Waterline - The Journal of the Water Management Society - Winter 2006

Waterline – The Journal of the Water Management Society – Winter 2006

                The Principal Types of Mixer-Valve Showers and
               Reducing Risks Associated with Legionella Bacteria
                                          David T. Lloyd Jones
                  Founder of the Legionella control procedure described in L8 - paragraph 166,
                   and self-purging showers described in HTM 04-01, Part B - paragraph 7.88
                                           Aqua Hygiene Products

In October 2006, the Department of Health described the importance of noting the distinction
between the principal types of showers in their Health Technical Memorandum (04-01) for Water
Services(1). Part B (paragraph 7.88) of this document describes: “It is important to note the
distinction between self-purging and self-draining showers. Self-purging showers can be an
effective Legionella control procedure, while self-draining showers can support the proliferation of
Legionella”.

This paper gives practical advice relating to the principal types of showering systems (of the
manual mixer valve type) and associated guidance, issued by the Health and Safety Commission,
and Executive; described in the Approved Code of Practice and Guidance – Legionnaires’
disease (L8)(2). The guidance described in L8 illustrates good practice and when followed you will
normally be doing enough to comply with the law in respect of those specific matters on which the
code gives advice.

Although cooling towers are incriminated in large outbreaks of Legionnaires’ disease (LD) it is
domestic water services that are linked with the majority of reported cases. Inhalation of
contaminated aerosols created by showers is widely-believed to be the single-largest source of
legionella infections. Conventional showers are promoted with healthy life-styles images,
however, when underused a reasonably foreseeable potential risk to health exists from legionella
proliferation and exposure. The wiser and wider use of advocated legionella controls are
necessary to reduce the widespread risks to health from conventional showers, which are
described in L8. Aqua Hygiene Products has carried out intensive scientific research for a better
understanding of legionella dynamics in the peripheral parts of domestic water systems, leading
to the successful development of safer and sustainable showering methods: Self-purging
showers; L8 and HTM 04-01 describe the findings of this research.

Nowadays, the risks from this primarily man-made disease implicates a far-wider perspective, not
only is our social responsibility of providing safer and sustainable environments under scrutiny,
the risks from brand impact to businesses and the implications of personal legal liability, including
corporate manslaughter charges, have emerged in recent times. As such, there is increasing
pressure on designers and operators of domestic water systems to justify their legionella control
strategies and practices, in line with Health and Safety Law and H.M. Government Design and
Procurement Briefings.

Legionellae in the environment
Legionellae will survive at temperatures below 20°C but are unlikely to multiply. As temperature
rises above 50°C legionellae are less able to survive, and at 60°C the majority will be killed within
5 minutes. Maintaining water temperatures below 20°C and above 50°C is therefore the main
method of controlling legionellae in domestic water systems as recommended by the DoH and
HSE. It was recommended that calorifiers in a recirculating hot water system should distribute hot
water at 60°C and receive the return hot water supply at not less than 50°C. This will eliminate
most legionellae in the recirculating water. However, those legionellae that enter the warm
stagnant water trapped between the recirculating supplies and outlets, after surviving a calorifier
when the water temperature has fallen (e.g. at peak demand), or by evading the effect of high
temperature inside amoebae, are likely to proliferate. The inability of a hot water regime to
eradicate legionellae from a model domestic water system has been described by others(3).

A reasonably foreseeable potential risk to health
Primarily, LD is a man-made disease and infections caused by the built-environment are
avoidable. However, legionella infections continue to be reported due to compromises taken in
the design and operation of shower facilities; statements released further to fatalities have also
referred to cases attributed to an extremely rare set of circumstances. However, it is well-
documented that conventional showers provide near-ideal conditions for legionella amplification
and exposure. Legionella has been shown to thrive in the warm stagnant water found in
showerheads and deadlegs, where there is a plentiful supply of nutrients found in materials and
biofilms (a thin slime like film with entrained debris) lining the internal aspects of pipework and
fittings. In a few days non-use of showers, legionellae has been shown to proliferate to levels that
are potentially harmful to health. When next used, those showering are exposed to significant
amounts of aerosols (fine mists of water droplets) which carry legionellae, and when inhaled the
potentially fatal LD primary-route of infection is complete; it is therefore prudent to consider ways
of breaking this infection route.

Risk assessments should identify the actions required for when conventional showers are
underused. Assuming continuous regular-use of conventional showers has been shown to be
unreliable legionella control strategy, and it is widely-accepted that showers are expected to fall
out of use during their life-cycle, due to foreseen or unforeseen circumstances, e.g.:
commissioning, holidays, refurbishments, absenteeism, location – those showers in groups that
are conveniently positioned are used more frequently, often leaving others little-used, etc.

