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Swan-Necks & Pigtails - The use
of swan-necks (a "U" shaped pipework bend,
see, Fig.1) and pigtails (a "spiral " shaped
bend, see Fig.2) in hot and cold water systems is often
subject to much debate. Legionella Control Internationals
stance on the issue is that they should not be used
in hot and cold water systems as they have the potential
to increase the risks associated with Legionella. However,
recently one of our large healthcare clients asked us
to clarify our position so we turned to leading Legionella
specialist Dr. Tom Makin for expert comment.
Dr. Makin is co-author of the Department of Health’s
“Health Technical Memorandum” HTM 04-01
dealing with Legionella control in healthcare premises;
and co-author of the Health & Safety Executives
“Approved Code of Practice and Guidance”
for the control of Legionella bacteria in water systems
(L8).
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Fig.1 - Swan-neck
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Fig.2 - Pigtail
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Expert Comment
""... Swan-necks and pigtails are not
considered to be a significant source of legionellae
if the system water temperature is always maintained
at 60oC. Problems arise when this temperature
is not achieved and it falls below 50oC,
the lower thermal death point for Legionella.
Many argue that swan-necks and pigtails should
not be regarded as a significant source of legionellae
because they are usually considerably shorter than the
2m length allowed in HTM04-01 for pipe connections to
hot and cold water outlets.
| "Dead-legs
of any length represent a risk if the water temperature
is conducive to microbial growth ..." |
Deadlegs
Dead-legs of any length represent a risk if the
water temperature is conducive to microbial growth.
The 2m length quoted in HTM04 refers to the maximum
permissible length of a deadleg in blended hot and cold
water outlets. Clearly, there is no option but to have
a small section of pipe from blended hot and cold water
supplies to the outlet. The length of this section of
pipe can vary and may be very short e.g. where the thermostatic
mixing valve is incorporated as an integral part of
the blended outlet; however it should not exceed 2m
in length. The risk in such situations is mitigated
because at some point these sections of pipe should
have water flowing through them; and at least twice
weekly in healthcare premises, if compliant with HTM04-01.
The regular use of outlets helps prevent the proliferation
and accumulation of legionellae both in the outlet and
associated sections of pipe.
Swan-necks and pigtails
In most cases there is no flow of water through
swan-necks and pigtails, therefore there is no opportunity
to discharge and dilute any accumulating biofilm. One
option to reduce Legionella related risks in these devices
is to fit valves that would allow them to be flushed
to waste at a suitable frequency. However, this additional
responsibility is often unpopular with users, particularly
if there are alternative systems available that do not
require flushing. I understand there are suitable alternatives
to pigtails and swan-necks in which the volume of retained
water is considerably reduced.
It has been suggested that the material from which swan-necks
and pigtails are constructed (copper or brass) is sufficiently
antibacterial to prevent the accumulation of biofilm
within the device. It is recognised that heavy metals,
particularly copper and probably also brass (although
I have seen no peer reviewed evidence confirming the
efficacy of the latter in controlling biofilm), have
antibacterial properties and so can delay the accretion
of biofilm. However, passivity eventually occurs due
to a fine coating of inorganic deposits and scale build-up
on the internal surface, which can afford protection
to microorganisms that alight on the surface, so enabling
them to form into biofilm. Over time, even copper and
probably brass surfaces will support biofilm, particularly
if exposed to warm and stagnant water as indeed many
pigtails and swan necks are.
Recent study
A recent study carried out by Dr Mathys and colleagues
from Munster University, Germany, showed that plumbing
systems with copper pipes were more frequently contaminated
than those made of synthetic materials or galvanized
steel. Other studies have shown copper to be better
than plastics and other materials at resisting the development
of microbial colonisation in aquatic systems. Perhaps
certain types of copper are more susceptible to accretion
of biofilm than others, but all at some point will succumb
to microbial colonisation.
Conclusion
In each case, where swan-necks and pigtails have
been installed it will be necessary to assess the risk
of Legionella proliferation in those devices. If a Legionella
risk is shown to exist, then it should be controlled,
where it is reasonably practicable to do so. Both manufacturers
and installers of these devices have responsibilities,
as highlighted in the HSE’s Approved Code of Practice
and Guidance (L8), with regard to helping to control
the risk of Legionella infection linked to such devices
".
References
Werner Mathys, et al. 2008. International
Journal of Hygiene and Environmental Health. Volume
211, issue 1-2, pages 179-185. Occurrence of Legionella
in hot water systems of single-family residences in
suburbs of two German cities with special reference
to solar and district heating.
Additional Information
For further information and expert assistance please
call us on +44 (0) 161 877
0586 or email info@legionellacontrol.com.
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