how much force is required, I am much more interested in whether or not the snowpack is prone to delamination in the first place. This is because once fracture toughness is exceeded, it doesn't matter by how much. In addition, there is less variability with respect to shear quality.

My blog has an exhausting rant if you're interested.

avalanchesafety.blogspot.com/2009/12/sno...ons-maintaining.html

p.s. This is my own preference. It is not necessarily safe to adopt my methods. Your mileage may vary. These methods may not be safe for less experienced observers.

I pay more attention to shear quality than tap strategy.

Avalanches are caused by delamination, and while I am somewhat interested in how much force is required, I am much more interested in whether or not the snowpack is prone to delamination in the first place. This is because once fracture toughness is exceeded, it doesn't matter by how much. In addition, there is less variability with respect to shear quality.

My blog has an exhausting rant if you're interested.

avalanchesafety.blogspot.com/2009/12/sno...ons-maintaining.html

p.s. This is my own preference. It is not necessarily safe to adopt my methods. Your mileage may vary. These methods may not be safe for less experienced observers.

The point of CT and ECT tests are help collect data for your educated guess on whether or not you think skiing will exceed the fracture toughness as you call it. Nearly all non summer snowpacks will fracture if you put enough force on them. Both the force needed and the quality of the fracture are important to know.

To the OP, I was taught 3x10 taps in Avy 1 and it seems to work just fine.

The point of CT and ECT tests are help collect data for your educated guess on whether or not you think skiing will exceed the fracture toughness as you call it. Nearly all non summer snowpacks will fracture if you put enough force on them. Both the force needed and the quality of the fracture are important to know.

I am well-aware of the purpose of snowpack tests.

Nearly all non summer snowpacks will fracture if you put enough force on them.

Which is why I'm more interested in shear quality than fracture toughness. The number of taps really constitutes a rough index of instability ( Class II ) rather than a sign of instability ( Class I ). Q1 and Q2 always get my attention, and regardless of the number of taps, I interpret both as signs of instability. I am comfortable assuming that skiing applies at least as much force as taps from the shoulder.

( The term fracture toughness comes from material science, and is used throughout The Avalanche Handbook. )

thanks guys, you both have good information on the mechanics of the CT test. regarding the two procedures in my OP I was looking for something like if the 5x6 provides better resolution than the 3x10.

I'm leaning towards using the 3x10 method in the field, but then I will need to read up on this more.

When reading reports, I tend to assume that a failure at CT21 is the first tap from the shoulder - thanks for the enlightenment that there are other protocols in use out there. .

I could believe that 5x6 might give better resolution, but may be somewhat less "standard".