New study suggests that North American Avalanche survival time is half what was previously thought

Ten minute survival in western wet snow is shown by the study.

Dr. Pascal Haegeli, a researcher from Vancouver BC has recently published a study in the Canadian Medical Association Journal titled “Comparison of avalanche survival patterns in Canada and Switzerland.” There are several notable things to take away from this study.

1.     The survival time for a victim in an avalanche has been 18 minutes based on a study done in Switzerland in 1998. (Falk M, Brugger H, Adler-Kastner L. Avalanche survival chances. Nature 1994;368:21.) This 1998 study is not being dismissed. Differences between the types of snow, terrain, etc. are the cause for the discrepancies between the two studies.

This study says that avalanche survival time is probably only Ten (10) minutes.

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The Swiss study developed the avalanche survival curve based on the amount of time a person was buried.

The probability of survival remains above 91% during the first 18 minutes of burial (“survival phase”). This phase is followed by a precipitous drop to 34% between 19 and 35 minutes be – cause of asphyxiation of most people (“asphyxia phase”). Between 35 and 90 minutes, the survival curve levels out (“latent phase”) because of the survival of people with patent airways. Thereafter, survival drops again as those buried eventually succumb to lethal hypothermia complicated by progressive hypoxia and hypercapnia.

2.     There was no statistical difference between the overall survival rate of the Canadian study (Haegeli) and the Swiss study (Brugger).

…the Canadian survival curve showed lower chances of survival at all burial durations compared with the Swiss survival model, with a quicker drop in survival in the first 35 minutes and poorer survival associated with prolonged burials.

3.     Most Swiss avalanches occur above tree line. Most North American avalanches occur below the tree line. Trauma fatalities are significantly greater in North America.

In the Canadian sample, trauma accounted for more than half of the deaths among people extricated in the first 10 minutes (Figure 1), which highlights the strong influence of trauma on the early phases of the survival curve. The probability of survival at the end of the first 10 minutes was 77% in the overall survival curve for Canada, as compared with 86% in the asphyxia-only survival curve.

4.     There were statistically different survival chances between different climates in North America. Western (maritime) snow climates had shorter overall survival times. Western snow climates are characterized by wetter, heavier snow.

The survival curves for the transitional and maritime snow climates were characterized by a considerably earlier drop in survival compared with the curve for the continental snow climate.

The study also offered speculation that heavier denser snow prevented chest movement preventing the victim from breathing if buried.

Snow density is defined as the overall mass of snow per unit volume (kilograms per meter cubed). Typical densities of seasonal snow vary from 30 kg/m in dry, newly fallen snow to 600 kg/m in wet spring snow.

These results highlight the importance of prompt extrication by companions, especially in areas with a more maritime snow climate. Although the “survival phase” has commonly been described to be about 18 minutes long, our analysis shows that the first 10 minutes might be a more appropriate general guideline for Canada and other areas with a maritime snow climate.

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5. The study recommended that Airbags and Transceivers be used as they offered the best options to speed up rescue.

The use of avalanche airbags to prevent burial and avalanche transceivers to speed up the locations of buried avalanche victims are recommended. Both of these safety devices have been shown to reduce mortality significantly.

The study had numerous interesting facts about avalanche burials.

The two longest burials among survivors in the Canadian sample (120 and 300 minutes) both occurred in urban settings, whereas the maximum burial time among survivors in a remote setting was 55 minutes.

So?

When teaching at Colorado Mountain College in the Ski Area Operations program I tell my students the one thing we know about avalanches to an absolute certainty: Avalanches are made of snow.

For other articles on Avalanches see:

Mountain Magazine should apologize to the families who will soon lose loved ones because of its latest magazine.

Research shows beacons have issues with multivictim searches

Colorado Avalanche Information Center

It’s time to sign up to get the CAIC Avalanche Forecasts

Well written article about the risks of Avalanches and survival with the latest gear.

See this article by Earn Your Turns: Canadian Study reduces Avalanche Survival Time, http://www.earnyourturns.com/9079/avalanche-survival-time-reduced/

What do you think? Leave a comment.

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A new idea that makes sense in helmets: the Bern Hard Hat

Many people have heard my comments on helmets for the outdoor recreation industry. Very few helmets, if any, are fitted properly, worn properly or used properly. Many helmets are used in ways that increase the risk or are worthless because head injuries do not occur in the sport.

Examples are studies from Ski-Injury.com that showed helmets are only effective in skiing for slow injuries1,2 and that head injuries only represent 10-20% of all skiing injuries3 in one study and only 2 to 8% in another.4 For males between the ages of the late teens to their early thirties a helmet will not affect the mortality rate.5 Helmets do reduce head injuries.6 Several studies have shown the most important aspect of wearing a helmet on the slopes is to protect your head from being hit by a chairlift or lift if you fall down.7

The other argument with helmets is the issues of risk homeostasis or risk compensation. This theory states that the safer you feel, the more likely you are to increase your risk. Wearing a helmet will subsequently increase your risk of an accident because you feel safer with the helmet.8,9 Consequently injuries among skiers are highest among those that are wearing helmets.10

One place a helmet may make a difference is the courtroom. Judges and appellate courts invariably comment about whether the plaintiff in a lawsuit was wearing a helmet when the plaintiff suffered a head injury.

