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Dave Yates (PAH)
Member Posts: 2,162
OSHA-CDC (Legionnaires' Disease) - Maintenance Docs
OSHA Technical Manual Sec. II Chap. 7, LEGIONNAIRES' DISEASE
BIOCIDE
Unfortunately, measurements of water quality such as total bacterial counts, total dissolved solids, and pH have not proven to be good indicators of Legionella levels in cooling towers. Periodic use of biocides is needed to ensure control of Legionella growth.
Little information exists on the demonstrated effectiveness of many commercial biocides for preventing Legionella growth in actual operations. Recent Australian studies indicate that Fentichlor [2,2'-thiobis (4-chlorophenol) used weekly for 4 hours at 200 ppm, or bromo-chloro-dimethyl-hydantoin (BCD) in a slow-release cartridge at an initial concentration of 300 ppm are effective in controlling the growth of Legionella. There are no U.S. suppliers of Fentichlor, although the chemical is licensed by the EPA for water treatment in cooling towers. Towerbrom 60M(TM), a chlorotriazine and sodium bromide salt mixture, has been reported to be effective when alternated with BCD for control of Legionella in U.S. studies of Legionella contamination of cooling towers. The Australian study also indicates that quaternary ammonium compounds, widely used for control of bio-fouling in cooling towers, are not effective in controlling Legionella.
Traditional oxidizing agents such as chlorine and bromine have been proven effective in controlling Legionella in cooling towers. Continuous chlorination at low free residual levels can be effective in controlling Legionella growth. It is important, however, that the proper oxidant level be established and maintained because free residual chlorine above 1 ppm may be corrosive to metals in the system and may damage wood used in cooling towers; free residual levels below 1 ppm may not adequately control Legionella 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. It is frequently added as a bromide salt and generated by reaction with chlorine. Bromine's effectiveness is less dependent than chlorine on the pH of the water; it is less corrosive; and it also produces less toxic environmental by-products.
The effectiveness of any water-treatment regimen depends on the use of clean water. High concentrations of organic matter and dissolved solids in the water will reduce the effectiveness of any biocidal agent. Each sump should be equipped with a "bleed," and make-up water should be supplied to reduce the concentration of dissolved solids.
DESIGN
One of the most effective means of controlling the growth of Legionella is to maintain sump water at a low temperature. 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 that may be low enough to limit Legionella amplification. System design should recognize the value of operating with low sump-water temperatures.
High-efficiency drift eliminators are essential for all cooling towers. Older systems can usually be retrofitted with high-efficiency models. A well-designed and well-fitted drift eliminator can greatly reduce water loss and potential for exposure.
Other important design features include easy access or easily disassembled components to allow cleaning of internal components including the packing (fill). Enclosure of the system will prevent unnecessary drift of water vapor, and other design features to minimize the spray generated by these systems are also desirable.
FREQUENCY OF CLEANING
Cooling towers should be cleaned and disinfected at least twice a year. Normally this maintenance will be performed before initial start-up at the beginning of the cooling season and after shut-down in the fall. Systems with heavy bio-fouling or high levels of Legionella may require additional cleaning. 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 Legionella growth.
WISCONSIN PROTOCOL
Acceptable cleaning procedures include those described in the Wisconsin Protocol. This procedure calls for an initial shock treatment with 50 ppm free residual (total) chlorine, addition of detergent to disperse bio-fouling, maintenance of 10 ppm chlorine for 24 hours, and a repeat of the cycle until there is no visual evidence of biofilms. To prevent exposure during cleaning and maintenance, wear proper personal protective equipment: a Tyvek-type suit with a hood, protective gloves, and a properly fitted respirator with a high-efficiency particulate (HEPA) filter or a filter effective at removing one-micron particles.
DOMESTIC HOT-WATER SYSTEMS
BACKGROUND
Domestic hot-water systems are frequently linked to Legionnaires' outbreaks. The term "domestic" applies to all nonprocess water used for lavatories, showers, drinking fountains, etc., in commercial, residential, and industrial settings. Disease transmission from domestic hot water may be by inhalation or aspiration of Legionella-contaminated aerosolized water. Water heaters that are maintained below 60 degrees C (140 degrees F) and contain scale and sediment tend to harbor the bacteria and provide essential nutrients for commensal micro-organisms that foster growth of L. pneumophila. Large water heaters like those used in hospitals or industrial settings frequently contain cool zones near the base where cold water enters and scale and sediment accumulate. The temperature and sediment in these zones can provide ideal conditions for amplification of the organism. Dead legs and nonrecirulated plumbing lines that allow hot water to stagnate also provide areas for growth of the organism.
