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PART 4: What should the owner of a comfort cooling tower do about the risk of Legionellosis?

admin — Thu, 17 Dec 2009 13:46:21 +0000

First, understand that the risk is real, and that facilities have a responsibility to create a strategy to minimize the risks of L. pneumophila proliferation. That strategy should focus on good operating practices, specifically with respect to maintaining good control of bacteria populations.

A little background about bacteria: There are two types of bacteria in cooling water: planktonic and sessile. Planktonic bacteria are free-floating in the bulk water and, even at relatively high populations, are invisible to the human eye. Sessile bacteria are immobile; they attach themselves to water-wetted surfaces and have a slippery texture, often described as “slime.”

The slime is comprised of extracellular polymeric substances (EPS) that envelops bacteria, including L. pneumophila, and acts as a barrier to the killing power of oxidizing biocides such as chlorine or bromine. Slime incubates bacteria, protecting it from biocides while allowing the bacteria to proliferate on the tube surfaces and inhibiting heat transfer in the chiller.

As the bacteria thrive, the thickness of the slime layer increases and starts to detach from the surface, spewing bacteria into the bulk water. Chemical suppliers have developed a variety of very expensive non-oxidizing biocides that can penetrate the slime layer and kill the bacteria.

The common bacteria test, a “dip slide,” measures the population of planktonic bacteria by using an agar-coated paddle “dipped” into a fresh sample of cooling water and incubated for 24 – 36 hours at a controlled temperature. Users then visually compare the pattern of the dye-stained bacteria on the paddle to the reference photographs and estimate the bacteria population. However, by the time the dip slide test detects detached sessile bacteria, the risk of bacteria escaping in water droplets in the vapor plume has escalated dramatically.

There are few field tests for sessile bacteria; most chemical suppliers measure only planktonic bacteria, not sessile bacteria. Therefore, the most pragmatic method of controlling sessile bacteria is to maintain continuous control of planktonic bacteria populations by feeding oxidiaing and non-oxidizing biocides at the rates recommended by the chemical supplier.

Some technicians use a quantitative method of evaluating slime by periodically swabbing the surface of a corrosion test coupon, or swabbing a stainless steel mesh coupon in the first position in the bypass coupon rack. Technicians can get a semi-quantitative measurement by dissolving the material on the swab in distilled water and using a dip slide to measure the formerly-sessile-now-planktonic bacteria population.

Some of my clients have asked me whether there’s any value to directly measure the population of L. pneumophila bacteria in the cooling water. The short answer is No. The longer answer is: direct measurement of L. pneumophila bacteria could actually result in mis-interpretation of the risk and an over-reaction, implementing corrective actions that have little positive value and could cause high corrosion rates.

Remember, the population of L. pneumophila bacteria is just one of three factors that result in a risk of infection. And it’s impossible to correlate a single measurement of L. pneumophila bacteria with risk of infection.

However, some facility managers may determine that direct testing for L. pneumophila bacteria is appropriate. If a facility manager wants a direct measurement of the L. pneumophila bacteria, the classic method requires mailing a water sample to a laboratory for culturing and bacteria identification, a process that takes 3 to 14 days to get results.

There are two technologies for field measurements of bacteria; direct fluorescence antibody (DFA) and a polymerase chain reaction (PCR) method that employs nucleic acid-based amplification. The DFA test method cannot discriminate between live and dead bacteria, while the PCR method is so new that correlation to classic culture method is not well-documented.

What the industry is doing about the risk of Legionellosis from cooling towers

admin — Fri, 04 Dec 2009 18:52:26 +0000

Industry is addressing this issue from two perspectives: providing guidance for best practices, and developing new products.

