Avalanche Transceiver Interference

In the modern 24/7 world, most  peoples’ lifestyles depend heavily on consumer electronics – and in particular the mobile phone.  This presents us with a problem when backcountry skiing, as all electronic devices create electrical interference that can compromise the function of your avalanche transceiver.
This is a well known and researched problem, but not many backcountry skiers follow the latest advice – either through lack of education, or an unwillingness to change their personal behaviour (I’ve encountered both amongst off piste skiers!)
There are plenty of situations where it might be a good idea, or necessary to use electronic items whilst backcountry skiing – such as a GPS for navigation in poor visibility etc. 
However, much of the time it’s done out of habit, or it’s a choice.  We are all used to switching off phones in a wide variety of educational, work and social situations (meetings, lectures, cinema/theatre etc), so switching your phone off is no big deal.  Take it as a chance to escape your digital life for a few hours in a beautiful mountain environment – you can always Tweet/Insta/FB all about it afterwards! 
Seriously though, if you want to take photos and video, then do so in a safe place and remember to switch your device off fully between shots.  Likewise, if you want to check your phone for messages/updates during the day, then do so in a safe place, eg at lunchtime etc and remember to switch your phone off again before resuming skiing. 

The message is, plan to reduce your use of electronic devices whilst backcountry skiing, only turn them on when needed, always carry them well away from your transceiver and by default, it’s safest to keep them switched off. 

*NB Off means completely switched off in this instance – airplane mode won’t help here, as it’s the touch screen that causes most interference. 
**In an avalanche incident, if rescue services are available close by (ie less than 15 minutes away) and you decide to call for a rescue, then it’s Ok to keep one ‘rescue phone’ switched on, so long as you keep this phone well away (100m or more) from the search area – clearly, this decision also removes 1 rescuer from the search. 
***Very low power electronic devices (eg flat battery watches) are Ok to wear on the wrist – if the device needs regular recharging however, don’t wear it on your wrist! 
Cameras – if you want good photos, it’s still best to buy yourself a decent camera, rather than relying on your phone! Lift Passes – these have been tested and found to be Ok. 
The Problem
The first incident where electronic interference from a mobile phone is thought to have contributed to an avalanche fatality occurred in 2000 in the French resort of Pra Loup, when a well trained ski patroller failed to locate a buried colleague after over half an hour of searching.
Since then, the effect of interference on avalanche transceivers by consumer electronics, radios and metal objects has been the subject of a number of scientific studies (see references below).
If you are interested and of a scientific background, the papers make interesting reading – but to save you wading through it all, the summary findings are that devices with touch screens cause the biggest problems (which in itself is a problem, as practically everything is now going over to touchscreen!) – and most especially, modern smart phones.
NB Ski lifts,  electrical power lines and approaching storms are also known to cause interference, so you need to be aware of your surroundings too.

The Effects
The possible effects are summarized below: 
As a victim: In send (transmit) mode, if you have anything metal, magnetic or electronic too close to your transceiver it can reduce it’s output range by up to 30% – which means the rescuers may need to reduce their search strip width and get closer to you before picking up a signal – ie if you have your phone switched on and get buried in an avalanche, you could be harder to find.
As a rescuer: In search (receive) mode, electronic interference is a much bigger issue, as initially the transceiver is trying to pick out a very weak, distant signal from the background noise.  Switched on electronic items within 50cm of your transceiver can result in a reduced search range, so you may have to narrow your search strip width and interference can also sometimes create false distance/direction readings or problems with processing multiple burials.

So, how to proceed? Well, it might help first if we look at the transceiver manufacturers guidelines, which are based on the findings of this research and their own studies.