Studies of legionella control in peripheral parts of domestic water systems have shown how the
designs of pipework and fittings must interrelate with water pressures and flow rates for efficacy.
Careful consideration should be given to the water flow shearing effect on unstable contaminated
biofilms and how these are carried from the system when flushing. To achieve safer showering
systems, the design and construction of all parts of the shower system should be considered; the
following are often overlooked:

    •    Flexible shower hoses, post flushing - it has been shown that contaminated biofilms
         lining the internals aspects of hoses can be dislodged due to physical movements whilst
         in use, creating an exposure to legionellae;
    •    Shower hoses allow showerhead contact with users and used bathwater, an
         underestimated risk to health from legionella infections amongst other infections;
    •    Avoid horizontal deadleg pipework, which encourages the entrainment of debris etc.,
         when practical;
    •    Avoid multiple showers supplied by single mixer valves (L8, 152. h);
    •    Positioning conventional mixer valves too close to hot water supplies has been shown to
         significantly increase legionellae growth in these devices - avoid optimum stagnant water
         temperatures for legionellae proliferation;
    •    Legionella control efficacy – caution should be exercised when operating showers below
         0.5 bar water pressure;
    •    Sprayplates – where multiple spray pattern devices are fitted, regularly flush through all
         spray patterns to reduce biofilm build.

Water conservation guidelines may recommend the use of low flow rate outlets. However,
                                                               (4)
scientific studies describe the potential risks of these devices . When considering low flow rate
outlets, or reduced volume flow outlets, it would be prudent to seek supporting legionella control
information from suppliers (L8, 70.b).

Advocated legionella control procedures, described in L8

Removal of underused showers - Paragraph 164
“Before carrying out the following procedures consideration should be given to removing
infrequently used outlets. If they are removed the supply redundant pipework should be cut back
as close as possible to the common supply pipe, for example to the recirculating pipework or to
the pipework supplying a more frequently used upstream fitting”.

This procedure breaks the infection route with regards to legionellae exposure from individual
showers. However, removal can create a blind-end of pipework that should ideally be cut back
short enough to maintain the water temperature in the connected common pipe. It has been
shown that blind-ends can trap particulates that encourage biofilm development and over several
seasons this may create areas for legionellae to evade the effects of raised hot water
temperatures and secondary water treatments. Blind-ends physically prevent the passage of
legionellae, and over several seasons it has been shown that luxuriant growth (overgrowth) of
legionellae colonies can occur, which may “seed” connected water supplies with legionellae. It is
therefore good practice to remove blind-ends wherever possible.

Self-purging showers - Paragraph 166
“Where it is difficult to carry out regular weekly flushing, the stagnant and potentially
contaminated water from within the shower/tap and associated deadleg needs to be purged to
drain before the appliance is used. It is important that this procedure is carried out with the
minimum production of aerosols, e.g. additional piping may be used to purge contaminated water
to drain”.

This is the legionella control procedure founded by Aqua Hygiene Products for Safepurge self-
purging showers; a practical control method, achieved through sustainable means. Self-purging
showers avoids the need for regular weekly flushing and hence avoids subsequent flushing
lapses. Designated weekly-flushing personnel are no longer required and hence the associated
risks to health from carrying out this task are eliminated. The self-purging procedure offers
environmental benefits by avoiding the unnecessary waste of significant amounts of power and
water associated with regular flushing.

Self-purging shower installation

The schematic diagram shows a typical Safepurge™ self-purging shower installation. The
showerhead (4) is connected to common hot and cold water supplies (1) via deadlegs (2), and is
controlled by a suitable mixer valve (3). The purge-pipe (5) connects the showerhead to the
waste water pipework (7), via a Type A air-gap arrangement (6), which is developed to avoid the
production of aerosols and prevent foul smells / aerosols drifting from the waste pipe.

Installation is practical where waste water pipework is exposed in service voids etc. that allows for
direct connection of the purge pipework. In older buildings this may be more difficult to achieve
and connections are often made beneath wash hand basins.

Operation
When not in use, the Safepurge sprayplate physically protrudes from the showerhead to kill
legionellae and prevent biofilm development by desiccation.

To operate, set the mixer valve to a warm/hot temperature. The unwanted cooler and
contaminated stagnant water from deadlegs and fittings is purged safely through the showerhead
and purge pipework to a connected waste water pipe; immediately before use and without the
production of aerosols. The time taken for the purge-cycle to dispose of this unwanted water is
determined by the installation layout and hydraulic characteristics of the water system; typically, it
takes between ten - twenty seconds for the mixed water temperature to reach the actuating
temperature of the thermal purge-cycle controller that closes off the purge water flow.

The showerhead now re-directs the water flow to the sprayplate, which is automatically drawn
back into the showerhead; featured in the HSE’s training videos. A showering spray pattern is
delivered and hot and cold water showering water temperatures are now maintained as normal.

After showering, turn off in the usual manner. The Safepurge sprayplate automatically protrudes
from the showerhead to continue the legionella control process.

Regularly flushing conventional showers - Paragraph 165
“The risk from legionella growing in peripheral parts of the domestic water system such as
deadlegs of the recirculating hot water system may be minimized by regular use of these outlets.
When outlets are not in regular use, weekly flushing of these devices for several minutes can
significantly reduce the number of legionella at the outlet. Once started this procedure has to be
sustained and logged as lapses can result in a critical increase in legionella at the outlet. Risk
assessment may indicate the need for more frequent flushing where there is a more susceptible
population present, e.g. in hospitals, nursing homes etc”.

