Multivictim searches, and the best transceiver is?
Around this time of year we begin to see the results of “Beacon Beauty Pageants” as someone launches tests of the various avalanche transceivers on the market. The tests are normally pretty straightforward. Hide a beacon under snow and then time how long it takes people to find it. So far, so simple.
The SLF (Swiss Avalanche Research Institute) and ANENA (French National Association of the Study of Snow and Avalanches) decided to get a bit more in depth. Last spring they carried out a series of tests using different groups of users and the results were published at the International Snow Science Workshop this autumn.
The SLF/ANENA tests put a particular emphasis on multi-victim searches. Although rare they cause particular problems for rescuers even with modern digital avalanche transceivers. 18% of incidents reported to the SLF where a victim was completed buried were multivictim (2 or more) scenarios. The tests were split into two sections: beginners/intermediate, who probably represent the majority of users, and advanced (club instructors, guides, pisteurs, rescue workers). The different types of user were given transceivers adapted to their level. All the transceivers were three antenna designs with digital output. The Arva Axis, Link and Mammut Pulse also have a raw analog function by-passing the beacon’s own signal processing.
The beginner group tested 5 mid-level transceivers: Arva Axis, Mammut Element, Ortovox 3+, Pieps DSP Tour, Tracker 2. The advanced users tested the: Arva Link, Mammut Pulse, Ortovox S1+, Pieps DSP.
For the beginner test the park used transmitters with a short, 100ms pulse with a random pause between 950 - 1050 ms to limit problems with signals masking each other. Transmit frequencies were very close to the 457kHz standard. All the transmitters were buried with optimal antenna orientation for maximum signal strength. The test area was 50 m.sq. On average an avalanche deposit measures 80x100m where a victim is completely buried so this is a fairly small search area with almost no primary search phase required. This favoured transceivers with limited search range, like the BCA Tracker II, for the time to first victim.
For the advanced test the transmitters were buried at least one meter underground protected by a 50x70cm plank with some buried at 2 to 2.3 meters. The beacons were located in four separate search areas of 100m.sq. Two areas has a basic multi-victim scenario with 3 victims with a similar configuration to the beginner tests. In one test area the carrier signal of one transmitter was -50Hz, still within the +/- 80Hz tolerance allowed by the ETS 300718 standard. Another transmitter was -100Hz, outside the current standard but just within the tolerance allowed by the old standard (ie an Old Ortovox F1 still widely used by club groups). This reflects the reality where transceivers’ carriers often drift below 457kHz. In the other area a beacon was +30 Hz.
The two other areas had complex multi-victim problems to solve with four active beacons, two in close proximity with a long pulse leading to frequent masking of the signals. The aim was to see if searchers could detect the problem and switch to an alternative search strategy (microstrips, 3 circles etc).
All the searchers received training from representatives of each transceiver company. This focussed on a basic introduction to each transceiver for the beginners to and in depth look at mult-victim strategies for advanced users.
The beginners were all able to find the first beacon within 2 minutes. Problems began with the second beacon, in 5 out of 40 cases the second beacon was not found in the required time and things got worse when searching for the 3rd target where four of the five transceiver had trouble finding the victim.
The tests showed that there were considerable differences between the various transceivers in multi-victim scenarios. The fastest transceiver to the first target was the BCA Tracker 2, confirming BCA’s marketing that for beginners, at least, simple is better.
Overall, and including 2nd and 3rd victims the Mammut Element came out best with fast search times and only 1 victim missed on the 3rd target. The Pieps DSP Tour and Arva Axis had problems with the marking function which caused particular difficulties with 3 victim searches. The Tracker 2 out perfomed the Pieps and Arva and even came in just ahead of the Ortovox 3+.
The advanced users were all able to find the first beacon in the required time with the Mammut Pulse being the strongest performer. Only the most complex tests posed real problems for the searchers and then only when looking for the 3rd and 4th victim. Advanced users were able to find the beacons even where the marking function failed to work properly. They had most problems using the marking function of the DSP Pieps but the differences between the transceiver types were marginal. Professional rescue workers were, on average, 20% faster than guides or club instructors.
It is clear that Beginner and Intermediate users are much more dependent on the ease of use and tolerance of their transceiver. Their lack of experience, training level and the limitations of the transceiver made applying alternative search strategies difficult once they reached the limit of their device. There is a clear difference in the speed of professional rescue workers and other users.
If you are worried about multi-victim searches but are on a limited budget then the Mammut Element is a good investment. It would suit professionals taking exams where setting up complex searches with faulty beacons is beyond the scope of the organizers. Recreational users would also be well served by the BCA Tracker II. It is not as strong performer where 3 or more victims are buried in proximity but is extremely rapid to find a single victim and reasonable on 2 victim searches. For Pros, who have the training to exploit the advanced features, the Mammut Pulse is a very strong performer.
Posted by davidof
on Wednesday, 23 January, 2013 at 07:27 PM
Almost all modern digital beacons are all pretty good at simple single victim searches. This means the beacon companies need a way of differentiating their products. In recent years this seems to have been achieved by adding multi-victim features with mask function.
1) Surveys & tests, such as the one above, ignore the time it will take to dig a victim out. Ideally once a victim is located you turn their beacon off ASAP. Locating 4 beacons in 10 minutes is no use if you cant dig them out!
2) Multi-victim features will probably only be used when there are 2+ victims AND also 2+ searchers. Even in this scenario would the searchers be better concentrating all efforts on digging out the first victim before trying to locate the second ?
3) Due to existing standards the mask function will never work perfectly. Therefore to be 100% competent requires training and practice in 3 circle techniques / grid techinques etc.
IMHO there is now a danger the multi-victim feature is wrongly used as the main differentiator between models. Better to concentrate on the basics (unless perhaps if your a professional ski patroller or UIAGM etc)
Posted by on Tuesday, 05 February, 2013 at 09:22 AM
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