Applying Wearable Sensors to Avalanche Rescue: First Experiences with a Novel Avalanche Beacon

Florian Michahelles1, Peter Matter1, Albrecht Schmidt2, Bernt Schiele1

1Perceptual Computing & Computer Vision Group, ETH Zurich. {michahel, pmatter, schiele}@inf.ethz.ch 2Computing Department, Lancaster University, LA1 4YR, UK. albrecht@comp.lancs.ac.uk

Keywords situation-aware, wearable-sensing, personal assistance, avalanche rescue, mobile application, wearable computing

Abstract We present a novel approach to enhance avalanche companion rescue using wearable sensing technologies. The time to find and extricate victims is most crucial: once buried by an avalanche, survival chances drop dramatically already after the first 15 minutes. Current technology offers only information on the location of a single victim, however statistics show that in many case there are multiple victims. In our research we address this issue and also investigate how the use of wearable sensors can further enhance such devices. We report on experiments using sensors to measure vital signs and environmental conditions and their suitability for avalanche rescue. Visualization for this type of application is addressed and two design sketches, both visualizing multiple victims and urgency, are presented. The architecture of current devices is extended by components to integrate these additional functions. We report on prototypical implementation of an avalanche beacon supporting multiple victims and visualization of vital signs. This prototype was used for further experiments and offered a basis for participatory evaluation with practitioners in the field. A short overview of these results is presented.

1 Introduction There is an on-going trend towards out of bound (off-piste) skiing. Recreationists go beyond their limits, underestimate the danger of avalanches and risk their lives without the appropriate awareness of avalanche risks [1]. Accordingly, the

number of alpine recreationists in backcountry terrain, such as skiers, snowboarders, ice-climbers, etc., has increased in the last years [2] [3]. Statistical analysis of avalanche accidents during the last 30 years [4] has revealed that successful avalanche rescue has to aim at rescuing victims within the first 15 minutes. Avalanche survival is a monotonously decreasing function over time and after 15 minutes there is the biggest decline from 90% to 30%. It is noteworthy, that three quarters of all avalanche victims die from asphyxiation, only one quarter is killed from trauma. Consequently mountain clubs, such as the Swiss Alpine Club or the Canadian Mountain Rescue Association, put enormous efforts into educational programs on avalanche awareness and companion rescue operations. Simultaneously, beacon technology is widely used by recreationists. Worn by the mountaineers these electronic devices enable survivors and witnesses of an avalanche to start immediate search and rescue operations. This yields survival chances four times as high as in case of organized rescue [5], which is often too late. This paper concentrates on enhancing existing avalanche beacons with wearable sensors. Current devices only provide directions for finding victims. However, state of the art in wearable sensing suggests more opportunities: sensors can reveal emotional states [6], vital sign data [7], motion and orientation patterns [8] etc.. We believe that providing information on victims’ physical states at an avalanche site to rescuers allows much better resource allocation to the most urgent victims. Further, logging this information in a blackbox device, as used in today’s airplanes, could record the sequence of events during an avalanche release for basic avalanche studies or legal actions.

In Section 2 today’s beacon technology is reviewed. Section 3 investigates opportunities of improving today’s technology through sensing technology based on practical experience. Section 4 shows how the sensed information can be presented to rescuers visually. In section 5, an architecture design demonstrates the integration of wearable sensing into existing beacon technology, and section 6 describes an implemented prototype as a result. In section 7, the concept is discussed with avalanche experts and summarized in section 8.

2 Analysis As professional aid may arrive too late, today mountaineers are trained in companion rescue.

2.1 Companion Rescue The standard companion rescue procedure - as it is advertised today - comprises three steps. First, the victims have to be localized in the avalanche. With avalanche beacons search should take no longer than 3 to 5 minutes. As a second step, extricating a localized victim with shovels should not take more than 10 to 15 minutes. Extrication has not only to be quick, but also be performed with care: victims could be injured by the shovels and air-pockets, victims' protection against asphyxiation, could be destroyed. Rescuers today do not know how victims are orientated in the snow. The third step is to execute first aid: opening respiratory tracts and avoiding hypothermia. At this point professional aid should take over. The entire rescue process has to be as fast as possible in order to maximize survival chances. Due to these severe time constraints, rescue resources will be always limited in practice. Further, rescuers are in an emergency situation and very stressed.