Transceiver Manufacturers Recommendations
All of the major transceiver manufacturers recommend keeping any switched on mobile phone and other electronics, magnets and metal objects at least 20cm away from your transceiver when it’s in send (transmit) mode (ie when skiing) and any switched on electronics and magnets at least 50cm away from your transceiver when it’s in search (receive) mode (ie in a rescue). A lot of people read this casually and think: “Ok, I can keep my phone switched on, so long as I keep it in a pocket well away from my transceiver – problem solved, lets go skiing!”
However, it’s not quite as simple as that – as they also advise you to keep electronic items switched off whenever possible whilst off piste skiing.  Some of the reasons behind this are explained below:

First problem: in reality, it’s not actually possible to keep your phone in a pocket and over 50cm away from your transceiver whilst doing a transceiver search (this has been studied – Orloff, Big Sky Ski Patrol, 2016)  To be over 50cm away, your phone needs to be in your rucsac, in which case you might as well switch it off…

Second problem: stressed people with infrequent training are forgetful: it’s been found that the average cognitive functioning level of an adult recreational skier faced with an avalanche incident, is that of an 8 year old.  Would you 100% trust an 8 year old to remember to switch their phone off along with any other electronic items, before starting a transceiver search?

Third problem: Multiple sources of interference add up –  so if you are carrying a switched on phone, wearing a GPS watch and using a Gopro action cam, then the combined interference of all these items will be far greater.
Also, the combined interference of several team members carrying switched on electrical items during a search can create problems in the final pinpoint search phase,  when team members are closer together, preparing to probe and dig.
So how big a problem is this? 
​Currently, we’ve identified the problem and how to avoid it, but at the time of writing there aren’t any detailed statistics available regarding the number of fatalities that electronic interference may have contributed towards.  What we do know however, is that it was first discovered following a failed transceiver search and a fatality, so it’s definitely a serious issue.
Anecdotally, some transceiver models appear more affected by interference than others – so depending on the situation you face, if there is electronic interference present, your transceiver may still take you to the victim, but there’s a chance that it won’t.  Given your luck has just run out badly already and the grim statistic is that 50% of fully buried victims are not actually pulled out alive (due not being dug out in time, injury etc) – then you don’t want to shorten the odds even further.  Ie a failed transceiver search has a very high consequence (death!) – so although the risk may be small, it’s important to reduce any known factors that may cause a search to fail..
Therefore the clear message is: minimise your use of electronic devices whilst backcountry skiing, only turn them on when needed, always carry them well away from your transceiver and by default, it’s safest to keep them switched off.

Latest Transceiver Developments
Transceiver manufacturers are well aware of the problem and working to mitigate against the effects of interference problems. 
Some of the newest transceiver models can now detect interference and warn the user – both the new Baryvox and Baryvox S models from Mammut can do this. 
If interference is detected by the transceiver, a warning icon, or message is displayed, giving instructions to the user – eg ‘move sources of interference away from the transceiver’, ‘reduce search strip width to 20 metres’ etc.

With older models you don’t get any warning if interference is causing a problem – the transceiver either fails to detect a signal when it should, ‘detects’ a false signal where non exists, or gets confused and takes you in the wrong direction…

What about Guides and Rescuers?
Ski Professionals are not immune from the problem – Guides need to consider how they manage and use electronic devices during the course of their work: for instance, having a ‘phones switched off’ rule within the group, or having just one device switched on for navigation etc. 
Also for rescue, safety and coordination purposes, many guides/patrollers/rescuers may be required to have radios (but less often phones) switched on at work or during a search or rescue, which clearly throws up problems.  An investigation into Ski Patrol radios found that the units being tested produced less interference than smartphones, but their effects still need to be taken into account. 
Ski professionals already start with high levels of technical experience and search proficiency, so with further training can be taught to identify, manage and overcome interference problems during searches by  using alternative techniques (eg by switching to analogue mode in high interference polluted areas etc). 
If you don’t have an analogue facility on your transceiver (only the top end ‘pro’ models have it) and you aren’t experienced and proficient with analogue search techniques (eg you’ve had professional training, or practice every week) then this is not a viable option for most recreational skiers.