DESIGN
Water systems designed to recirculate water and minimize dead legs will reduce stagnation. If potential for scalding exists, appropriate, fail-safe scald-protection equipment should be employed. For example, pressure-independent, thermostatic mixing valves at delivery points can reduce delivery temperatures. Point-of-use water heaters can eliminate stagnation of hot water in infrequently used lines. Proper insulation of hot-water lines and heat tracing of specific lines can help maintain distribution and delivery temperatures.
MAINTENANCE
To minimize the growth of Legionella in the system, domestic hot water should be stored at a minimum of 60 degrees C (140 degrees F) and delivered at a minimum of 50 degrees C (122 degrees F) to all outlets. The hot-water tank should be drained periodically to remove scale and sediment and cleaned with chlorine solution if possible. The tank should be thoroughly rinsed to remove excess chlorine before reuse.
Eliminate dead legs when possible, or install heat tracing to maintain 50 degrees C (122 degrees F) in the lines. Rubber or silicone gaskets provide nutrients for the bacteria, and removing them will help control growth of the organism. Frequent flushing of these lines should also reduce growth.
Domestic hot-water recirculation pumps should run continuously. They should be excluded from energy conservation measures.
CONTROL
Raising the water-heater temperature can control or eliminate Legionella growth. Pasteurize the hot water system by raising the water-heater temperature to a minimum of 70 degrees C (158 degrees F) for 24 hours and then flushing each outlet for 20 minutes. It is important to flush all taps with the hot water because stagnant areas can "re-seed" the system. Exercise caution to avoid serious burns from the high water temperatures used in Pasteurization.
Periodic chlorination of the system at the tank to produce 10 ppm free residual chlorine and flushing of all taps until a distinct odor of chlorine is evident is another means of control. In-line chlorinators can be installed in the hot water line; however, chlorine is quite corrosive and will shorten the service life of metal plumbing. Control of the pH is extremely important to ensure that there is adequate residual chlorine in the system
Alternative means to control Legionella growth include the use of metal ions such as copper or silver (which have a biocidal effect) in solution. Ozonization injects ozone into the water. Ultraviolet (UV) radiation also kills microorganisms. Commercial, in-line UV systems are effective and can be installed on incoming water lines or on recirculating systems, but stagnant zones may diminish the effectiveness of this treatment. Scale buildup on the UV lamp surface can rapidly reduce light intensity and requires frequent maintenance to ensure effective operation.
DOMESTIC COLD-WATER SYSTEMS
Domestic cold water systems are not a major problem for Legionella growth. Maintaining cold-water lines below 20 degrees C will limit the potential for amplification of the bacteria. It is surprising, however, that elevated levels of Legionella have been measured in ice machines in hospitals. Cold-water lines near heat sources in the units are believed to have caused the amplification.
Dental water lines have recently been recognized as common sources of water contaminated with high concentrations of microorganisms including Legionella. However, to date an increased risk of disease among dental staff or patients has not been demonstrated. Dental water line operating conditions are especially appropriate for Legionella proliferation because the water is stagnant a majority of the time, the narrow plastic tubing encourages biofilm formation, and the water temperature is usually 20 degrees C (68 degrees F) or higher-some systems maintain water at 37 degrees C (98.6 degrees F). Filtration of water at the point of use with replaceable, in-line, 1-micron filters is a FDA approved method of minimizing risk to patients and staff in a dental facility.
Water tanks that allow water to remain uncirculated for long periods can also promote growth of bacteria. Such tanks should be eliminated or designed to reduce storage time to a day or less. They should also be covered to prevent contamination and protected from temperature extremes.
Cross-contaminations of the domestic cold-water system with other systems should always be suspected. All connections to process water should be protected by a plumbing code-approved device (e.g., back-flow preventer, air gap, etc.).
If significant contamination of the domestic cold water system occurs, the source of contamination should be determined. Inspect the system for "dead legs" and areas where water may stagnate. Elimination of these sections or frequent flushing of taps to drain the stagnant areas may be necessary to limit growth of the organism. Insulate cold-water lines that are close to hot-water lines to reduce the temperature in the line.
If the cold-water lines have significant contamination, hyperchlorination can eradicate Legionella. Free chlorine levels of 20 to 50 ppm are allowed to remain for one hour at 50 ppm, or two hours at 20 ppm. Faucets are then allowed to run until the odor of chlorine is present, and the water is allowed to remain for approximately two hours.
