LEGIONELLA - World Health Organization

5.5.2 Prepare management procedures
This step involves preparing management procedures, including corrective actions, for normal
and incident conditions. Corrective actions include repairing defects, and possibly re-treating
or discarding water that might be contaminated, to ensure that unsafe water is not supplied.
For most cooling tower systems, if HPC results exceed 5 × 10 5 CFU/ml or show a dramatically
increasing trend, an investigation should be carried out to determine the cause. The investigation
should include:
• a check of the chemical dosing — where manual slug dosing of antimicrobial is undertaken,
an examination of the relevant inspection reports concerning the amount and frequency
of antimicrobial addition; where an automatic dosing system is installed, the check
includes:
– a check of the level of biocide in the storage container
– an examination of the metering system for leaks, blockages and correct delivery of
antimicrobial into the cooling tower water
• internal and external examination of the cooling tower should be for cleanliness, deterioration
of construction materials and signs of tower pollution, including checking of the bleedoff
rate.
Based on the results of investigations, corrective action may include:
• a complete review of the water treatment programme, in cooperation with a water treatment
specialist
• remedial action, as required
• implementation of a routine cooling tower cleaning and disinfection procedure
• repeat water sampling for HPC after corrective procedures have been implemented
• performance of a new risk assessment after all corrective measures have been implemented.
5.5.3 Establish documentation and communication procedures
Table 5.2 gives an example of documentation for a routine monitoring and corrective action loop.
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS