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Develop - what's new from the Alpkit Design Team

Bivvy Bag development

By Nick
17, May, 2016

Development for our new Alpkit hooped bivvy hit a problem when the new super-light, breathable fabric we were using turned out to be not breathable enough...

Most outdoor gear testing isn’t really dangerous, Graham Thompson doesn’t risk life and limb every time he ventures out on the Lake district fells to test the latest waterproof, Chipps doesn’t emulate Danny McAskills ridge ride on every Calderdale trail, and the Alpkit Product crew don’t regularly hang out on Denali tent testing (although we wish we did).  

However, some products are genuinely safety critical so need to be tested and its inconceivable today that some products wouldn’t have a barrage of tests put against them,sleeping bags, carabiners helmets to name but a few.

The humble bivvy bag isn't an item that immediately comes to mind as overtly dangerous but bivvy bags and tents can hide a dark and potentially lethal secret; CO2.

I often get asked at shows about the Hunka “why does it have drawcord” of which my standard answer is “because otherwise you will DIE, my friend” in my best hammer house of horror style.
The problem with bivvys is that they use “breathable” fabric, which as we should know doesn’t mean you can breathe through it, but many don't. So on the most part designers ensure most bivvys can’t be 100% sealed up by closure design or venting.

WL Gore came out with an air permeable waterproof fabric and I think I was one of the first civilian users of this product and certainly one of the first designers to get Exchange Lite fabric in to bivvys and single skin tents. So I was genuinely excited when one of our high tech fabric suppliers showed us air permeable PU fabric there was a chance that we could produce a single skin, fully sealable hooped bivvy bag that weighed 500g for well under £100...

It looked brilliant, packsize was good and weight was perfect...

It looked like we had a dream product...

Do you know how long that dream lasted?

4 mins.

Four minutes until the build up of C02 was a level likely to cause death... that isn't ideal...

Joking aside, that is genuinely dangerous, that's not an angry email about being cold in a snow hole in Norway,  that's a "I wonder how Neil got on with that bivvy, I haven’t heard from him lately"... Neil could officially be the most hardcore outdoor equipment tester.

Neil Cottam is our intrepid biker and adventurer and he knows a thing about enclosed spaces and dangerous gases.

So armed with Crowcon Gasman and full bivvy test support crew. (his mate Mitch) he offered to test the development sample Hooped Bivi we'd made...

Below is the Tech stuff: 

CO2 saturation 
  CO2 Affect on you
250-350ppm (0.025 - 0.035%) Normal background concentration in outdoor ambient air
350-1,000ppm Concentrations typical of occupied indoor spaces with good air exchange
1,000-2,000ppm Complaints of drowsiness and poor air.
2,000-5,000 ppm Headaches, sleepiness and stagnant, stale, stuffy air. Poor concentration, loss of attention, increased heart rate and slight nausea may also be present.
5,000 Workplace exposure limit (as 8-hour TWA) in most jurisdictions.
>40,000 ppm Exposure may lead to serious oxygen deprivation resulting in permanent brain damage, coma, even death.









Test results:

(There was a light wind during the testing which will bolster circulation. Under still conditions these readings may have been higher).

The Crowcon Gasman device that we used measured in percentages, these percentages expressed at PPM  is % x 10000. IE 0.15% = 1500ppm. 0.5% = 5000ppm


With the access fully open the readings were the same as open air. Zero or very close to zero.

With the door fully open and the mosquito panel fully zipped the readings averaged 0.12 - 0.15% 1200-1500ppm. This is fine.

With the door fully zipped up: 1min 45s to reach 0.5% 5000ppm and approximately 4mins to reach 1.0% 10000ppm. This is bad, very, very bad... 

With mosquito panel fully zipped and the door partially open at the top the readings maintained an average around 0.25% 2500ppm. This is acceptable.

However with the door partially open to the side (slashed bottom to top) the readings were much lower: 0.2% - 2000ppm on average.

This seems to allow the heavier CO2 to escape and allows fresh air to circulate more freely. Much Better.


So, thanks to Neil (and Mitch) we've learnt a lot and can use the results to tweak the design and make this great product even better.... watch this space for future developments...

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