2.2 Current Technology Today, beacon technology only assists during search. Beacon devices operate on 457 kHz long wave frequency, which has become an international standard. Microprocessors on the devices can calculate distance and direction to a single victim from the emitted dipole flux pattern [9]. By that, the devices can guide the rescuer to the victim either through arrows on a display or sounds with rising volume as the rescuer approaches the victim. Usually, a range of 80m

can be achieved. Batteries last up to 300h. By default, devices operate as senders and can be switched to receive mode to initiate rescue operations. Direction and a rough estimation of the distance that is all beacons provide today. However, much more support would be desired:

• knowledge about the state of the victims, survival chances, urgency, vital sign functions

• support for rescuing multiple people • orientation of the victim in the snow • burial depth of the victim

2.3 Advancing the Technology In this paper we investigate opportunities of using wearable sensors for reporting information on vital sign functions. Our approach is to automate triage [10], as today emergency physicists maximize survival chances by prioritization. This enables also non-professional companion rescuers to improve their rescue strategies. Further, we apply accelerometers to report victims’ orientation in the snow. This information helps rescuers to avoid injuries during shoveling, provides faster access to respiratory tracts and preserves possible existing air-pockets. For the representation of sensor information, we develop different visualization schemes which could be integrated into today’s devices.

3 Sensing Today’s wearable technology offers a variety of sensors, which can be attached to the human body in a non-invasive matter for continuous readings and measurements.

3.1 Vital Sign Data Sensors which provide information about vital sign data are of major interest for avalanche rescue: Mountain medicine has developed a so-called triage-scheme for emergency physicists. Based upon different vital sign data, such as heart rate, respiration activity and consciousness [11] derives different urgency states and determines appropriate first aid operations [12]: Missing heart rate requires manual chest compression, absence of respiration activity demands rescue breathing, and unconsciousness has to be treated by anti-shock therapy. As rescue operations differ in rescue resources, e.g. chest compression requires two trained rescuers, anti-shock therapy

only one low-skilled rescuer, knowledge on victims' vital sign functions enables rescuers to foresee upcoming rescue procedures and allocate rescuers among victims more properly. Today, triage is reserved for professional aid, as triage is rather complex and requires medical experience which is usually not available for non-professional companion rescuers. Automation of triage would also provide companion rescuers with decision tool that helps to focus on most urgent victims first. Currently, triage is delayed until victims have been extricated and rescuers get access to them. Instead, wearable sensing attached to the human body can provide continuous sensors readings and share the awareness of emergency with surrounding rescuers much earlier. Evidence of life signs may also motivate rescuers and drive rescue of remaining victims even under harsh conditions. Finally, vital functions of victims could also be communicated to professional rescue service without human intervention.

3.2 Sensors According to the triage scheme [11] used in avalanche rescue the primary selection criteria are heart rate and respiration activity. Oximeters, which have a firm place in everyday clinical practice [13], offer a non-invasive way of measuring heart rate and blood oxygen saturation. Attached to one's finger, toe or forehead, the ratio of the fluctuation of red and infrared lights caused by hemoglobin - the oxygen carrier in human blood - is used to calculate the heart rate and oxygen blood saturation SpO2.

Fig. 1: Oximeter measurements We tested different placements of the oximeter: forehead, finger tips and toe. Only the toe turned out to be appropriate in mountaineering: Today's ski and hiking boots are well isolated and can shelter the sensor from damage and loss. Loss of boots, in contrast to gloves and hats in avalanches

is very rare. We have run several tests with skiers and snowboarders and could achieve reasonable measurements of heart rate and oxygen blood saturation, as shown in Figure 1. Further, subjects reported that the sensor would not have disturbed them during their activities, once wrapped around toe or finger, they soon forget about the sensor.

However, we are aware of the fact that severe cold may cause retreat of blood from the extremities, referred to as centralization, such that peripheral measurements at the toe may get unreliable under harsh conditions. Alternatively wearable ECG [14] provides heart rate measurements through electrodes attached to the chest. The advantage of this approach to oximetry is the robustness against centralization as the electrodes are very close to the heart. However, it has to be evaluated how well electrodes can be integrated into textiles in order to lower mounting efforts and to avoid displacement of the sensors during an avalanche. A more promising way of detecting heart rate, are contact-free measurements through radar: Radar waves are emitted and frequency analysis of the reflected signal from human body reveals heart rate based on Doppler phenomena. Currently, this technology has been deployed for people detection in earth quakes and border controls. However, customization for on-body measurements could offer solution which is robust against both centralization and displacement, as this technique works contact less.

