As the summer season approaches, those of you in the air-conditioning industry will be very busy, so I thought that I would do an article on “Legionnaires Disease”. It’s a very real hazard and potentially fatal if the proper precautions are not used. I know it’s not something that comes to mind as you go through your work day. But it’s something you really need to be aware of. Take a little time to read this article, and make sure you’re doing all you need to do, to be safe. I want to give you a little history on the disease and the things you can do to prevent it.

Legionnaires Disease is a common name for one of the several illnesses caused by Legionnaires’ disease bacteria. It is an infection of the lungs and is a form of pneumonia. The Centers of Disease Control and Prevention (CDC) first identified Legionnaires disease in 1977 as the cause of an outbreak of pneumonia that caused 34 deaths at a 1976 American Legion Convention in Philadelphia. Legionnaires Disease had undoubtedly caused previous pneumonia outbreaks, but the organism’s slow growth and special growth requirements prevented earlier discovery.

The likelihood of contracting Legionnaires’ disease depends on the level of contamination in the water source, the susceptibility of the person exposed, and the intensity of exposure. In the United States, Legionnaires’ disease is fairly common and serious. It is one of the top three causes of non-epidemic, community-acquired pneumonia.

Typically, but not uniformly, the first symptoms are general malaise and headache, followed by high fever, often accompanied by chills. Coughing (often without sputum production), shortness of breath, pleurisy-like pain and abdominal distress are common, and occasionally some mental confusion is present. Although healthy individuals can contract Legionnaires’ disease, the most common patients are elderly or debilitated individuals or persons whose immunity is suppressed by drugs or disease.

Legionnaires’ disease treatment requires the use of antibiotics. Early treatment reduces the severity of symptoms and improves chances of recovery. The drugs of choice belong to a class of antibiotics called macrolides. They include azithromycin, erythromycin, and clarithromycin.

Potential sources of Legionnaires Disease :

Water systems in workplaces are potential sources of Legionnaires’ disease bacteria.

The primary sources of exposure to contaminated water in commercial and industrial facilities are water-cooled, heat transfer systems such as cooling towers or fluid coolers, and warm water sources such as domestic hot-water systems.

Cooling Towers, Evaporative Condensers, and Fluid Coolers

Cooling towers, evaporative condensers, and fluid coolers use a fan to move air through a recirculated water system. This allows a considerable amount of water vapor and sometimes droplets to be introduced into the surroundings, despite the presence of drift eliminators designed to limit droplet release. This water may be in the ideal temperature range for Legionnaires’ disease bacteria growth, 20°-50°C (68°-122°F). Good maintenance is necessary, both to control the growth and for effective operation.

What to consider in the system design :

Important design features include easy access or easily disassembled components to allow cleaning of internal parts including the packing (fill). The following features should be considered in the system design:

1. Enclosure of the system will prevent drift of water vapor.
2. Design features that minimize the spray generated by these systems are desirable.
3. System design should recognize the value of operating with low sump-water temperatures.
4. Each sump should be equipped with a “bleed,” and make-up water should be supplied to reduce the concentration of dissolved solids.
5. High-efficiency drift eliminators are essential for all cooling towers
6. Older systems can usually be retrofitted with high-efficiency models.
7. A well-designed and well-fitted drift eliminator can greatly reduce water loss and potential for exposure.
8. The system should be properly monitored and maintained according to manufacturers’ recommendations to prevent buildup of scale, sediment, and bio-fouling. Visual inspection and periodic maintenance of the system are the best ways to control growth of LDB and related organisms.

Biocides:

• Add chemical bio-cides to control LDB growth. Obtain information on appropriate biocide selection and use from equipment manufacturers or from companies experienced with the particular system used.
• High concentrations of organic matter and dissolved solids in the water will reduce the effectiveness of any biocidal agent.

Temperature:

• Maintain sump water at a low temperature (20°C, 68°F) to control LDB growth.
• Sump-water temperatures depend on tower design, heat load, flow rate, and ambient dry-bulb and wet-bulb temperatures.
• Under ideal conditions, sump-water temperatures in evaporative devices approach the ambient wet-bulb temperature, and may be low enough to limit LDB amplification.

Cleaning Schedule:

After a contaminated system has been treated, sampling can be used to verify the effectiveness of the treatment. Subsequent testing of cooling-system water at the following intervals can verify that there is no significant re-growth of LDB:

• Test weekly for the first month after return to operation.
• Test every two weeks for the next two months.
• Test monthly for the next three months.
• Clean and disinfect cooling towers quarterly or at least twice a year if the unit is not used year round. Do these before initial start-up at the beginning of the cooling season and after shut-down in the fall.
• Any system that has been out of service for an extended period should be cleaned and disinfected.
• New systems require cleaning and disinfecting because construction material residue can contribute to LDB growth.

Acceptable cleaning procedures are outlined as follows:

1. Inspect equipment monthly.
2. Drain and clean quarterly or at least twice a year if the unit is not used year round.
3. Treat circulating water for control of microorganisms, scale, and corrosion.
4. This should include the use of bio-cides, and rust inhibitors, supplied by continuous feed.
5. Monthly micro-biologic analysis is needed to ensure control of biological contamination.
6. Maintain an up-to-date description of the operating system (which includes all components cooled by the system) and details of the make-up water to the system.
7. Written procedures for proper operation and maintenance of the system should indicate the use of scale and corrosion inhibitors and anti-foaming agents. Written records of biocide or chlorine use should be readily available.

Chemical additives:

Traditional oxidizing agents such as chlorine and bromine have been proven effective in controlling Legionnaires’ disease bacteria (LDB) in cooling towers. Continuous chlorination at low free residual levels can be effective in controlling LDB growth.

It is important that the proper oxidant level be established and maintained because free residual chlorine above 1 mg/L may be corrosive to metals in the system and may damage wood used in cooling towers. However, free residual levels below 1 mg/L may not adequately control LDB growth.

Chlorine also combines with organic substances in water to form toxic by-products that are of environmental concern. Frequent monitoring and control of pH is essential for maintaining adequate levels of free residual chlorine. Above a pH of 8.0, chlorine effectiveness is greatly reduced. Proper control of pH will maintain the effectiveness of chlorination and minimize corrosion.

Bromine is an effective oxidizing biocide. Bromine is frequently added as a bromide salt and generated by reaction with chlorine. Its effectiveness is less dependent on the pH of the water than chlorine. Therefore is less corrosive and produces less toxic environmental by-products.

Possible contamination sites:

• Ice machines: In hospitals supplied by cold-water lines near heat sources that promote LDB growth.
• Water tanks: That allows water to remain un-circulated for long periods also can promote bacterial growth. Cross-contamination of a domestic cold-water system with another system should always be suspected of promoting bacterial growth.
• Emergency water systems: such as fire sprinkling systems, safety showers, and eye wash stations are other domestic cold-water sources from which LDB have been cultured. These systems experience little water flow and can be subject to periods of elevated temperatures. In addition, operation of these devices will aerosolize water. For these reasons, emergency water systems should be considered potential sources of LDB, although no documented cases of legionellosis have been associated with these sources.

I’ve tried to give you a variety of information, the history of the disease, how you can contract it, and the safety precautions. I have a great deal more information, if you would like to discuss this subject further. The main thing is to be careful, wear a face-mask or a respirator, wear gloves and safety goggles. Test the system you working on; make there is no harmful bacteria.