Legionella Prevention

What is Legionella?

Legionella is a type of bacteria found naturally in water. It thrives in warm water (20 to 45 degrees C) and can multiply rapidly in cooling towers, hot water systems, spa pools, and other warm water systems. When inhaled as an aerosol, it causes Legionnaires' disease, a severe and sometimes fatal pneumonia.

Cooling towers are the most common source of Legionnaires' disease outbreaks because they generate aerosol drift that can spread over large distances, and the warm recirculating water is an ideal breeding ground.

Conditions That Promote Legionella Growth

• Water temperature 20 to 45 degrees C: The ideal growth range. Below 20 degrees C, Legionella is dormant. Above 60 degrees C, it is killed.
• Stagnant water: Low-flow areas in the tower basin, dead legs in piping, and unused parts of the system allow bacteria to multiply.
• Biofilm and sediment: Biofilm (slime) on tower surfaces protects bacteria from biocides. Sediment provides nutrients.
• Aerosol generation: The drift from cooling towers carries bacteria into the air, where it can be inhaled by people up to several kilometres away.
• Presence of amoebae: Legionella can live inside amoebae, which protect them from biocides and environmental stress.

Prevention Measures

1. Maintain a biocide program. Alternate between oxidising (chlorine, bromine) and non-oxidising biocides to prevent resistance. Dose continuously or at regular intervals.
2. Maintain drift eliminators in good condition. Replace damaged or degraded eliminators. They reduce drift by 99.5%+ when functioning correctly.
3. Clean the tower regularly. Remove sediment from the basin, descale the fill, and clean all surfaces. At least twice per year.
4. Eliminate dead legs and stagnant areas. All piping should have continuous flow. Remove or flush unused sections.
5. Monitor water quality. Test for Legionella bacteria and total bacteria count regularly (monthly minimum). Use dip slides or lab analysis.
6. Maintain correct pH. Biocides work best within specific pH ranges. Monitor and control pH.
7. Control corrosion and scale. Corrosion products and scale provide surfaces for biofilm and bacteria. Maintain the water treatment program.
8. Record all activities. Maintain a logbook of biocide dosing, cleaning, testing, and maintenance. This is a legal requirement in most jurisdictions.

Legal Obligations

• Registration: Cooling towers must be registered with the local health authority in most states.
• Maintenance program: A documented maintenance program must be in place, including cleaning, biocide dosing, and testing.
• Testing: Regular Legionella testing is required. Frequency varies by state but typically monthly to quarterly.
• Reporting: Positive Legionella results must be reported to health authorities. Immediate remediation is required.
• Records: All maintenance, testing, and corrective actions must be documented and retained for a minimum period (typically 5 years).