Fig. 2: test – respiration in air pocket Another important source of information is

the existence of air-pockets in the snow, closed air bubbles in front of mouth and nose, as they protect victims against asphyxiation up to 90 minutes [15]. Today, air-pocket detection is hardly possible, but both rescuers and physicists are interested in this phenomenon. In particular avoiding the accidental destruction of air-pockets during extrication is of interest. The existence air-pocket can also provide evidence for working

respiratory tracts. As an initial study, we investigated the use of oxygen sensors for air-pocket detection. For an initial assessment we measured oxygen concentration of breath activity in an artificial air-pocket and a plastic bag.

We applied an oxygen sensor from Fujikura [16] connected to an evaluation board from Pewatron [17] that measures oxygen concentration in per mil accuracy range. After a few minutes, the sensor reported measurements below 12%, which is significant deviation from normal 20,9% in the air. Then, we placed the sensor into a little snow, representing a more realistic air pocket, and instructed a test person to in- and exhale into that cave through a snorkel, see Figure 2. The measurements were very different from the ones with the plastic bag: Concentration did not drop below 16% and even relaxed to 20.9% after a few minutes. Further, we measured oxygen concentration in snow by covering a sensor with snow completely: the measurements are very close to 20.9% as in air. These results also agree with [18], which revealed that asphyxiation in snow is not due to lack of oxygen but rather due to the high concentration of carbon dioxide.

3.3 Experiences and First Results As a result, oxygen sensors did not appear as the appropriate method for air-pocket detection. However, in a closed system, as the Avalung [19] product, with tubes for oxygen supply in emergency, oxygen sensor may be used very well for reporting about respiratory activity. For air pocket detection, other sensors, such as distance measurements based on radar or infra-red, closely placed to mouth and nose in one’s collar seem to be more promising. Nevertheless, proper sensor placement remains crucial and difficult.

Fig. 3: testing - volunteer in snow cave As outlined before, knowledge about a victim’s orientation can be very helpful for rescuers during

extrication. Acceleration sensors are widely used in wearable sensing [8] [20] and have proven useful for motion detection. As accelerometers measure all means of acceleration, in the stationary case these sensors can report orientation derived from direction of gravity. We explored how a two-axis accelerometer [21] can be applied to detect the orientation of one’s spine, as shown in Figure 3. The orientation level can be well translated into information cues for rescuers, such as head up, head up side down or head vertical. Ideally, a number of sensors would be integrated into underwear shirts to prevent displaced and to achieve most reliable measurements through redundancy.

4 Visualization Avalanche rescue is a situation under immense pressure – companion rescuers, who are usually recreationists and not professionally educated rescuers, just survived a horrific accident and feel the pressure to help their comrades. Recent statistical analysis has shown that a surprisingly high percentage of victims get caught and completely buried in avalanches producing multiple burial scenarios [22]: 61% of all backcountry skiers who could not be found by visible parts were involved in a multiple burial situation. Multiple burial scenarios ask too much of most companion rescuers, support with avalanche beacons is not sufficient yet but necessary. Consequently, ease of use for an assisting device is key. Today’s devices still require lots of training: Some versions still guide the user with periodical beeps to the victim. However, changes in volume are very hard to separate for untrained users. Newer devices provide support with little arrows and rough distance estimates presented visually on a display. Accordingly, an avalanche beacon should, if at all, only require little training, its use has to be obvious even if explained long time ago. The user interface has to be very simple and should only use minimal navigation to keep complexity low. A visual user interface could help to make usage of avalanche beacons much easier.

4.1 Design Rational First, for multiple victim scenarios it is essential that the system allows discrimination between victims. Today, avalanche beacons only report the