Paragraph 166 of L8 also describes “where it is difficult to carry out regular flushing”, which
highlights how onerous this manual task can be. Subsequent flushing lapses have shown critical
increases in legionellae in showerheads that has resulted in fatalities.

HTM 04-01, Part A, describes that conventional showers should be flushed at least twice weekly.

Flushing process
Designated flushers set shower mixer valves to a warm/hot setting. Flushed water carries water
borne legionellae and shears off unstable contaminated biofilms lining pipework and fittings. For
control efficacy, this contamination must pass all internal restrictions (complex sprayplates etc.)
and exit the shower installation. Longer flushing periods are required to overcome the effects of
poorly designed fittings and sprayplates; a primary reason why conventional showers are flushed
for several minutes.

The environmental implications of regular weekly flushing falls under increasing scrutiny as
significant amounts of power and water are wasted, which is unacceptable to those organisations
wishing to demonstrate environmentally friendly practices.

Record keeping and flushing personnel
To help avoid subsequent lapses in flushing showers, L8 describes a recording procedure;
essential for organistions to demonstrate due-diligence. L8 describes how personnel designated
to carry out legionella control duties, including those who flush showers, should be trained for
their tasks; the flushing task must not be added to cleaning or other general duties.

Further to a hospital related showering fatality, a public inquiry(5) published recommendations for
those staff that should be excluded from flushing procedures: staff with cancer, diabetes, chronic
lung or kidney disease, immunosuppression (especially that caused by steroid therapy), staff who
have had an organ transplant, smokers and alcoholics.

Appendix 1. Checklist 2: Hot and cold water services
Conventional showerheads are often associated with the highest numbers of legionellae in
domestic water systems. This checklist describes how conventional showerheads and hoses
should be dismantled, cleaned and descaled quarterly or as necessary.

HTM Part B, Paragraph 7.87, describes the hyper-chlorination of showerheads and angle valve
strainers has only a short-lived effect on legionella. Manual cleaning to remove scale and other
deposits should be carried out at least quarterly, and more frequently if required.

There have been recent shower related fatalities associated with conventional showerheads
cleaned at six monthly intervals; it should be remembered that contaminated biofilms have been
shown to develop on conventional sprayplates within weeks. It would therefore be prudent to
consider more frequent cleaning; especially those showers in high-use that can trap increased
amounts of debris.

Self-purging showers virtually eliminates this cleaning requirement; the patented self-cleaning
sprayplate kills trapped legionellae and prevents biofilm development, daily, and naturally by
desiccation.

Automatic drain valves (ADV’s) are not recommended - Paragraph 167
These devices enable water to be drained from the showerhead, hose, and mixer valve after use.
Studies have confirmed that ADV’s were ineffective against legionellae colonizing showers(7). L8
describes how these devices, also known as self-draining showers, are not recommended as a
method for controlling the risk of exposure to legionella, however, they continue to be installed
worldwide.

The Department of Health, Water Services Health Technical Memorandum: 04-01, Part B
describes “It is important to note the distinction between self-purging and self-draining showers.
Self-purging showers can be an effective legionella control procedure, while self-draining showers
can support the proliferation of legionella”.

A better understanding
People may have paid the ultimate price for mistakes made with ADV’s/self-draining showers,
however, lessons learned from this emphasis a primary rule of research: A scientific breakthrough
can only be realised through the fullness of time, without which, whilst it may at first appear to
offset one problem but only later is it realised that it can exaggerate another. As new products
enter the market place it would be prudent to remember this rule and seek assurances from
independent experts who have carried out relevant performance related studies over several
seasons.

It should always be remembered that legionella infections caused by the built-environment are
avoidable and as legionellae have a proven track record in adapting to new environments, it
would be prudent to remain vigilant for developing resistance to whichever control mechanism is
applied, and to never underestimate the value of practical engineering solutions such as self-
purging showers.

Further information
Technical due-diligence guide, email: guide@safepurge.co.uk
www.safepurge.co.uk

References
1. Department of Health. 2006. Health Technical Memorandum 04-01: The control of Legionella, hygiene, “safe” hot
water, cold water and drinking water systems – Part B: Operational management

2. The Health and Safety Commission. 2000. Legionnaires’ disease, the control of legionella bacteria in water systems,
Approved Code of Practice and Guidance (L8).

3. Pavey, N.L. 1996. Ionisation water treatment for hot and cold water services. BSRIA Technical Note TN 6/96.

4. Halabi M., et al. 2001. Non-touch fittings in hospitals: a possible source of Pseudomonas aeruginosa and Legionella
spp; Journal of Hospital Infection, 49:117-121.

5. South Eastern Health Board. 2003. Independently Chaired report on Legionellosis at Waterford Regional Hospital.

6. Makin, T. 1998. Control of legionellae in domestic water systems, International Symposium on legionella. Institute of
Healthcare Engineering & Estate Management.

7. Makin, T. and Hart, C.A. 1990. The efficacy of control measures for eradicating legionellae in showers. Journal of
Hospital Infection, 16: 1-7.