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normal, flexible and free from obvious abnormalities,
while a deteriorated internal surface would be
completely invisible to a cursory external inspection.
It would be premature to speculate that this
deterioration is limited to braided hoses. Previously,
hoses comprised a rubber inner hose, a single
braid layer for reinforcement and finally a rubber
outer sealing layer. Today the rubber inner hose is
sometimes replaced with a polyurethane or nylon
hose (referred to as thermoplastic). The middle or
reinforcing layer is a polymer-filament braid, and the
outer layer is either a second braid — which has the
advantage of indicating when the inner hose has a leak
— or a polyurethane or synthetic-rubber sealing layer.
Newer second-stage hoses with a thermoplastic
inner layer may be vulnerable to degradation. This risk
does not apply to internal layers of synthetic rubber,
which appear to be impervious to this phenomenon.
DAN Research would normally wish to conduct
more in-depth analysis with a wider sample of
defective hoses, but because this is a potential hazard
to regulator function we prefer to err on the side of
caution and report this phenomenon now.
WHAT DOES DAN RECOMMEND?
DAN has contacted manufacturers of outer braided
hoses to assess possible causes and precautionary
measures, and we feel it is important to advise divers
as follows:
• All regulator hoses, including braided hoses, have a
limited service life regardless of external appearance
or reinforcement and protection provided by hose
protectors or the braiding itself. The failed hoses we
have seen are more than five years old.
• The internal section of newer hoses with a
thermoplastic inner layer appears to be uniquely
prone to polymorphic crystallization, especially in
hot, tropical locations. The phenomenon appears to
be a gradual process, but the disruption of gas flow
and regulator function is unpredictable and invisible
to external inspection.
• If there is any indication of gas-flow restriction,
particularly when using a newer hose, the diver
should immediately stop using the regulator. Perform
a careful inspection of the regulator and the hose. If
the regulator is not the cause, suspect the hose.
• Physically examine hoses by squeezing them every
inch or so to assess whether they exhibit the same
degree of flexibility. Any change in resistance while
squeezing along the length of the hose would be a
sign of a possible problem. This test is much easier
to perform with braided hoses than with harder,
outer rubberized hoses.
Following this advice, especially the recommendation
to regularly inspect hoses, will give you greater
confidence that your hoses will perform as they
should. Advocate for dive safety by promoting the
following ABC strategy:
• Air awareness: Make all divers aware of this problem
and the need for regular equipment servicing.
• Buddy breathing: Practice emergency air-sharing
procedures to ensure preparedness for and
appropriate action in the event of regulator failures
or out-of-gas situations.
• Customer choice: Ensure that any hose purchased
displays on the ends information about the
manufacturer, the production date and the standard
used. Check that this information is consistent with
that on the packaging. AD
We ask all divers who observe this inner-
hose degradation to please email DAN at
, preferably providing
pictures that show the condition of the hose.
This will enable us to capture as much
information as possible so we can learn
more about this phenomenon. We will share
any new findings, cautions and advice with
the diving community.
From left: Degradation is
a slow process, invisible
until there is a total failure
(top). This open hose shows
the extent of degradation
(bottom). This hose
interior is not affected by
polymorphic crystallization.
Replace old hoses, limit
hoses’ exposure to high
temperatures, and follow
manufacturers’ maintenance
recommendations.
References
1. Vann R, Lang M. Recreational diving fatalities. Undersea Hyperb Med 2011; 38(4): 257-60.
2. Davis A. Nylon-braided regulator hose diving emergency. Scuba Tech Philippines. July 22,
2015.
Crystallization. Accessed December 7, 2016.
3. Douaire M, di Bari V, Norton JE, Sullo A, Lillford P, Norton IT. Fat crystallisation at oil-water
interfaces. Adv Colloid Interface Sci 2014; 203: 1-10.
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JAVIER POLANCO
SHERYL SHEA
SHERYL SHEA STEPHEN FRINK