LEGIONELLA - World Health Organization
LEGIONELLA - World Health Organization
LEGIONELLA - World Health Organization
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Table . Water safety plan overv ew — cool ng towers and evaporat ve condensers<br />
Process step Water source Heat exchanger D str but on Cool ng tower<br />
Assess<br />
hazards and<br />
pr or t ze r sks<br />
(example)<br />
↓<br />
Ident fy control<br />
measures<br />
(example)<br />
↓<br />
Mon tor control<br />
measures<br />
(example)<br />
↓<br />
Prepare<br />
management<br />
procedures<br />
(example)<br />
Establ sh<br />
ver f cat on and<br />
surve llance<br />
(example)<br />
Develop<br />
support ng<br />
programmes<br />
(example)<br />
High nutrients<br />
and microbial<br />
load in source<br />
water<br />
Routine<br />
disinfection of<br />
water at 0.5 mg/l<br />
free residual<br />
chlorine<br />
Chlorine online<br />
(with chlorine/<br />
redox probe)<br />
Turbidity online<br />
Point-of-use filtration<br />
and disinfection<br />
programme;<br />
possible treatment<br />
for dissolved<br />
solids<br />
Elevated<br />
temperature and<br />
nutrients in<br />
biofilm, causing<br />
proliferation of<br />
legionellae<br />
Routine cleaning<br />
of the heat<br />
exchanger<br />
Operate condenser<br />
at minimum<br />
operating<br />
temperature<br />
Chlorine 0.5 mg/<br />
l free residual<br />
Chlorine and<br />
temperature<br />
online<br />
Shut down<br />
condenser; drain<br />
and implement<br />
physical cleaning<br />
and disinfection<br />
protocol<br />
Stagnant water<br />
in deadlegs<br />
(areas of little or<br />
no flow) in the<br />
pipework,<br />
resulting in<br />
proliferation of<br />
legionellae<br />
Treated water<br />
(chlorine 0.2–<br />
0.5 mg/l free<br />
chlorine residual<br />
and corrosion<br />
inhibitors)<br />
through the<br />
system<br />
Routine review<br />
of process diagram<br />
(desktop<br />
and onsite) to<br />
identify areas<br />
of concern or<br />
stagnation<br />
Remove<br />
deadlegs<br />
where possible<br />
Excessive drift<br />
loss from the<br />
tower exhaust,<br />
disseminating<br />
aerosols, and<br />
potentially<br />
legionellae, into<br />
the community<br />
Well-fitted and<br />
designed drift<br />
eliminatorsa Inspect drift<br />
eliminators<br />
monthly; look<br />
for drops and<br />
“splashouts”<br />
around the<br />
eliminators<br />
Regularly<br />
replace drift<br />
eliminators<br />
• Internal audit and external audit (by the health department) to confirm<br />
that operational monitoring and corrective actions are being undertaken<br />
as stated in the WSP<br />
• Monthly heterotrophic colony counts in the system and in the source<br />
water (to track trends and changes, rather than as an absolute<br />
indicator, and to be undertaken by an accredited laboratory)<br />
• Staff training and education; maintenance and calibration<br />
a Drift eliminators are inertial stripping devices that are used to remove water droplets.<br />
<strong>LEGIONELLA</strong> AND THE PREVENTION OF LEGIONELLOSIS
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