CDC - APPENDIX B Maintenance
MAINTENANCE PROCEDURES TO DECREASE SURVIVAL AND MULTIPLICATION OF LEGIONELLA SPP. IN POTABLE-WATER DISTRIBUTION SYSTEMS
I. Providing Water at > or = 50ºC at All Points in the Heated Water System, Including the Taps
This requires that water in calorifiers (water heaters) be maintained at > or = 60ºC. In the United Kingdom, where maintenance of water temperatures at > or = 50ºC in hospitals has been mandated, installation of blending or mixing valves at or near taps to reduce the water temperature to Legionella spp. can multiply even in short segments of pipe containing water at this temperature. Increasing the flow rate from the hot-water-circulation system may help lessen the likelihood of water stagnation and cooling. Insulation of plumbing to ensure delivery of cold (<20ºc) water to water heaters (and to cold-water outlets) may diminish the opportunity for bacterial multiplication. "Dead legs" or capped spurs within the plumbing system provide areas of stagnation and cooling to <50ºC regardless of the circulating-water temperature; these segments may need to be removed to prevent colonization.](728) Rubber fittings within plumbing systems have been associated with persistent colonization, and replacement of these fittings may be required for Legionella spp. eradication.(729)
II. Continuous Chlorination to Maintain Concentrations of Free Residual Chlorine at 1-2 mg/L at the Tap
This requires the placement of flow-adjusted, continuous injectors of chlorine throughout the water distribution system. Adverse effects of continuous chlorination include accelerated corrosion of plumbing resulting in system leaks and production of potentially carcinogenic trihalomethanes. However, when levels of free residual chlorine are below 3 mg/L, trihalomethane levels are kept below the maximum "safety level" recommended by the Environmental Protection Agency.
CDC - APPENDIX D CLEANING TOWERS
PROCEDURE FOR CLEANING COOLING TOWERS AND RELATED EQUIPMENT (Adapted from the Emergency Protocol in Control of Legionella spp. in Cooling Towers: Summary Guidelines.[464])
I. Preparatory to Chemical Disinfection and Mechanical Cleaning
A. Provide protective equipment to workers who would perform the disinfection, to prevent their exposure to (a) chemicals used for disinfection and (b) aerosolized water containing Legionella spp. Protective equipment may include full-length protective clothing, boots, gloves, goggles, and a full- or half-face mask that combines high efficiency particulate air filter and chemical cartridges to protect against airborne chlorine levels of up to 10 mg/L.
B. Shut off cooling-tower.
1. If possible, shut off heat source.
2. Shut off fans, if present, on the cooling tower/evaporative condenser (CT/EC).
3. Shut off the system blowdown (purge) valve. Shut off automated blowdown controller, if present, and set system controller to manual.
4. Keep make-up water valves open.
5. Close building air-intake vents within at least 30 meters of the CT/EC until after the cleaning procedure is complete.
6. Continue operating pumps for water circulation through the CT/EC.
II. Chemical Disinfection
A. Add fast-release, chlorine-containing disinfectant in pellet, granular, or liquid form, and follow safety instructions on the product label. Examples of disinfectants include sodium hypochlorite (NaOCl) or calcium hypochlorite (Ca[OCl]2), calculated to achieve initial free residual chlorine (FRC) of 50 mg/L, i.e., 3.0 lbs (1.4 kg) industrial grade NaOCl (12-15% available Cl) per 1,000 gallons of CT/EC water; 10.5 lbs (4.8 kg) domestic grade NaOCl (3-5% available Cl) per 1,000 gallons of CT/EC water; or 0.6 lb (0.3 kg) Ca(OCl)2 per 1,000 gallons of CT/EC water. If significant biodeposits are present, additional chlorine may be required. If the volume of water in CT/EC is not known, it can be estimated (in gallons) by multiplying the recirculation rate in gallons/minute by 10, or the refrigeration capacity in tons by 30. Other appropriate compounds may be suggested by a water-treatment specialist.
B. Record the type and quality of all chemicals used for disinfection, exact time the chemicals are added to the system, and time and results of measurements of (FRC) and pH.
C. Add dispersant simultaneously with or within 15 minutes of adding disinfectant. The dispersant is best added by first dissolving it in water and adding the solution to a turbulent zone in the water system. Examples of low or non-foaming, silicate-based dispersants are: automatic-dishwasher compounds, such as Cascade* or Calgonite* or an equivalent product. Dispersants are added at 10-25 lbs. (4.5-11.25 kg) per 1,000 gallons of CT/EC water.
D. After adding disinfectant and dispersant, continue circulating the water through the system. Monitor FRC by using an FRC-measuring device, such as a swimming pool test kit, and measure the pH with a pH meter every 15 minutes for 2 hours. Add chlorine as needed to maintain FRC at > or = 10 mg/L. Since the biocidal effect of chlorine is reduced at higher pH, adjust pH to 7.5-8.0. The pH may be lowered by using any acid (eg, muriatic acid or sulfuric acid used for maintenance of swimming pools) that is compatible with the treatment chemicals.
E. Two hours after adding disinfectant and dispersant or after FRC level is stable at 10 mg/L, monitor at 2-hour intervals and maintain FRC at 10 mg/L for 24 hours.