occurrence of multiple signals, different sources are not isolated, such that interference between multiple signals can confuse the rescuer. Rescuers have to perform separation themselves and only follow the strongest signal by pin-pointing their device. The introduction of unique identifiers is rather a standardization problem among manufacturers than a technical challenge. Based upon that, visualization of the spatial distribution of all victims could give rescuers an overview about the emergency situation and enable them to allocate resources more properly. Though, absolute positions maybe difficult to achieve with today’s beacon technology, also relative positions to the rescuers location with direction and distance indications could improve today’s technology. Further, vital functions, air-pocket existence and orientation of the victim being searched should be visualized as well. Evidence of life signs may motivate rescuers and drive rescue of remaining victims especially under harsh conditions. Awareness on the physical state also helps to better foresee and plan upcoming rescue procedures. Presentation of the victim’s 3D orientation helps during extrication. Putting all available information of multiple victims into one single interface at once is too much: Avalanche rescue is a very cognitively demanding situation, rescuers must not be flooded with information. We propose separation in location and urgency. First, visual presentation of the victims’ spatial distribution enables the user to select to victims such that ways can be kept short. Secondly, separation in urgency provides rescuers with a global view on the emergency which allows better focus on the most urgent victims. The system presents an integrate view of several sensor readings.

4.2 Urgency measure A so-called urgency measure, as depicted in Figure 4, assigns an urgency level to each single victim, such that multiple victims can be aligned on a one-dimensional scale. Multiple victims can be compared much easier. The decision tree for automating triage scheme is defined as follows: Heart rate is the primary criterion, air-pocket is second, oxygen blood saturation is third (categories adopted from [23]), and orientation the fourth. In case of unavailable sensor information the fundamental concept is to always assume the worst case, e.g. if the oximeter

reports invalid measurements, absence of heart rate is assumed.

Fig. 4: Urgency measure

4.3 Two Designs For our prototypical implementation we designed a display, as depicted by Figure 5. As most people are used to read from left to the right, the urgency list starts with colored ID buttons, using the spectrum from red to green, at the left and continues to the right with less urgent victims.

Fig. 5: screen design of prototype The map below discriminates the victims by their location and ID. Especially in multiple burial scenarios with multiple rescuers the map helps to allocate resources more properly. Elapsed search time is indicated by a little timer below the map. For our prototype we used a handheld computer with a touch screen. Selecting a victim either by clicking on the urgency boxes or on the map reveals more detailed information on that person: direction and distance from the rescuer (e.g. 9m), heart rate (67), air-pocket existence (none), oxygen blood saturation (47%) and orientation (upright). We are aware of the costs of such a device and vulnerability to hazardous conditions, such as severe cold. However, the colored screen design allowed us to explore visual presentations more thoroughly and helped us to develop a more

lightweight design tailored for LCD devices, as partly embedded into today’s avalanche beacons already. Figure 6 shows a visualization scheme aimed for a simple LCD display. The first line shows the victims urgency, each represented by a bar at appropriate height. Victims may be selected by a button on the device and a triangle indicates the selection appropriately. Below, heart rate, direction, distance and orientation are displayed. Direction and distance are placed in the center as this is the most crucial information for search. Users are used to the arrow and distance measure from existing devices already.

Fig. 6: screen sketch for LCD displays

5 System Architecture & Functionality Looking at current systems and enhancing them with the technologies discusses leads to following architecture:

Fig. 7: Architecture Diagram An avalanche beacon is composed of a communication unit for sharing localization and sensor data of a victim with surrounding rescuers. Currently, avalanches beacon operate on the 457kHz international standard frequency, as long-wave has the advantage of little attenuation by objects, such as snow, metal, trees or rocks. Today, a 80m range [24] is achieved. Sensor data, such as vital sign functions, environmental data, such as air-pocket evidence, does not require more than two bytes: 1 byte for an unique identifier, another byte for coding heart rate, air pocket evidence and orientation (up-right, vertical, upside down) and calculated urgency. Standardization does not permit data modulation on the 457kHz signal.

Because of backward compatibility to older devices the standard must not be changed, but rather an additional frequency as a data carrier should be considered. Sensor information should be broadcasted continuously, but an update rate of ten seconds is sufficient. For searchers, the avalanche beacon requires a display for visualizing the received information. Finally, for post analysis memory in the devices could be helpful for recording the sequence of events during an avalanche accident.

