Your Underestimated Life-Line…… - Breathe Safety · Breathing air hoses are probably the...
Transcript of Your Underestimated Life-Line…… - Breathe Safety · Breathing air hoses are probably the...
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Copyright © Breathe Safety Ltd 2017
Your Underestimated Life-Line……
The Importance of Breathing Air Hose or Compressed Air Supply Tube (CAST)
Construction, Assembly, Inspection and Working
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Copyright © Breathe Safety Ltd 2017
Contents
Introduction
Investigating incidents with breathing apparatus failure.
EN Standards for breathing hose and CE Marking
Critical elements in a breathing hose construction
Typical Failures in Manufacturing
Where breathing air hoses fail in use
How to avoid failure of breathing air hose
Summary – what are the loses?
Further Information
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Copyright © Breathe Safety Ltd 2017
Introduction
Breathing air hoses are probably the simplest component in any airline breathing apparatus
system, yet they are one of the most under-rated in terms of importance. When you don an
airline breathing apparatus set, a long duration supply of compressed air feeds you either
from a compressor or high-pressure cylinder bank, the functionality of the whole system
depends on the integrity of the airline that connects the wearer’s breathing apparatus to the
compressed air source, and yet it is the most neglected part of the system in terms of
manufacturing quality control, and ongoing maintenance. Airline breathing apparatus sets
are checked meticulously, cylinders are tested, compressors are serviced and air quality
tested, but what about the humble airline that everyone expects to just ‘work’, and yet the
statistics show that more than half the serious failure incidents with airline systems are with
the airline!
Compressor / Cylinders Breathing Airline Airline set
In advanced breathing air systems and diving applications the air supply hose is not
surprisingly called the ‘umbilical’, bringing the essentials for maintaining life in the most
hazardous of environments, it remains one of the most critical parts of the system.
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Investigating incidents with breathing apparatus failure.
Any incident involving breathing air hose is generally high profile in terms of safety, because
typically they are used in atmospheres which are not respirable or I.D.L.H. (Immediately
Dangerous to Life and Health) There has been many incidents, which as a hirer we have
had to investigate with hire fleet hose failures. Establishing the root cause of failure has
always been the emphasis of our investigation, and learning how we as a manufacturer and
hirer of breathing air hose can improve the following in view of there being no repeat
incidents:
• Our hose, couplings, and specification of the product
• Our processes in hire and manufacturing inspection
• The client’s working processes
The successful strategy of refining the cause of failure, means that repeat incidents have
been almost eliminated.
EN Standards for breathing hose and CE Marking
The standards which cover breathing hose are EN14593 and EN14594, and these cover not
only the hose but the integrity and type of coupling. Some of the type approval tests are
quite challenging to pass. Tests cover tensile (pull) testing to 1000 Newtons, kink resistance,
crush resistance, flexibility, heat resistance and antistatic properties. The hose should
generate no significantly noticeable odour, and be resistant to the environment in which it is
used. It should withstand over pressure of up to 30 bar.
The standards state that couplings should not be affected by hose twisting, with at least one
swivelling coupling fitted adjacent to the wearer. The couplings should be designed such that
they prevent unintentional interruption of the air supply, typically this means that they require
at least 2 intentional actions to un-couple.
Hoses should be marked with appropriate standard conformity and any special conformity
such as antistatic.
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Critical elements in a breathing hose construction
A breathing air hose is not a lot different to other compressed air hoses, other than the
requirements of the standards. The construction is the same typically with an inner layer,
outer layer, and braided reinforcement in between. Materials used will depend on the
application but typically are PVC, nitrile rubber or Polyurethane.
Hose terminations are critical – quick release couplings must comply with the EN standard
which requires 2 deliberate actions to uncouple. Major manufacturers who have breathing air
specific couplings are CEJN, Rectus and Stabil. The greases used in these couplings are
also breathing air safe.
