Fan packs vs canister...the pressure issue ??

[wstdeep]

A recent conversation has me pondering the following: In cases of a wearer submerged/engulfed in heavy and or wet snow before pulling the handle will a fan style bag have enough power to inflate the airbag when weight is compressed on it. In other words can fan power generate the enough pressure to inflate while a pack is under pressure from exterior sources to a level comparable to a 3000psi canister setup ? Of course the compression would change as one flows and tumbles in the stream of moving snow but wetter snow would still have less air available for the fan to compress.

It seems like a stretch but has anyone had a real world experience or done specific testing on this issue ?

[nickinbc]

The canister might have a high pressure, but it actually fills the airbag largely by drawing in external air through a venturi. So I think the difference is going to be a lot less than you might think.

The canister alone doesn't have enough gas to fully inflate the airbag. For example the BCA canister has a volume of 0.29 liters at a pressure of 2700 psi. Since pressure x volume is constant that would expand to 52 liters at atmospheric pressure (15 psi). The BCA airbag has a volume of 150 litres so the canister on its own would only 1/3 inflate it.

[TGReek]

Wouldn't it be a moot point at that stage of being caught in an avalanche? I could see if you had just been submerged and were still moving with the slide that inflating the bag could give you a shot to get back/near to the surface. However if you had already stopped moving, then inflating your bag won't help you at all since the whole point of it is to keep you near the surface. If anything, couldn't inflating your bag compress your already limited space under the snow? I feel like I would recommend against inflating once buried and no longer moving.

[wstdeep]

"Of course the compression would change as one flows and tumbles in the stream of moving snow but wetter snow would still have less air available for the fan to compress."

Clearly referring to being in moving snow...obviously no point in pulling if your already entombed in static snow.

[Scottish_Skier]

In cases of a wearer submerged/engulfed in heavy and or wet snow

Then there is no way your hand would be able to activate trigger.

[TGReek]

Clearly referring to being in moving snow...obviously no point in pulling if your already entombed in static snow.

Sorry, misunderstood the question. Found two pieces of information. First is an article from BCA that seems to say a buried sledder was able to deploy his airbag once he had stopped moving. Not entirely clear how this all went down though. https://backcountryaccess.com/deploy...uried-sledder/

Second is an outside article. If you go down to the bottom it has the following paragraph: "Critics say that trying to inflate the fan when there’s pressure on the bag won’t work. Black Diamond disagrees. According to the company, even though the fan-powered system lacks the initial explosive power of a canister system, it can quickly overcome any outside pressure once the balloon has some air in it. “If the system is initially hindered, which can happen to cylinder systems too, repeated fan bursts will correct the problem,” said Nathan Kuder, Black Diamond’s softgoods category manager. In lab tests, JetForce technology repeatedly lifted 250 pounds when inflated."

So question is, would the bag being able to lift 250 lbs be enough while you're under moving wet/heavy snow? https://www.outsideonline.com/192222...cons-avy-packs

[summit]

nickinbc nailed it

to TGReek's points, it is important to remember that bags don't work on buoyancy, but rather vertical partical size sorting during turbulent flow. It is important to remember that in turbulent flow the pressure on the bag will not be constant/continuous thus it may have an opportunity to fill during brief low pressure or filling into voids while valving prevents pressure from expelling the air.

In theory, fan bags do offer the advantage of being able to deflate after a delay creating an airspace for someone who is not sorted to the top of the slide, good if it hit from above in a valley/terrain trap.

It is doubtful either system generates sufficient pressure to displace static debris. If you want to test, maybe try pushing deploying your fan bag while someone else gives it a hug to prevent inflation. Report back!

[TGReek]

If you want to test, maybe try pushing deploying your fan bag while someone else gives it a hug to prevent inflation. Report back!

BD says that their battery-powered packs can lift 250 pounds. What do we think this correlates to in terms of ability to move snow in an avy?

[PNWbrit]

BD says that their battery-powered packs can lift 250 pounds. What do we think this correlates to in terms of ability to move snow in an avy?

pretty meaningless.

[Toddball]

It is doubtful either system generates sufficient pressure to displace static debris.

Sounds like such pressure could squash the wearer before displacing much snow, anyway.

Another test: fan pack on, friend on shoulders, pull trigger, ????