7
Anti-legionella recommendations (European standard CEN/TR 16355)
Information
Legionella is a small bacterium, of stick-like form, and is found naturally in fresh water.
Legionnaire's disease is a serious pulmonary infection caused by inhalation of the
Legionella pneumophilia
bacterium
and other species of
Legionella
. The bacterium is frequently to be found in the plumbing of houses, hotels and water
used in A/C and air cooling systems. The most effective measure against infection is to prevent the bacterium proliferating
in water circuits.
European standard CEN/TR 16355 provides guidelines for preventing the proliferation of Legionella in drinking water
systems, without substituting applicable local legislation.
General recommendations
“Conditions favourable to the proliferation of Legionella”. The following conditions are favourable to the proliferation
of Legionella:
•
Water temperature in the range 25 - 50
°
C. To reduce the proliferation of Legionella, the water temperature be
kept with these limits to prevent them growing or reduce their growth to a minimum. If this is not possible, the
drinking water system must be sanitised thermally;
•
Stagnant water. To prevent water stagnating for a long time, the drinking water system must be flushed or made
to run abundantly at least once a week;
•
Nutrients, biofilms and sediment in the circuit, including boilers, etc. Sediment may promote the proliferation of
Legionella and should be regularly eliminated from water storage devices, boilers and expansion/holding tanks
(for instance, once a year).
As regards storage heater like the present, if:
1)
the appliance is switched off for several months at a time or
2)
the water temperature is kept constant in the range 25 - 50
°
C,
the Legionella bacterium may grow inside the tank. If such circumstances, to reduce the proliferation of the bacterium,
one must run a thermal sanitisation cycle.
This cycle is suited to use in domestic hot water systems and complies with the guidelines for the prevention of
Legionella given in Table 2 of standard CEN/TR 16355 (see below).
Table 2 - Types of hot water system
Separate hot and cold water
Mixed hot and cold water
No
storage
Storage
No storage
upline of the
mixer valves
Storage upline
of the mixer
valves
No storage
upline of the
mixer valves
No
circulation
of hot water
Circulation
of hot water
No
circulation
of mixed
water
Circulation
of mixed
water
No
circulation
of mixed
water
Circulation
of mixed
water
No
circulation
of mixed
water
Circulation
of mixed
water
No
circulation
of mixed
water
Circulation
of mixed
water
Ref. in
Enclosure C
Temperature
Stagnation
Sediment
C.1
-
-
-
C.1
-
-
-
C.2
≥
50
°
C
e
≤
3 l
b
-
C.2
-
C.3
in
storage
heater
a
-
remove
c
C.2
C.4
≥
50
°
C
e
≤
3 l
b
remove
c
C.4
C.5
thermal
disinfection
d
-
-
-
C.5
-
-
C.6
thermal
disinfection
d
≤
3 l
b
-
C.6
-
C.7
in
storage
heater
a
-
remove
c
C.7
-
C.8
≥
50
°
C
e
thermal
disinfection
d
≤
3 l
b
remove
c
C.6
-
thermal
disinfection
d
C.9
-
-
C.9
-
-
thermal
disinfection
d
C.10
≤
3 l
b
-
a Temperature
≥
55
°
C all day or at least 1h a day
≥
60
°
C.
b Volume of water contained in the pipes between the circulation system and the most distant tap.
c Remove the sediment from the storage heater as required by local conditions, but no less frequently than once a year.
d Thermal disinfection for 20 minutes at 60
°
C, for 10 minutes at 65
°
C or 5 minutes at 70
°
C at all delivery points at least once
a week.
e The water temperature in the circulation circuit may not fall below 50
°
C.
-
Not required
This storage water heater is sold with a thermal disinfection cycle function not enabled for default; as a consequence,
if, for any reason, one of the above said “Conditions for Legionella growth” could occur; it’s hardly recommended to
enable such function rotating the knob up to maximum water temperature (>60
°
C).
However, the thermal disinfection cycle does not kill all Legionella bacteria in the storage tank. It follows that if the
water temperature setting is less than 55
°
C, the Legionella bacterium infection may reoccur.
Caution:
the water temperature in the tank can cause immediate serious burns. Children, disabled persons and
the aged are particularly at risk of burns. Check the water temperature before taking a bath or shower.