F. After FRC level has been maintained at 10 mg/L for 24 hours, drain the system. CT/EC water may be safely drained to the sanitary sewer. Municipal water and sewerage authorities should be contacted regarding local regulations. If a sanitary sewer is not available, consult local or state authorities (eg, Department of Natural Resources) regarding disposal of water. If necessary, the drain-off may be dechlorinated by dissipation or chemical neutralization with sodium bisulfite.
G. Refill system with water and repeat procedure outlined in steps 2-6 in I-B above.
III. Mechanical Cleaning
A. After water from the second chemical disinfection has been drained, shut down the CT/EC.
B. Inspect all water contact areas for sediment, sludge, and scale. Using brushes and/or a low-pressure water hose, thoroughly clean all CT/EC water contact areas including basin, sump, fill, spray nozzles, and fittings. Replace components as needed.
C. If possible, clean CT/EC water contact areas within the chillers.
IV. After Mechanical Cleaning
A. Fill the system with water, and add chlorine to achieve FRC level of 10 mg/L.
B. Circulate water for one hour, then open blowdown valve and flush the entire system until the water is free of turbidity.
C. Drain the system.
D. Open any air intake vents that were closed prior to cleaning.
E. Fill the system with water. CT/EC may be put back into service using an effective water-treatment program.
* Use of product names is for identification only and does not imply endorsement by the Public Health Service or the U.S. Department of Health and Human Services.
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OSHA Technical Manual Sec. II Chap. 7, LEGIONNAIRES' DISEASE
BIOCIDE
Unfortunately, measurements of water quality such as total bacterial counts, total dissolved solids, and pH have not proven to be good indicators of Legionella levels in cooling towers. Periodic use of biocides is needed to ensure control of Legionella growth.
Little information exists on the demonstrated effectiveness of many commercial biocides for preventing Legionella growth in actual operations. Recent Australian studies indicate that Fentichlor [2,2'-thiobis (4-chlorophenol) used weekly for 4 hours at 200 ppm, or bromo-chloro-dimethyl-hydantoin (BCD) in a slow-release cartridge at an initial concentration of 300 ppm are effective in controlling the growth of Legionella. There are no U.S. suppliers of Fentichlor, although the chemical is licensed by the EPA for water treatment in cooling towers. Towerbrom 60M(TM), a chlorotriazine and sodium bromide salt mixture, has been reported to be effective when alternated with BCD for control of Legionella in U.S. studies of Legionella contamination of cooling towers. The Australian study also indicates that quaternary ammonium compounds, widely used for control of bio-fouling in cooling towers, are not effective in controlling Legionella.
Traditional oxidizing agents such as chlorine and bromine have been proven effective in controlling Legionella in cooling towers. Continuous chlorination at low free residual levels can be effective in controlling Legionella growth. It is important, however, that the proper oxidant level be established and maintained because free residual chlorine above 1 ppm may be corrosive to metals in the system and may damage wood used in cooling towers; free residual levels below 1 ppm may not adequately control Legionella 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. It is frequently added as a bromide salt and generated by reaction with chlorine. Bromine's effectiveness is less dependent than chlorine on the pH of the water; it is less corrosive; and it also produces less toxic environmental by-products.
The effectiveness of any water-treatment regimen depends on the use of clean water. High concentrations of organic matter and dissolved solids in the water will reduce the effectiveness of any biocidal agent. Each sump should be equipped with a "bleed," and make-up water should be supplied to reduce the concentration of dissolved solids.
DESIGN
One of the most effective means of controlling the growth of Legionella is to maintain sump water at a low temperature. 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 that may be low enough to limit Legionella amplification. System design should recognize the value of operating with low sump-water temperatures.
High-efficiency drift eliminators are essential for all cooling towers. Older systems can usually be retrofitted with high-efficiency models. A well-designed and well-fitted drift eliminator can greatly reduce water loss and potential for exposure.
Other important design features include easy access or easily disassembled components to allow cleaning of internal components including the packing (fill). Enclosure of the system will prevent unnecessary drift of water vapor, and other design features to minimize the spray generated by these systems are also desirable.
FREQUENCY OF CLEANING
Cooling towers should be cleaned and disinfected at least twice a year. Normally this maintenance will be performed before initial start-up at the beginning of the cooling season and after shut-down in the fall. Systems with heavy bio-fouling or high levels of Legionella may require additional cleaning. 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 Legionella growth.
WISCONSIN PROTOCOL
Acceptable cleaning procedures include those described in the Wisconsin Protocol. This procedure calls for an initial shock treatment with 50 ppm free residual (total) chlorine, addition of detergent to disperse bio-fouling, maintenance of 10 ppm chlorine for 24 hours, and a repeat of the cycle until there is no visual evidence of biofilms. To prevent exposure during cleaning and maintenance, wear proper personal protective equipment: a Tyvek-type suit with a hood, protective gloves, and a properly fitted respirator with a high-efficiency particulate (HEPA) filter or a filter effective at removing one-micron particles.