Hose terminations will be made from nickel plated brass, brass, or stainless. Corrosion is
minimised with these materials. Stainless is preferable as its corrosion resistance is better
and the material is harder and tougher. Brass although acceptable will tend to crack if its
thickness is inadequate.
Apart from the quick release couplings themselves, the success of a hose termination
consists of 3 elements, very much like the fire triangle, if one is removed then it will result in
failure of the hose assembly:
Hose
Hose tail Ferule
Outer layer
Braided reinforcement
Inner layer
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Typical Failures in Manufacturing
The following shows typical hose damage/ failure and its cause:
• Hose bore restricted by overcrimping, or improper hosetail/ ferule specification,
where hose ferule is longer than the tail.
• Hosetail pulls out easily – improper hosetail/ferule specification
• Hosetail specification and design inadequate – hose retention will be affected by
number of barbs , length of tail, and barb shape.
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• Ferule design -length, material, how much it is swaged.
• Hose tail fitting cracked either through overtightening or impact in use
• This cross section shows where the hose is not pushed up tightly to the end of the
ferule. Although not serious in this case it can be pushed off further and inadequate
barbs on the hose tail grip the hose.
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Where breathing air hoses fail in use
The environments where breathing apparatus is used are typically harsh, and the brunt of
this is taken by the hose. The airline set is on the wearer and who usually has respect to his
safety, the air source is outside the work environment, but the hose is dragged, dropped,
and snagged in the worst conditions, and exposed to the worst chemicals and
contamination. In some ways, the failures are no surprise. The following are typical failures
in use:
• Steam or hot pipework damage to hose – weakening its wall
• Hose tail pulls out of hose – hose tail inadequate, or ferule not correctly swaged on to
the hose
• Coupling comes apart – dirt ingress prevents swivelling of male and female
couplings, and unscrews the female coupling itself, or can unscrew the coupling from
the hose tail.
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• Hose rupture caused by hose tail digging into hose and creating weakness when
sharply bent.
How to avoid failure of breathing air hose
1. Ensure the hose is approved
Hoses must be either CE of NIOSH Approved, and should be marked accordingly.
2. Ensure the hose is correctly specified for the environment it will be used in.
There are many hoses that will meet the requirements of breathing air standards, that
will not necessarily hold up to the work environment they are used in. light duty will
fail in heavy industrial environments, while other seemingly adequate hoses may not
offer proper chemical resistance.
3. Ensure the hose is assembled by a company who:
• Batch tests their assembled hoses at a suitable regularity.
• Has proper hose assembly design and validation before product launch
• Has assembly quality control in place.
• Inspects and tests hoses adequately before supply or hire.
4. Ensure the hose is inspected in line with manufacturer’s requirements
5. Ensure the hose is inspected before and after use, bearing in mind the severity of the
usage. Maintenance is critical – no hose will last forever. Some hoses are used for 5
years and look like new – others will barely last for weeks in very harsh environment.
Inspection and testing needs to be appropriate for the application.
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Summary – what are the loses?
The ultimate price of breathing air hose failure is loss of life.
Although less serious, but still very disruptive, any incident creates other losses. Crews of
workers are stood down while incidents are investigated, machinery lies idle, and work is
delayed. One such case where we investigated an airline incident, it cost a tank cleaning
contractor with 10 operatives and associated machinery over £6000.00 per day!
Learning from the past is key in ensuring that there are no incidents and an airline BA user
can go to work confident that his hose will not fail.
Report Prepared by Nick Aris, Breathe Safety Ltd, 6 June 2017
Further Information
Breathe Safety and its sister company, Luno Systems, specialise in the manufacture of airline breathing
apparatus, and have a range of equipment for hire and sale. Other support services offered are consultancy,
product development, training, and equipment servicing. Having the ability to manufacture equipment compliant
to CE and NIOSH Regulations, and conduct type approval testing in our ISO17025 UKAS Accredited laboratory
means we can offer a full support service to any client in this sector of safety.
This whitepaper is copyright © Breathe Safety 2017. No part of this document may be
copied without prior consent from Breathe Safety Ltd