Where, How High, How Much? A New Calculator for Avalanche Control Blasters
Every avalanche blaster knows that the same charge does not do the same job twice. A hand charge that clears one start zone can leave the next one hanging. The reasons are well known in the field: where the charge sits, how steep the slope is, what the snow is like, and how high the site is. What has been missing is a simple way to put numbers on those differences.
Three panels underneath:
- Trigger criteria (SLF): stable snowpack 2.0 kPa (0.29 psi), reached to 43 m (140 ft); intermediate 1.0 kPa (0.145 psi), to 70 m (230 ft); unstable snowpack 0.25 kPa (0.036 psi), to 188 m (616 ft).
- Charge location: range to the 1 kPa criterion for the same 1 kg charge is 70 m elevated, 49 m on the snow and 8 m buried. It also shows the uphill and downhill pressures and the effect of site elevation.
- Snow type: dry wind slab gets the full range; very stable hard slab and wet snow are limited to under 10 m (33 ft); a persistent weak layer can release far from the charge.
Petr Explosives Group has built the PETS Avalanche Blast Calculator to do that. It is an Excel tool for training and shot planning, based on the same air-blast curves used in ConWep and on published research from the Swiss Institute for Snow and Avalanche Research (SLF).
What it shows
- Placement. A charge raised on a pole reaches much farther than the same charge thrown on the snow, and a charge that sinks in loses most of its effect. In our example, a 1 kg charge has a planning range of about 70 m when elevated, and only about 8 m when buried.
- Uphill and downhill. On a slope, an elevated charge is closer to the snow above it than to the snow below it. The calculator works out the difference for any slope angle.
- Snow conditions. Dry slab, hard slab and wet snow respond very differently. In wet snow, the effect is limited to about 10 m around the crater, whatever the charge size.
- Elevation and temperature. Thin mountain air lowers the blast pressure. The same charge travels about 15% as far at Loveland Pass as at sea level.
- Safety distances. Air-blast distances for hearing protection and for windows and structures.
It works in both US and metric units, and comes with a step-by-step manual with diagrams and worked examples.
Who it is for
New blasters use it to learn why placement matters more than charge size. Experienced avalanche blasters use it to compare options before the shot: how much explosive to use, how high, and how far apart for the slope and snow in front of them. Here is an example from our PETS_Avalanche_Blast_Calculator to help predict pressure and triggering zones as well as the optimum amount of explosives used for the artificial trigger avalanche.
The PETS_Avalanche_Blast_Calculator is a planning and training aid. It does not replace your judgment, your operating plan, or the regulations, and no calculation can confirm that a slope is safe.
Training with the calculator
We offer the calculator together with our avalanche control explosives training, online or in person. Contact Petr Explosives Group at petrexplosivesgroup.com to schedule training for your team. Please contact us if you have any questions or are interested in our training program. vp***@*****************up.com
Petr Explosives Group · Practical Explosives Training School