My own working protocol
As a guide, I brief my group on transceiver interference issues at the start of each weeks skiing and on the first morning, I ask everyone to switch their phones off, so we can do a full transceiver range and function check before going skiing.
Despite this, about 2-3 times a year I come across a transceiver that’s exhibiting either reduced search or send range, or I hear unusual amounts of background noise/ghost signals etc when using analogue mode for the range tests.  To date, on every single occasion this has happened, the problem has been tracked down to a mobile phone still being switched on in someones pocket, or another electronic device close to the transceiver.
Clearly, most people want to take photos/video of their trip – so I ask folk to switch phones off between shots, just like I do with my camera.  I also take a lot of photos and video myself, with a good dedicated camera – so that everyone comes away with plenty of good photos of the trip. 
Reminders after lunch/photo sessions complete the daily routine.
I carry a phone/radio/sat phone for communication on all of the ski touring holidays that I guide, but it stays in my pack switched off until needed (in very cold, weather I keep it switched off in a pocket >20cm away from my transceiver – see electronics management notes below). 
​Like technology, working norms and safety protocols evolve over time: for instance, the “put all electronics in your backpack and check that your phone is switched off before starting a transceiver search.” instruction is a new one, in response to the increasing number of touchscreen electronic devices that people now use and wear all the time.

