Legionnaires Disease

Background

Legionnaires’ disease is a potentially fatal form of pneumonia caused when very small droplets of water contaminated with legionella bacteria are inhaled.

It is estimated that there are 20 million evaporative cooling systems in the Western world [1]. There has never been a documented case of Legionnaires’ disease associated with a wetted media evaporative cooler [2].

Specific Legislation Relating to Legionnaires’ Disease

In addition to the Health and Safety at Work Act (HSWA), the Control of Substances Hazardous to Health Regulations (COSHH) and the Management of Health and Safety at Work Regulations (MHSWR) the Health and Safety Commission (HSC) produce an Approved Code of Practice (ACOP) Legionnaires’ Disease: The control of legionella bacteria in water systems L8.

It is the legal duty of employers and the responsibility of the managers of premises to comply with the above by completing a risk assessment on all water systems.

Why AFCOOLs are Safe

When a risk assessment is performed according to ACOP L8 there are 6 critical elements which must be addressed:

1. Avoidance of stagnant water: No dead legs exist in the system no stagnation occurs during normal operation of an EcoCooling cooler. When a unit is switched off the system
   automatically drains.
2. Low water operating temperature: The temperature of the water circulating in the evaporative cooler is approximately the “wet bulb temperature” of the air passing over the filters. In practice this means that, in a temperate climate, the water temperature rarely goes above 20C as shown even when the ambient air temperature exceeds 35C. It is generally accepted that Legionella is not a risk with water temperatures less than 20C
   
3. Avoidance of corrosion and scaling: To prevent corrosion all water contact surfaces are plastic. To control scale an AFCOOL measures the quantity of water supplied. When a concentration factor is reached the sump empties automatically and replenishes with fresh water. This has the effect of preventing scale and removing contaminants filtered from the air.
   
4. Use of Biocide (optional): Growth of organisms filtered from the air is suppressed by supplying the evaporative cooler with water with a low level of biocide from a brominator.
   
5. No production of aerosols: The design of EcoCooling coolers is such that only pure water evaporation without any production of droplets occurs as the air passes over the filters. This removes the mechanism for the transmission of
   infections such as Legionnaires’ disease.
   
6. Maintenance: By the implementation of a programmed maintenance system, the standards of hygiene are continued to provide a safe and secure system.

AFCOOL control systems have a comprehensive set of alarms to validate all of the key aspects of water process control an in particular remove any possibility of stagnation.

• Slow water fill
  
• Slow drain
  
• Slow evaporation
  
• Water probe logic failure

Generic Risk Assessment

When the above are subject to a risk assessment then it is normal for an AFCOOL to be classified as Low Risk. This is dependent upon installation, commissioning and routine
maintenance being performed according to EcoCooling procedures.

1. Evaporative Air-Conditioning: Applications for Environmentally Friendly Cooling by Ebel Dijkstra , Gert Jan Bom , Marja Tummers
   
2. ASHRE Guideline 12-2000 Minimising the Risk of Legionellosis Associated with Building Water Systems

Notification of Cooling Towers and Evaporative Condensers

A wetted media evaporative cooler does not have to be registered with regard to the Notification of Cooling Towers and Evaporative Condensers Regulations as a wetted media evaporative does not fit into the classification of a Cooling Tower or Evaporative condenser.