DOMESTIC HOT-WATER SYSTEMS
BACKGROUND
Domestic hot-water systems are frequently linked to Legionnaires' outbreaks. The term "domestic" applies to all nonprocess water used for lavatories, showers, drinking fountains, etc., in commercial, residential, and industrial settings. Disease transmission from domestic hot water may be by inhalation or aspiration of Legionella-contaminated aerosolized water. Water heaters that are maintained below 60 degrees C (140 degrees F) and contain scale and sediment tend to harbor the bacteria and provide essential nutrients for commensal micro-organisms that foster growth of L. pneumophila. Large water heaters like those used in hospitals or industrial settings frequently contain cool zones near the base where cold water enters and scale and sediment accumulate. The temperature and sediment in these zones can provide ideal conditions for amplification of the organism. Dead legs and nonrecirulated plumbing lines that allow hot water to stagnate also provide areas for growth of the organism.
DESIGN
Water systems designed to recirculate water and minimize dead legs will reduce stagnation. If potential for scalding exists, appropriate, fail-safe scald-protection equipment should be employed. For example, pressure-independent, thermostatic mixing valves at delivery points can reduce delivery temperatures. Point-of-use water heaters can eliminate stagnation of hot water in infrequently used lines. Proper insulation of hot-water lines and heat tracing of specific lines can help maintain distribution and delivery temperatures.
MAINTENANCE
To minimize the growth of Legionella in the system, domestic hot water should be stored at a minimum of 60 degrees C (140 degrees F) and delivered at a minimum of 50 degrees C (122 degrees F) to all outlets. The hot-water tank should be drained periodically to remove scale and sediment and cleaned with chlorine solution if possible. The tank should be thoroughly rinsed to remove excess chlorine before reuse.
Eliminate dead legs when possible, or install heat tracing to maintain 50 degrees C (122 degrees F) in the lines. Rubber or silicone gaskets provide nutrients for the bacteria, and removing them will help control growth of the organism. Frequent flushing of these lines should also reduce growth.
Domestic hot-water recirculation pumps should run continuously. They should be excluded from energy conservation measures.
CONTROL
Raising the water-heater temperature can control or eliminate Legionella growth. Pasteurize the hot water system by raising the water-heater temperature to a minimum of 70 degrees C (158 degrees F) for 24 hours and then flushing each outlet for 20 minutes. It is important to flush all taps with the hot water because stagnant areas can "re-seed" the system. Exercise caution to avoid serious burns from the high water temperatures used in Pasteurization.
Periodic chlorination of the system at the tank to produce 10 ppm free residual chlorine and flushing of all taps until a distinct odor of chlorine is evident is another means of control. In-line chlorinators can be installed in the hot water line; however, chlorine is quite corrosive and will shorten the service life of metal plumbing. Control of the pH is extremely important to ensure that there is adequate residual chlorine in the system
Alternative means to control Legionella growth include the use of metal ions such as copper or silver (which have a biocidal effect) in solution. Ozonization injects ozone into the water. Ultraviolet (UV) radiation also kills microorganisms. Commercial, in-line UV systems are effective and can be installed on incoming water lines or on recirculating systems, but stagnant zones may diminish the effectiveness of this treatment. Scale buildup on the UV lamp surface can rapidly reduce light intensity and requires frequent maintenance to ensure effective operation.
DOMESTIC COLD-WATER SYSTEMS
Domestic cold water systems are not a major problem for Legionella growth. Maintaining cold-water lines below 20 degrees C will limit the potential for amplification of the bacteria. It is surprising, however, that elevated levels of Legionella have been measured in ice machines in hospitals. Cold-water lines near heat sources in the units are believed to have caused the amplification.
Dental water lines have recently been recognized as common sources of water contaminated with high concentrations of microorganisms including Legionella. However, to date an increased risk of disease among dental staff or patients has not been demonstrated. Dental water line operating conditions are especially appropriate for Legionella proliferation because the water is stagnant a majority of the time, the narrow plastic tubing encourages biofilm formation, and the water temperature is usually 20 degrees C (68 degrees F) or higher-some systems maintain water at 37 degrees C (98.6 degrees F). Filtration of water at the point of use with replaceable, in-line, 1-micron filters is a FDA approved method of minimizing risk to patients and staff in a dental facility.
Water tanks that allow water to remain uncirculated for long periods can also promote growth of bacteria. Such tanks should be eliminated or designed to reduce storage time to a day or less. They should also be covered to prevent contamination and protected from temperature extremes.
Cross-contaminations of the domestic cold-water system with other systems should always be suspected. All connections to process water should be protected by a plumbing code-approved device (e.g., back-flow preventer, air gap, etc.).
If significant contamination of the domestic cold water system occurs, the source of contamination should be determined. Inspect the system for "dead legs" and areas where water may stagnate. Elimination of these sections or frequent flushing of taps to drain the stagnant areas may be necessary to limit growth of the organism. Insulate cold-water lines that are close to hot-water lines to reduce the temperature in the line.
