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avalanche & mountaineering BY HENRY BALLARD, DALE ATKINS, AND LIN BALLARD zoning in on new probing tactics R Researchers are constantly looking for better ways to find avalanche victims, but the age-old method of probing will always be necessary in some situations. While variations of a standard probe search system have been in wide use for about four decades, recent studies suggest that the original projection for the probability of detection (POD) of 70 percent for an average victim was far too optimistic. Therefore, as researchers in the field, we’ve been busily crunching numbers and creating computer models of bodies lodged in avalanches in order to devise more effective probing tactics. A big part of the problem with historical probe models is that the “targets” incorporated into the original calculations in use in the 1960s and ’70s did not adequately represent the human form. The victim was depicted by a rectangle that, depending on whether the victim was in a vertical, prone/supine, or sideways orientation, could be of varying size. While the target was modified in the 1990s into more of an elliptical shape, neither truly took into account the full range of positions in which a body can come to rest in the wake of a snowslide. A more realistic model of an avalanche victim’s body shape and positioning has given us the opportunity to improve the results of probing. Over the past year, we developed a computer program named PROBE, which takes into consideration the dimensions of an average human body as well as such variables as resting location and dimensional positioning under the snow. By incorporating a more realistic victim into an examination of today’s most commonly used probe/grid procedures, we’ve collected data that suggest certain modifications in traditional search procedures Co-author Lin Ballard (facing camera) and fellow members of the Bryan Mountain Nordic Ski Patrol demonstrate proper probing aided by a guidon cord marked at 50-cm intervals. can improve probabilities of detection. The notion of an improved set of calculations for the victim set in motion the search for a more effective probing procedure, and the findings of this research were presented at the International Snow Science Workshop in September 2004 in Jackson Hole, Wyoming. Here’s a basic summary of that presentation. Those seeking more details will find the full study at http://geosurvey.state.co.us/avalanche/Portals/0/3HPS_ISSW_2004.pdf. HENRY BALLARD 44 Ski Patrol Magazine | Winter 2005
avalanche & mountaineering table 1 Comparisons of targets (approximately to scale) and PODs for traditional 75 by 70 cm grids. (A typical body generated by PROBE will have a surface area in the prone/supine position of between 0.4 and 0.5 m 2 .) Orientation Target area Square body, Square Elliptical body Ellipse PROBE PROBE m 2 aligned to grid (1976) POD (1997) POD (2004) POD Vertical 0.10 20% 19% 22% Prone/ Supine 0.50 95% 75% 74% Side 0.40 76% 63% 49% Average 0.37 70% n/a n/a 59% WHY PROBE? While some have suggested that probing is antiquated and inefficient, it’s still the best method for finding a victim when other methods have been exhausted or are not immediately available. Even with a relatively high POD, the slow and arduous probing process can still be more than a “recovery” procedure, particularly considering that 14 percent of victims located by probing are found alive. While immediate search options such as rescue dogs, beacon tracking, and the use of electronic systems such as RECCO (a European avalanche victim-locating system now making inroads in the United States) certainly produce more successful results in terms of making a live rescue, the fact is that not all victims wear beacons, and dogs and search teams often take time to mobilize. For the foreseeable future, then, rescuers will have to probe for victims and need to know how to use the practice to its best advantage. Although there’s evidence that shepherds in the Caucasus Mountains used their staffs as impromptu probing poles more than 2000 years ago, organized probe line strategies didn’t develop until the 18th century, starting in Europe and eventually making their way to the United States. In the middle of the 20th century, the “state of the art” of probing technique was presented in the Avalanche Handbook, published by the U.S. Forest Service in 1952. Written by Felix Koziol and NSP’s legendary avalanche guru Monty Atwater, the book included specific language that probers should be “...spaced shoulder to shoulder and probe every square foot.” By the late 1970s search and rescue personnel had settled on a probe line strategy-based on a 75- by 70-cm grid. A body measurement of 0.4 square meters aligned with the probing grid resulted in a projected POD of 76 percent for a body on its side (table 1). An “average” body of .37 square meters resulted in a POD of 70 percent. For the actual calculations, refer to our original paper on the aforementioned website. A modification of a technique introduced in the 1970s—which called for searchers to probe twice per step rather than just once (called the open order coarse probe)—enhanced efficiency of the coarse probe. Twenty years later, in a paper presented at the 1996 International Snow Science Workshop in Banff, Canada, authors Tim Auger and Bruce Jamieson made a case for a three-hole-per-step (3HPS) technique that suggested placing rescuers 175 cm apart and probing directly in front of their bodies as well as 50 cm to the right and left of that center probe. The probe pole could be angled out 10 degrees to the sides to allow the searcher to quickly and easily perform two additional probes for increased coverage from the single position. A year after the introduction of the 3HPS method, Auger and Jamieson replaced the square model with an elliptical model in an effort to better represent a victim’s body in the space beneath the snow. In terms of creating a realistic image of a person buried in an avalanche, it was believed that the new calculations for the victim’s body (in terms of space and positioning) were closer to reality than the 0.4-square-meter measurement used in the old model. Factoring in the elliptical model of a human body, the researchers found that the probability of detection within the traditional 75- by 70-cm grid was reduced (again, see table 1). Researchers assumed that the 3HPS method improved the efficiency of probing, but a study conducted in 2000 revealed that the insertion of probes at an angle is ill advised because the procedure literally allows “too much room” for error. The results of the study determined that angled probes leave large unprobed gaps. Research suggests that probes at 10 degrees to each side cross paths with the probes of adjacent searches at a depth of about 210 cm and leave large un-probed gaps on the first pass. Thus, there are clear indications that vertical probing provides the best opportunity for finding victims. Fortunately, the NSP never adopted or recommended the angled probing technique, and to the best of our knowledge it is not in common usage anywhere today. OUR EXPERIMENT Rather than employing the simple geometric forms used in past computergenerated models of victims and their CONTINUED W inte r 2005 | Ski Patrol Magazine 45
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