Cooling Tower Safety and Maintenance
In 2001, a major worldwide automobile manufacturer experienced a tragedy when four maintenance employees at one facility became ill with pneumonia-like symptoms that ultimately claimed the lives of two. The cause: Legionnaires' disease, caused by the Legionella bacteria found in one of the automaker's process cooling towers. The company quickly moved to conduct a cause analysis by inspecting its cooling towers worldwide to identify how systems were being maintained and to determine best maintenance practices. This ultimately led to the establishment of a world-class monitoring and maintenance procedure that ensures such a tragedy will never be repeated at the company.
Interestingly, when someone becomes ill from an unsafe cooling tower, it most often is not the result of a company's blatant negligence. Rather, it is typically the result of a company not having a clear understanding of the need for its water treatment program to be in alignment with an effective debris-management and cooling tower maintenance program. While it may seem obvious that if the amount of debris inside a cooling tower exceeds the established biocide dosage, the demand placed on the dosage will be consumed quickly and will have little impact on the bioactivity. In other words, the debris and bioactivity occurring in a cooling tower can overwhelm the chemical dosage. It is important to remember that cooling towers are highly efficient air scrubbers; anything drifting past a cooling tower is likely to get caught in its draft and be sucked in.
What should the ratio of water treatment chemicals to debris load inside the cooling tower be to ensure cooling tower safety? Organic debris is drawn into cooling towers in different concentrations depending on location and time of year. Every type of debris places a different demand on the biocides and scale inhibitors being dosed into the water; therefore, there is no known ratio that will hold constant for every cooling tower. However, if you do not deploy diligent maintenance procedures that specifically call for the prevention of organic debris getting into the cooling tower or its periodic removal, more water treatment chemicals will be required to keep it safe. Some may say to load the tower up with chemicals to ensure safety. However, federal and state Environmental Protection Agency (EPA) guidelines place restrictions on the amount and type of chemicals that can be used; therefore, the use of chemical treatment alone may not be adequate.
Furthermore, adding chemicals to offset poor maintenance practices is a shortcut that will do little to prevent fouling and clogging of the fill, strainers, blowdown valves, chiller and heat exchangers. In addition, this practice could lead to health and safety problems and a reduction in equipment performance. The safest recommendation is to keep the cooling tower free of debris and deploy a good water treatment program, and your cooling tower will operate safely and efficiently. This may sound like an oversimplification, but if you keep the debris out of the cooling tower, you will break the bacteria-
supporting food chain. Additionally, when you chemically treat the water, you create an environment non-conducive to bacteria habitation. In short, when you eliminate food and shelter for bacteria, it will not take up residence in your cooling tower.
Keeping a Safe Cooling TowerIn recent years, the American Society for Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) has established excellent recommendations for cooling tower maintenance, known as Guideline 12. In addition to recommending maintenance activities, it calls for establishing procedures that are measurable. Although ASHRAE guidelines are excellent, companies ultimately must weigh the operational and economic realities of any maintenance procedure they deploy. As the old cliché goes, "There's more than one way to skin a cat." If maintenance procedures are too frequent, cumbersome or complex, more downtime, lost productivity and higher maintenance costs may result. Also, natural human tendency is to take shortcuts to complete an unpleasant job quickly, often with unsatisfactory results. Conversely, if the intervals between maintenance are too long, it may be more cost effective, but the condition of the cooling tower at each interval may be less than desirable and potentially place maintenance workers, employees, tenants and the public at risk. So, the answer largely lies somewhere in the middle, where water treatment and managing debris in the tower come together.
Companies have many options for managing debris, including water-based and air-intake filtration technologies. Water filtration can help manage waterborne and other debris in the cooling water; air-intake filtration technology can stop airborne debris from getting into the tower. Air-intake filtration also can be used in glycol-based cooling systems and on other air-cooled condenser systems to keep airborne debris out of the coils.
When determining what maintenance and debris management technology to use, it is important to first determine the source of debris. If the source is waterborne (e.g., sediment, algae from pond or river, or water with high dissolved solids content), water filtration, in combination with a good water treatment program, will protect the chiller and heat exchanger from scaling and fouling. If the source of debris is airborne (e.g., cottonwood seed, insects, leaves, pine needles, paper, birds and droppings, harvest chaff, construction debris), air-intake filtration, which filters the air as it enters the system, will prevent the debris from getting into the system. Air-intake filtration, in combination with a good water treatment program, is effective in stopping the kind of debris that clogs strainers, blowdown valves, cooling tower fill, chillers and heat exchangers. In cases where both waterborne and airborne debris are problematic, both air-intake and water filtration, in combination with a good water treatment program, may be required to keep the cooling tower safe and operating efficiently.
Personnel SafetyNo matter what procedures are adopted in maintaining cooling towers, personnel safety precautions are integral to maintenance procedures. Best practices require workers to wear respirators, gloves and protective clothing to help prevent exposure to bacteria, especially Legionella. Cooling water does not have to look dirty to be dangerous. Just because the water is clear does not mean it is clean or free of bacteria. Every cooling tower can harbor bacteria. Always take precautions because unless the water is routinely tested for Legionella and other bacteria, the bacteria will never announce its presence until it is too late.
Companies that do not take appropriate precautions and do not insist upon diligent cooling tower maintenance procedures put not only their employees' health and safety at risk, but also their businesses and reputations. Consider the consequences of a single cooling-tower-related Legionella incident:
- Reduced employee moral and productivity due to an unsafe work environment.
- Negative customer perceptions of the company and reduced customer willingness to buy goods and services should a Legionella outbreak become public. (This is especially risky for food and food-related processors.)
- Loss of income to families when a loved one becomes ill or dies from Legionella.
- High cost for litigation that can follow an incident.
- Higher company insurance costs when claims due to job-related sickness or death occur.
In comparison to the cost of a proactive maintenance initiative, the incidents listed above, considered individually or collectively, carry staggering costs.
Learn from a Leader's MistakeHow did the major automotive company manage to take a tragic situation and turn it into a world-class maintenance program? The company formed an oversight committee sponsored by executive management that was charged with the responsibility of working with consultants, water-treatment professionals and maintenance employees to establish a global water-management program. This program encompasses specific maintenance tasks, methods and schedules; management accountabilities; and reporting guidelines at the facility level. The representative at each facility is accountable to a regional representative, who reports activities and results to the oversight committee. The establishment of the oversight committee and its global management network ensures uniformity of its program. It also gives the company a vehicle to quickly implement changes and enhancements that provide continuous improvement to its global water-management program.
When it comes to ensuring the health and safety of employees and facilities, it does not take rocket science; it just requires companies to "step up to the plate" and initiate proactive, ongoing maintenance procedures that align effective debris-management technology with water testing and treatment techniques. When these elements are in alignment, the result is a safe, healthy and efficient operation.