If the cold-water lines have significant contamination, hyperchlorination can eradicate Legionella. Free chlorine levels of 20 to 50 ppm are allowed to remain for one hour at 50 ppm, or two hours at 20 ppm. Faucets are then allowed to run until the odor of chlorine is present, and the water is allowed to remain for approximately two hours.
CDC - APPENDIX B Maintenance
MAINTENANCE PROCEDURES TO DECREASE SURVIVAL AND MULTIPLICATION OF LEGIONELLA SPP. IN POTABLE-WATER DISTRIBUTION SYSTEMS
I. Providing Water at > or = 50ºC at All Points in the Heated Water System, Including the Taps
This requires that water in calorifiers (water heaters) be maintained at > or = 60ºC. In the United Kingdom, where maintenance of water temperatures at > or = 50ºC in hospitals has been mandated, installation of blending or mixing valves at or near taps to reduce the water temperature to Legionella spp. can multiply even in short segments of pipe containing water at this temperature. Increasing the flow rate from the hot-water-circulation system may help lessen the likelihood of water stagnation and cooling. Insulation of plumbing to ensure delivery of cold (<20ºc) water to water heaters (and to cold-water outlets) may diminish the opportunity for bacterial multiplication. "Dead legs" or capped spurs within the plumbing system provide areas of stagnation and cooling to <50ºC regardless of the circulating-water temperature; these segments may need to be removed to prevent colonization.](728) Rubber fittings within plumbing systems have been associated with persistent colonization, and replacement of these fittings may be required for Legionella spp. eradication.(729)
II. Continuous Chlorination to Maintain Concentrations of Free Residual Chlorine at 1-2 mg/L at the Tap
This requires the placement of flow-adjusted, continuous injectors of chlorine throughout the water distribution system. Adverse effects of continuous chlorination include accelerated corrosion of plumbing resulting in system leaks and production of potentially carcinogenic trihalomethanes. However, when levels of free residual chlorine are below 3 mg/L, trihalomethane levels are kept below the maximum "safety level" recommended by the Environmental Protection Agency.
CDC - APPENDIX D CLEANING TOWERS
PROCEDURE FOR CLEANING COOLING TOWERS AND RELATED EQUIPMENT (Adapted from the Emergency Protocol in Control of Legionella spp. in Cooling Towers: Summary Guidelines.[464])
I. Preparatory to Chemical Disinfection and Mechanical Cleaning
A. Provide protective equipment to workers who would perform the disinfection, to prevent their exposure to (a) chemicals used for disinfection and (b) aerosolized water containing Legionella spp. Protective equipment may include full-length protective clothing, boots, gloves, goggles, and a full- or half-face mask that combines high efficiency particulate air filter and chemical cartridges to protect against airborne chlorine levels of up to 10 mg/L.
B. Shut off cooling-tower.
1. If possible, shut off heat source.
2. Shut off fans, if present, on the cooling tower/evaporative condenser (CT/EC).
3. Shut off the system blowdown (purge) valve. Shut off automated blowdown controller, if present, and set system controller to manual.
4. Keep make-up water valves open.
5. Close building air-intake vents within at least 30 meters of the CT/EC until after the cleaning procedure is complete.
6. Continue operating pumps for water circulation through the CT/EC.
II. Chemical Disinfection
A. Add fast-release, chlorine-containing disinfectant in pellet, granular, or liquid form, and follow safety instructions on the product label. Examples of disinfectants include sodium hypochlorite (NaOCl) or calcium hypochlorite (Ca[OCl]2), calculated to achieve initial free residual chlorine (FRC) of 50 mg/L, i.e., 3.0 lbs (1.4 kg) industrial grade NaOCl (12-15% available Cl) per 1,000 gallons of CT/EC water; 10.5 lbs (4.8 kg) domestic grade NaOCl (3-5% available Cl) per 1,000 gallons of CT/EC water; or 0.6 lb (0.3 kg) Ca(OCl)2 per 1,000 gallons of CT/EC water. If significant biodeposits are present, additional chlorine may be required. If the volume of water in CT/EC is not known, it can be estimated (in gallons) by multiplying the recirculation rate in gallons/minute by 10, or the refrigeration capacity in tons by 30. Other appropriate compounds may be suggested by a water-treatment specialist.
B. Record the type and quality of all chemicals used for disinfection, exact time the chemicals are added to the system, and time and results of measurements of (FRC) and pH.
C. Add dispersant simultaneously with or within 15 minutes of adding disinfectant. The dispersant is best added by first dissolving it in water and adding the solution to a turbulent zone in the water system. Examples of low or non-foaming, silicate-based dispersants are: automatic-dishwasher compounds, such as Cascade* or Calgonite* or an equivalent product. Dispersants are added at 10-25 lbs. (4.5-11.25 kg) per 1,000 gallons of CT/EC water.
