Legionnaire’s disease also known as Legionellosis is an infectious disease caused by any type of Legionella bacteria but main contributor is Legionella pneumophila SG1. Typical symptoms can include shortness of breath, headaches and vomiting, similar to the symptoms of pneumonia.
Where is Legionella?
According to HSG 274, any water system that has the right environmental conditions could potentially be a source for legionella bacteria growth. There is a reasonably foreseeable legionella risk in your water system if:
water is stored or re-circulated as part of your system;
the water temperature in all or some part of the system may be between 20–45 °C;
there are deposits that can support bacterial growth, such as rust, sludge, scale and organic matter;
it is possible for water droplets to be produced and, if so, whether they can be dispersed;
How it spreads?
Legionellae is normally transmitted when a person breathes in very small water droplets, that have been populated by the Legionella bacteria. The droplets (aerosol) must be of a size that can pass into the lungs.
Managing the risk
The following precautions should be considered (HSG 274):
ensuring the release of water spray is properly controlled;
avoiding conditions that support growth of microorganisms, including legionella;
ensuring water cannot stagnate anywhere in the system by regular movement of water in all sections of the systems and by keeping pipe lengths as short as possible, and/or removing redundant pipework and deadlegs;
keeping the system and the water in it clean;
treating water to either control the growth of microorganisms, including legionella, or limit their ability to grow;
monitoring any control measures applied;
keeping records of these and other actions taken, such as maintenance and repair work.
In HSG 274 Chlorine Dioxide is mentioned as an effective disinfectant (when applied correctly) at controlling both legionella and biofilm growth in hot and cold-water systems.
Continuous dosing: 0.1-0.5 mg/L. Where the water is intended for human consumption the combined concentration of chlorine dioxide, chlorite and chlorate in the water entering supply do not exceed 0.5 mg/l as chlorine dioxide.
Shock dosing: 20-50mg/L. The system should be flushed through thoroughly after cleaning.