6 Proof of concept – Implementation

Fig. 8: Prototype Setup For demonstrating and evaluating the concept we have developed a first prototype. For rapid prototyping purposes, various off-the-shelf components offered a fast and convenient approach. We integrated following three sensors: oximeter, oxygen sensor and accelerometer. We used a finger pulse oximeter [25], that can be easily attached to one's toe in a ski boot. The evaluation kit of the sensor itself can detect whether the sensor is mounted properly and the measurements are valid. The oxygen sensor [16] measures oxygen concentration in the environment in per mil accuracy range [17]. For orientation, we used an ADXL202 [21] accelerometer which was attached to a Smart-Its sensor-board [26] with a PIC micro-controller processing unit. All three sensors have been connected via a custom designed adapter board [27] to the serial port of a handheld pocket computer (IPAQ). The system itself is implemented on an IPAQ device. The colored touch screen interface provides high flexibility for exploring different visualizations: rapid prototyping enabled us discussing the concept with experts from the

field, see section 7. We have implemented the graphical user interface as proposed in section 4, which allows interaction by touch. Further, we integrated the urgency measure as outlined in section 4.2. Connectivity among different parties is provided by wireless LAN in peer to peer mode. Despite of the opportunities offered by a handheld computer, during implementation the restrictions posed by avalanche beacon technology were kept in mind: minimal bandwidth, battery life time, size, costs and visualization resources.

7 Discussion The prototype described in the previous section helped us to better motivate and demonstrate our concept to experts from the field by providing hands-on experience. In different focus groups and evaluation workshops with practitioners, such as emergency physicists, avalanche beacon developers and researchers from the Swiss Federal Institute for Snow and Avalanche Research we evaluated the concept [28]. Generally, we received positive feedback for the idea of applying wearable sensors to avalanche rescue, as this is completely new. Regarding sensing aspects emergency physicists argued that heart rate is a very significant vital sign – more accepted than oxygen blood saturation. The suggestion was to rather focus on heart rate only than trying to integrate diverse measures. Air pocket detection was very desired by both medical experts and avalanche researchers. However, reliable ways of detection remained unknown. Apart from only assisting rescue on site, blackbox functionality appeared to be very interesting for enriching statistics and further driving education in more appropriate rescue procedures. Ethical issues seemed to be very important as well. The concept of a system performing triage, which currently is only done by professional, offers new opportunities and has to be discussed thoroughly on a broader scale. Same applies to legal issues as responsibility for decision based on automated triage. Concerning several sensors it was agreed that an urgency measure is necessary. Even hiding the actual sensor readings from the rescuers completely and provision of calculated urgency only was raised. From a manufacturer’s point of view the use long-wave in another prototype appeared to be very important to make the prototype sound.

Further, it was mentioned that avalanche beacon market would be very small, 75000 devices per year sold world wide, which is a very limiting factor regarding development efforts. Users, approximately three millions in total, tend to use their devices for decades. Willingness for replacements would be very low. This fact suggests the focus on the development of add-on devices for existing beacons rather than revision of the beacons themselves. Using sensors not only for worst case scenarios as the actual accident, but also for monitoring health and fitness, as heart rate monitors do, may be another incentive for users to upgrade their devices.

8 Conclusion and Further Work In this paper we motivated the use of sensors in avalanche rescue by the importance of time during avalanche rescue and the black box view on buried avalanche victims today. We discussed and described how sensor technology can be used to provide rescuers with a valuable tool to enhance their decision ability on how to allocate their resources during rescue. An overview of meaningful sensors founded the basis for our system design. Further, we emphasized that displaying raw sensor measurements will not be appropriate and sufficient. Therefore we introduced an urgency measure to provide an integrated view of the urgency of all victims involved in an accident. A first prototype underlined the feasibility of our approach. We noticed a wide interest in the concept of applying sensors to avalanche rescue. Based on experiences gained from the existing prototype a new concept for sensing appeared to be necessary. Adding additional value to beacons, e.g. such as fitness monitoring, could help to justify higher costs for sensors augmented avalanche beacons. Integrating an avalanche warning capability, as proposed in [29], adds even more value for the mountaineer. First experiences with different sensors and placements determine future directions of extending our system. Investigating the use of Doppler radar could lead to better way of measuring heart rate. Radar may also help to detect the depth of burial which could give hints on how many rescuers have to be assigned to one victim in order to excavate them in time. Sensing technology could also trigger avalanche airbags or release an emergency call including vital sign functions and GPS position automatically.

Finally, we note that sharing awareness on individual's situations can also be applied to diverse fields ranging from military medicine over fitness monitoring to health monitoring for sick and elderly persons. In general, it would be a great achievement if A-Life could save at least some of the 150 lethal avalanche victims yearly.

Acknowledgements The Smart-Its project is funded in part by the Commission of the European Union under contract IST-2000-25428, and by the Swiss Federal Office for Education and Science (BBW 00.0281).

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