D. After adding disinfectant and dispersant, continue circulating the water through the system. Monitor FRC by using an FRC-measuring device, such as a swimming pool test kit, and measure the pH with a pH meter every 15 minutes for 2 hours. Add chlorine as needed to maintain FRC at > or = 10 mg/L. Since the biocidal effect of chlorine is reduced at higher pH, adjust pH to 7.5-8.0. The pH may be lowered by using any acid (eg, muriatic acid or sulfuric acid used for maintenance of swimming pools) that is compatible with the treatment chemicals.
E. Two hours after adding disinfectant and dispersant or after FRC level is stable at 10 mg/L, monitor at 2-hour intervals and maintain FRC at 10 mg/L for 24 hours.
F. After FRC level has been maintained at 10 mg/L for 24 hours, drain the system. CT/EC water may be safely drained to the sanitary sewer. Municipal water and sewerage authorities should be contacted regarding local regulations. If a sanitary sewer is not available, consult local or state authorities (eg, Department of Natural Resources) regarding disposal of water. If necessary, the drain-off may be dechlorinated by dissipation or chemical neutralization with sodium bisulfite.
G. Refill system with water and repeat procedure outlined in steps 2-6 in I-B above.
III. Mechanical Cleaning
A. After water from the second chemical disinfection has been drained, shut down the CT/EC.
B. Inspect all water contact areas for sediment, sludge, and scale. Using brushes and/or a low-pressure water hose, thoroughly clean all CT/EC water contact areas including basin, sump, fill, spray nozzles, and fittings. Replace components as needed.
C. If possible, clean CT/EC water contact areas within the chillers.
IV. After Mechanical Cleaning
A. Fill the system with water, and add chlorine to achieve FRC level of 10 mg/L.
B. Circulate water for one hour, then open blowdown valve and flush the entire system until the water is free of turbidity.
C. Drain the system.
D. Open any air intake vents that were closed prior to cleaning.
E. Fill the system with water. CT/EC may be put back into service using an effective water-treatment program.
* Use of product names is for identification only and does not imply endorsement by the Public Health Service or the U.S. Department of Health and Human Services.
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Very Informative...
Dave,
In my experience with potable systems and cooling towers, this stuff is dead-on the mark.
We used to chlorinate our cooling tower (1.6 MG) twice per week...running the residual past 2.0 ppm and maintaining it above 1.5 for eight hours. While it was mainly for algae control, it kept all the other buggies at bay...too bad we never tested for Legionella. This thing put 100,000 gallons into the near environment on a busy day, so I wonder what effect it had...
I have always been concerned with the potable end...since you have the "hot" covered very well, I'll just mention the cold :-)
I am concerned with these large new houses that are well-fed for their domestic. Since only a very small percentage of these type of systems use chlorine - with the associated residual - my biggest concern are the ones with no disinfection...or UV lights.
Here's an example; family is away all day...Johnny arrives home from school and gets a drink or washes his face from the sink that hasn't been used since the day before. Doesn't that worry you? How about if that sink hasn't been used for two days...a week?
I have a UV light on my well system...no residual in my pipes. Because of this, part of my morning routine is to run the two faucets my family will use in the morning for about thirty seconds...this is the only reason to dump water IMHO (when it's going to be ingested in a non-residual system with significant "down" time)...if I need to water the plants, there's my source.
The other side of the coin with Cl2 (as mentioned in the article) is the bad effects of residuals as far as reacting with organics (THM's - trihalomethanes...a carcinogen) and other items. While this is a concern, it can easily be rectified by the use of carbon filters at the source. Just make sure you change the filters when required.
The one thing I have also wondered about but never see mentioned is pools. Combine these items...80F body of water, low Cl2 residuals (less than 0.2 ppm), bodily fluids being released (no need to get more specific is there?), and kids getting significant amounts of this water in their mouths...
For community pools, they are normally required to test for coliform once per week. If there's problems, there are protocols for shock treatment/etc. As far as I know, there is no required testing for Giardia, Legionella, etc...Dave, is there any references/worries about pools? Maybe the sun exposure makes a difference, due to UV rays?
Take Care, PJO0 -
pools & spas
The list of nasties expands for pools, but isn't typically a blip on the radar screen if chemistry is followed. Spas are a whole different ball game due to their elevated temps and chemistry that changes rapidly due to the higher temps and ratio of bodies to water volume - kind of like having 600 people in a standard size pool at the same time. Fecal matter, skin cells, soaps, deoderants, perfumes, etc... all provide food for bugs.
