Debunking Hydrostatic Head

[David Olsen]

Dirty little secret.

Flame retardant specs can be met with a weak fabric that melts away from the open flame.

A 70d nylon type 6 with a .25 oz PU coating can meet specs.

A 30d nylon type 6,6 with a .25 oz sil coating will not.

Both will have similar HH, good enough for shedding water as a fly, mediocre for a floor.

The 70d will be heavier but with a lower tear strength.

[Matt Dirksen]

It was always my general understanding that retailers are not allowed to sell tents that don't pass CPAI-84 standards.(Of course like most things, this may vary from state to state as well.)

EDIT: I found this 5 year old document: http://www.outdoorindustry.org/pdf/ASTM_FAQ2007.pdf

But like anything, I'd be more worried about the toxicity of the retardant more than the tent burning up: http://cen.acs.org/articles/91/i19/Global-Ban-Flame-Retardant.html

Matt

[Roger Caffin]

The whole flame retardancy business is a classical example of politicians being led by the nose and business/bureacracy corruption.

There is only one company making flame retardants in the USA – guess who pushed for the legislation?

The single research paper 'supporting' the concept has been disowned by the author, who says that the company totally misrepresented his results.

The concentration of retardant required to get any useful results is far, far more than the legislation requires, so real fabrics which pass the test are no better than ones with none (and note Dave's comments).

The chemical used is toxic.

Me, I would actively work against the whole concept and oppose any attempts to enforce the idea. Yeah, I did research the whole subject at one stage. Phew.

Cheers

[Sam Farrington]

"I think you are setting up HH as a bit of a straw man for debunking."

We are so fortunate to have an editor who can cut through the bull in so few words.
Thank you, Roger.

[Sam Farrington]

Terra Nova has a 5 by 8 foot tarp in the 7 oz range that claims 3000mm HH. No claim of FR.
Around $100.

Golite has the same size at about the same weight, and claims FR and 1200 mm HH. Around $60.

What does this tell us? Not much, but leaning toward the T-N on the theory if you start at more than twice the HH, the result later will still be better. If you do your own HH testing, you can observe how rapidly the WP breaks down after the first drops, go back and retest to see what happens (it can be very different), keep the pressure on for a while, or retest again after putting the swatch through a washer cycle or two with no soap. Or you can fold the swatch and keep it compressed for a day or two, and then see what happens. Or you can experiment with sprays intended for the fabric's coating. By then, IMO, the HH readings will be more helpful. The military specs also require a min HH after the material has been put through specified rough treatment.

Note: The Prolite site gives the result of their own weighing of the product, which is helpful also.

[Roleigh Martin]

I’m curious how much it would cost to get hydrostatic head testing equipment and a consumer guide to such. I’m out in the wilderness long enough that if it was under $1,000 I could see getting it.  Any recommendations?  One or a couple of guys on this forum own such, right?  Your thoughts?  Thanks!

I’m interested because as the OP states, fabric degrades over time.  Joe Valesko at Zpacks said abouto Dyneema Composite Fabric (formerly Cuben Fiber) that (quote from an email he sent today to me): “DSM lists the HH on the .51 oz material as 15,000 mm. They list .74 as 20,000 mm. I don’t know why it is different since the membrane is the same.  1.0 oz is also listed as 20,000 mm.”

The Triplex Tent from Zpacks I have stayed waterproof in a puddle of 2 inches of water (which I woke up to 2 years ago) but this same tent, I swear, suffered floor leakage of water in a vicious 2 hour intense hail and rain storm this summer — I either had a leak in the floor or hydrostatic head failure.  I swore I saw water seeping through the tent floor.  I can’t say for absolute sure.  I tried to get Zpacks to (for a price) to replace my floor with their 1.34 oz sq yd CF but they won’t do custom stuff anymore, but he offered to use his standard floor material (1.0 oz sq yd CF) and after discussion, to sew it beneath (instead of replacing) the existing floor), so my “repaired” Triplex Tent will end up having somewhat the equivalent of 2 oz sq ft CF for next summer.  But I’d love to test each layer of the tent floor with a HH testing equipment.  I just don’t know how costly they are or who sells them.

[Ben H.]

You don’t need anywhere near a $1000 to test HH:

https://backpackinglight.com/forums/topic/44977/

You just need to be able to set up a column of water across a fabric sample.

ISO 811 is the appropriate standard, and it would be a good idea to get ahold of it if you attempt to make a tester.

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