LEGIONELLA - World Health Organization

Table . Example documentat on for mon tor ng and correct ve act on
Process step Ind cator Mon tor ng
Chlorination Free
chlorine
ppm = parts per million
What Chlorine Not less than
0.5 ppm
How Diethyl-pphenylene
diamine
test kit
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS
Operat onal
l m t Correct ve act on
What Check pH of
water and the
chlorine dosing
pump
How pH probe and
observation of
the pump
When Weekly When Immediately
Where Tower
basin
Who Building engineer
If an outbreak of legionellosis occurs in the vicinity of a tower, that tower should be considered
as a potential source of infection; a precautionary decontamination is appropriate. Water samples
should be taken from the most contaminated point, and tests commenced immediately. The
standard from the International Organization for Standardization ISO 5667 (ISO, 2001)
can be used in developing sampling methods. Samples should be taken as near to the heat
source as possible. The suspected tower can then be immediately decontaminated, rather than
waiting for the results of the bacteriological tests, which may take 3–14 days.
In an outbreak, an emergency corrective action will be required, and procedures should already
be in place and staff trained in their implementation (e.g. see Box 5.3, above).
5.5.4 Verification
As part of a regular auditing programme, the operator or their water treatment company
should inspect cooling towers at least monthly (although shorter intervals may be determined
by the risk assessment for the system). Additional access hatches may need to be provided, to
facilitate inspection and cleaning of parts of the tower.
In a system in which risk assessment indicates cause for concern, verification of control of the
system may be established by the routine assessment of Legionella concentrations in the cooling
system. This verification should not precede or replace the routine monitoring of control
measures established for the system.