Here's an article I wrote for Smart Homeowner Magazine on this subject:
Bacteria Stew and the Hot Tub Goo
Like most people who get a hot tub, I gave little thought to bacterial issues and water quality monitoring received but a passing nod. The literature regarding our Ozinator led me to believe that it and the additional self-metering built-in Bromine tablet dispenser were all that I needed to have a perpetually fresh and sanitary oasis awaiting my aching bones. Large enough to accommodate six comfortably, we reveled in soaking under snowy skies while rushing waters rinsed away the days harried pace. Following the Midnight Christmas service, we would rush home to soak and listen to the plaintive wail of the steam whistle in downtown York playing Christmas carols.
But then it started: the odors began to subtly irk my subconscious; foaming along the edges took on a life of its own; chemicals were added; pH tests became a daily occurrence and still - I had a nagging feeling something wasnt right. As a Master Plumber, I should have known better and I started to think this through with the basic logic that makes up so much of what we do in my trade.
First of all, this aint your Mommas pool! Id assumed a hot tub was no different than a pool, but when you compare the volume of water between the two as it relates to body mass, youd need to have about six hundred people using your pool while it only takes two to approximate the same ratio in a hot tub. If youve ever had six hundred kids in your pool, youll already know what havoc that wreaks on the chemical balance. Theres also the temperature difference that doubles the chemical reactions for every ten degrees F increase.
And there are good reasons why just two bodies can create rapid chemical changes within the hot tubs environment. Were covered with residual soaps; perfumes; deodorants; dead skin; loose hair; and we sweat in hot water! As much sweating as with any strenuous work out, which is also one reason why times in hot water should be limited. Hard to believe you can get dehydrated while soaking in water, eh? But, theres the butt thing too. What you sit on becomes washed while luxuriating in the hot tub. Best to be real good friends! Funny how the sign at the pool requests you shower first, but we all plunk our butts into a hot tub without a second thought. Id mention the nose snot thing and other bodily fluids too, but youre likely to be grossed out enough already. Did I mention toe jam?
What are all the dead skin, sweat, and bodily fluids going to do for a hot tub environment? Give rise to potential bacterial growth. If you ignore simple routine maintenance, youll be setting up a bacteria stew that feeds upon the hot tub goo. Theres that legionella thing again and this time, were providing the ideal temperature ranges too. With fecal matter, theres the matter of Cryptosporidium, Giardia, E coli, and Shigella. Rounding up our basic intro to bacteria is Pseudomonas Aeruginosa, a bacterium that revels in hot tub environs, which typically results in skin rashes and can be deadly in rare cases.
Changing the water somehow seems somehow foreign, but the formula goes like this: No more than 30 days between water changes or divide 1/3 of the volume by the number of daily users to arrive at the frequency of complete water changes. Filters must be changed - no less than twice a year & preferably more often. Harsh cleaning with pressure washers or chemicals can destroy good filter performance. If you start out on a daily monitoring program and avail yourself of classes gladly taught by local hot tub dealers, you can easily avoid the bacterial stew and hot tub goo.
Then there are those hotel whirlpool tubs whose distribution piping and pump hold remnants from the previous occupants. Honey, did you remember to pack that gallon of Clorox?
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Hot Tubs...
Dave,
Great little piece on hot tubs - I like the title!
We got a hot tub last November, and it's great...especially when it's cold outside. I check the pH and Cl2 residual about twice a week because it isn't used every night. On the occasional heavy use I have adjusted accordingly...a small shot of disinfectant beforehand (especially if it's a bunch of kids!), and then test it and usually another shot afterwards. The pH only needs an occasional adjustment.
One thing about hot tubs that differs from other water treatment is that they seem to like the water a bit on the "hard" side (Ca and Mg). My water seems very well suited for this...varies between 90 and 120 ppm total hardness. I believe it has to do with the buffering, but maybe some tech in this field has a better clue?
To keep the bugs "confused", I setback the temperature about ten degrees when it's not in use. The manual says it is wasteful to do that, but I personally disagree...a lower delta T from tub to outside for 23 1/2 hours a day can't be wasteful, then it's twenty minutes to ramp up again. From what I've seen, the tub takes between 4 and 8 hours to get down to 92F after use. If I skip a day in the tub, then it stays at 92F for almost 48 hours.
My thinking is that at 92F there's a different population of bugs than at 102F...plus the chemicals are not as volatile from what I've read, and tend to stay around longer. The fairly quick increase to 102/104F doesn't make them happy either...wish I had it tied to my boiler, but I'll wait until the warranty is expired (right now it's a 6kW heater tied to my off-peak electric meter).
Any thoughts/comments on this setback and how it relates to the buggies?
Take care, PJO0 -
bugs
Wow, lot's of great info. I used to chlorinate towers before working on them after I got sick once changing vibration switches. Some customers cut way back on maint. I told my boss too bad, you want to do it?
I stopped using hotel spa's a long time ago. YUK!
Thanks
geno
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