Managing Lithium Batteries in Cold Weather
All Lithium batteries used in phones and modern electronic devices have reduced capacity and run down more quickly at low temperatures, so keeping them warm and using devices with a larger battery, or carrying spares may be necessary when you are operating in low temperatures. 
Keeping the device warm and switched off when not in use is the obvious thing to do.  For items like cameras; carrying spare, warm batteries in a pocket is also a good plan and for phones in particular, switching to airplane mode massively increases the battery life, as does switching to low power mode and keeping the the screen switched off as much as possible. 
With regards to transceiver interference; so long as the device is switched off, then you can treat it the same as a metal object – so there’s no problem keeping your phone in a pocket in cold weather to keep the battery warm; just make sure that you carry it >20cm from your transceiver. 
At -5 to -10C Lithium batteries used in phones, modern GPS units and cameras lose about 15-25% of their capacity (they also run down more quickly when used at low temperatures).  Older style, non touch screen GPS units generally work fine at this temperature range. Phones however, are rated for use at specific temperature ranges which can vary between brands and models.  This means that some phones are more susceptible to failure in the cold than others. 
Iphones for instance are rated for use between 0C and 35C, which means they can (and sometimes do!) fail at temperatures of -5 to -10C.  Older Samsung phones have been tested and found to work much better than this at lower temperatures – however, I’ve found no test results for their current models. 
The problem gets worse at progressively lower temperatures: at -20C lithium batteries can lose up to 50% of their capacity and also discharge more quickly.  At these temperatures, even a warm smartphone will quickly fail once exposed to the elements, unless it’s well protected and only used for a minute or two.  Non touchscreen GPS units fare better at this  temperature range, but should still be kept as warm as possible and ideally used intermittently to ‘check and confirm position’ rather than as a primary, continuous navigation tool unless absolutely necessary.  Spare warm batteries should always be carried. 
Some ruggedized ‘tough’ phones on the other hand, are rated down to -20C,  so these could be an option to explore for low temperature use. 
Many people and certainly most Guides, carry power packs on longer trips like skiing the Haute Route, in order to recharge phones and other electrical devices. However, it’s very important to know that you shouldn’t ever recharge a Lithium battery when the battery temperature is below 0C – this is a big no-no, as it will permanently damage the battery (in a worse case scenario, the battery could split and catch fire some time later!) 
Therefore, if you have a phone or other electronic device that’s died on you whilst on the hill due to the cold, then you absolutely must re warm the device and the power pack first, before plugging one to the other! This also means that you shouldn’t take a cold phone or other device out of your rucsac at the end of the day and start recharging it immediately – you need to re warm the device for a few minutes, so that the battery is above 0C before you start recharging it. 
There’s plenty of info online explaining the chemistry behind this problem – it’s a well known issue amongst battery scientists, but not the public! 
On the flip side though, Glenmore Lodge (the Scottish National Mountain Centre) instructors have had some success using power packs as remote battery packs on the hill – ie placing a power pack in a warm inside pocket, then connecting it to a phone in an outer pocket for use on the hill.  I’m not sure what this may be doing to the Lithium battery inside the phone at low temperatures (see comments above!) but it has been found to work at typical Scottish winter temps (ie at around, or a few degrees below, freezing).
​
Some Thoughts on Navigation
We are fast reaching a tipping point where electronic, GPS based devices are becoming one of the most common means of mountain navigation.  GPS is super accurate and many smartphone apps in particular, are very easy to use, even for inexperienced navigators.  With the ability to share routes via GPX files and the opportunity to cross reference this information with online avalanche forecasts and terrain maps etc, this technology has great benefits for skier safety when it’s used intelligently. 
However, when not used intelligently it also has the potential to make things less safe.  We’ve all met that clueless, poorly dressed couple getting cold and wet in the mist with an iphone, who would never have gotten so far up the mountain were it not for the phone – and who clearly wouldn’t be able to deal with any problem, or get themselves down safely if the batteries ran out…
In poor weather or reduced visibility, if you are only confident enough to follow a particular route because you have a phone or GPS for navigation, then maybe you should ask yourself whether you are making things safer or actually more dangerous  – most likely the avalanche risk will be higher, so you need to have done a lot of extra detailed planning and maybe you should be carrying some extra safety kit etc, rather than just relying on the phone.  I know guides who’ve fallen into the trap of carrying on ‘because I’ve got a GPS’ and then regretted it, so this is a problem for all of us, not just the inexperienced. 
There’s a famous story about a German guide explaining to a pushy foreign client why it wasn’t safe to leave the hut in a whiteout: the guy had questioned why the guide couldn’t just use his GPS to navigate safely up the glacier – to which the reply came: “A GPS is for getting yourself out of ze s**t, not into ze s**t!” 
Apart from transceiver interference, the other issue we’ve talked about with electronics is battery life and in particular, battery reliability at cold temperatures.  I could easily use a smartphone or GPS to navigate all of the time (and indeed, many guides do!) – but in most conditions,  I personally still choose to use a map and compass for day to day navigation, as it’s great practice and the batteries last a lifetime!  On any tour, you should still be carrying a map and compass and know how to use them – and regular practice is the best way to keep your skills up.
Personally, I only use of my GPS in situations where I know it will have a positive impact on speed and safety.  As I’m quite handy with a map and compass, this means infrequently – but if you need to use yours more often, then clearly make use of it.  However, it’s not a good idea to rely solely on your mobile phone as your main (or only!) navigation device – as apart from issues with cold temperatures,  you are also running down the batteries on your principle emergency communication device at the same time…
Finally – there’s an amazing amount of great avalanche safety information available via smartphone apps and I use them every day, so please make use of this  – but be aware that most of this information is best used as a planning tool before you set foot on the mountain.  ie it’s not good to be measuring slope angles with your phone, or looking at a phone app ‘danger heat map’ in some critical spot in avalanche terrain, trying to make a ‘go-no go’ decision – the planning and decision making should have been done well before you set foot on the slope!

References:Barkhausen “The Effect of External Interference on Avalanche Transceiver Functionality”
Meister and Dammert “Effect of consumer electronics on avalanche transceivers”
Genswein, Atkins et al. “Recommendation on how to avoid interference issues in companion and organised avalanche rescue”
Orloff “Distance between Electronic Devices and Avalanche Transceivers on a Professional Ski Patrol”
​Forrer, Muller, Dammert “The Effect of Communication Equipment on Avalanche Transceivers”