At the same time, helmets in some activities are needed. For skiing, if you recognize the possible risk homeostasis issues, buy a helmet that fits properly, properly wear the helmet and throw the helmet away if you have a major impact, they will prevent head injuries, not death, but injuries. Throw the helmet away? Yes!

Helmets come with disclaimers that say they should be discarded and destroyed if they suffer a major impact. This is because 99% of the helmets sold for most sports are sold with a plastic or other hard shell surrounding an EPS liner. The protection afforded by the helmet is combination of the shell and the liner. EPS is that hard foam under the soft padding that gives the helmet its protection. Because of the way the EPS and shell are molded together, cracks in the EPS are rarely visible from the inside. Moreover if there is a liner glued to the EPS. The EPS is difficult to remove from the shell and doing so ruins the helmet. Once a crack occurs in the EPS the structural integrity of the helmet is compromised and the helmet should be discarded.

Bern has come up with a slightly different approach to this problem. They have helmets, which they call Hard Hats that are lined with Brock foam.11 This foam is a multi-impact liner that allows the user to experience several if not dozens of impacts without having to replace the hard hat. Besides the foam is soft and very comfortable to wear, breathable and allows air to circulate as well as wicking.

The problem is the foam does not meet the current standards to receive ASTM or EN approval. So technically it is not a helmet but a hard hat. The buyer is faced with a decision to buy a helmet that does not provided the protection that an EPS lined helmet does or to buy a helmet that provides less protection, but more protection for the injuries helmets do really protect the wearer from. A real catch 22 for the buyer, but one worth studying. Bern offers all its helmets with Brock Foam with EPS if you like the style, but want different protection.

You can take a lot of falls. The choice is up to you, measured better protection at an minute amount for a small percentage of risk or a helmet that can take a beating, protect you head and last longer than one trip to the slopes.

1 Helmets on the slopes….Heads you win?

2 A summary of the research presented at the 16th International Symposium of the ISSS held in at Mount Arai, Japan in April 2005.

3 Helmets on the slopes….Heads you win?

4 BackTalk; Helmets Do Not Make The Ski Slopes Safer

5 Shealy research sheds light on helmet use

6 Helmet Safety, Standards and Design

7 Alpine Ski Injuries

8 Risk Compensation & Helmet Wearing. June 2001

9 Helmets

10 BackTalk; Helmets Do Not Make The Ski Slopes Safer

11 Bern Catalog

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A helmet manufacture understands the issues

Uvex has been selling ski and bicycle helmets for a while. Their helmets, from a legal standpoint, are about like everyone else’s. You can argue color, shape, design or air flow makes them standout, but the legal reality is Uvex helmets are a one-hit helmet just like everyone else’s. However Uvex has realized and have eliminated a flaw in their protection plan for customers. All helmet manufactures for the skiing, biking and other industries had missed a major component of head injuries.

Head injuries come in two different types, 1.) Bruises and cuts and 2.) Concussions. Most helmets do an adequate job of protecting against bruises and cuts to the head. At the same time, a plastic bowl and duct tape will also do a fairly good job for a lot less money. Concussions are the real threat to the long term health of participants.1

One of the major sources of concussions is blows to the jaw2. That is why football players and many other sports participants wear a helmet and a mouthguard.

Mouthguards protect three ways. Mouthguards protect against neck injuries, they protect teeth and they protect against concussions3. The protection against concussions is the most important thing a mouthguard does.4

At present The American Dental Association5 recommends wearing custom mouthguards for the following sports: acrobats, basketball, boxing, field Hockey, football, gymnastics, handball, ice hockey, lacrosse, martial arts, racquetball, roller hockey, rugby, shot putting, skateboarding, skiing, skydiving, soccer, squash, surfing, volleyball, water polo, weightlifting, wrestling.6 This list is old and has not kept with the increase in the variety of sports people are undertaking today.

Mouthguards take on an even bigger role in sports where the injuries to the head occur by hitting the jar or face such as skiing, biking and whitewater rafting.

Uvex has recognized this issue and is now selling an LP Mouthguard along with their ski and bike helmets. The mouthguard appears to be like those we used in junior high (way before middle school) football. It can be custom formed by boiling the mouthguard and then forming it to your teeth.

If you are serious about protecting yourself or your customers from injuries, then you need to understand the issues.

  1. What are the real types of injuries my customers face?
  2. What protections are available?
  3. What protections that are being used by the industry work?
  4. What protections being used by the industry don’t work?
  5. Why?

Based on the research from other sports, a person wanting to protect against head injuries should be wearing a helmet and a mouthguard. Thanks Uvex.

1 Journal of Athletic Training

2 For the Dental Patient

3 American Dental Association

4 Sportsguard Laboratories, Inc.

5 American Dental Association

6 Sports Dentistry

 

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