In 2000, the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) released a set of best practices for facility managers, Guideline 12 -2000, Minimizing the Risk of Legionellosis Associated with Building Water Systems. (http://www.ashrae.org)

The guideline has proven to be an excellent set of best practices for cooling tower owners. However, the guideline has one major deficiency: it can’t help facility managers assess the magnitude of the risk of L. pneumophila infection from their cooling towers.
The solution to risk assessment is the creation of a standard, SPC 188, modeled after the food industry’s Hazard Analysis and Critical Control Points (HACCP) methodology. The HACCP approach requires establishing teams to evaluate a facility’s equipment and operating practices to rate and rank the risks of L. pneumophila proliferation. Auditors devise customized sets of critical control points and operating practices to control the hazard of L. pneumophila proliferation, document a monitoring plan to confirm control of the hazards, and validate that facility personnel are implementing this HACCP process.
The release date of the standard is unknown, but the standards committee has been working for nearly three years to craft the document.
The industry is developing new products in several areas. Most importantly is the development of highly efficient drift eliminators that are critical to reducing the dispersion of water droplets with the cooling tower plume. Other improvements include additional field tests for bacteria, including legionella, new biocide formulations, and improved chemical feed and control systems.
Watch for Post #4 in this 4-part posting, “What should a tower owner do about it?”
copyright 2009 MarTech Systems, Inc.

Calculating the cost of doing nothing

admin — Tue, 10 Nov 2009 16:42:10 +0000

Some time ago, a client called me from his company’s corporate jet. This was not a good sign; energy managers are not supposed to be on corporate jets. One of their refineries had shutdown; the press release mentioned the cause as “electrical power and steam supply.” Uh oh. When the word “water” or “steam” or “condensate” appears in a press release, there’s trouble. And, perhaps, there’s opportunity.

Like many refineries, this site has an aging water utility system. The lack of maintenance and, in some cases, lack of replacement of equipment, has resulted in extraordinarily high operator effort (e. g. manual operations, no on-line analyzers to collect data and inconsistent operation). In short, these operators are being asked to work miracles.

In an effort to maintain control of the process, operators accommodate the limitations of the system by operating very cautiously and conservatively; this strategy translates into increased operating costs. Systems continue to deteriorate, safety margins increase and one day, during peak demand or unusual operating dynamics, the water utility system cannot meet the plant’s requirements.

In better economic times, refiners would just throw money at the problem (e.g. buy equipment) to solve the problem. But refineries are currently operating with little or no profit, and even if capital funding were available, it’s a long and difficult process to justify expenditures in a low-ROI water utility system.

The next option is operating funds. But refiners have dramatically cut their operating budgets, idled units and laid-off employees. Adding to the challenge of justifying operating funds is the complexity of most operating problems. The root cause of most operating problems is a combination of equipment limitations and operator focus and expertise. The typical response to a problem is to demand a higher level of operator attention. But it’s naïve to expect that operators can solve these complex problems without some equipment improvement.

So what’s the solution? Here’s my starting point: calculate the cost of doing nothing: Doing nothing guarantees that problems will re-occur and escalate in severity.

Next, assemble everyone affected by water and clarify the goal. Everyone: Operations (operators and process engineers), Tech Service, Maintenance, Reliability.

Here’s a sample goal for a malfunctioning pretreatment system: To reliably produce boiler make-up water that meets the specification 99% of the time.

Lastly, get down to business: confirm philosophy (e.g. outsourcing is viewed as risky because….), identify hurdles (e.g. it will take an ROI of X% to get a capital project approved) and short, medium and long term goals (e.g. make operational changes immediately, make instrumentation changes within the next six months to increase the volume of data for monitoring, conduct a water use audit to avoid wasting water), assign responsibilities and gain agreement on performance metrics and schedules.

How do I know that this strategy works? In a word, experience. I have walked through the valley of death when my client’s flagship refinery had a failure in the centralized pretreatment system, shutting down the entire refinery. We slowly, painfully recovered from chaos and disaster and worked our way back to competency and control. Along the way, we learned what went wrong and changed the culture to prevent similar problems from occurring again.

PART 2: Is the risk of Legionellosis from my cooling tower real?

admin — Tue, 10 Nov 2009 16:35:43 +0000

Yes, it’s real. Your cooling tower could cause Legionellosis infections. Since the first confirmed outbreak at the American Legion convention at the Bellevue Stratford Hotel in Philadelphia in 1976, the Centers for Disease Control and Prevention (CDC, http://www.cdc.gov) has documented thousands of cases. Documenting the source of the bacteria can be difficult, but the CDC has confirmed cooling towers as the source of numerous infections.

The CDC has identified both commercial and industrial cooling towers as sources of infection, also known as “community-acquired infections.” In several instances, industrial cooling towers disseminated aerosolized L. pneumophila to a distance of at least one mile, and perhaps as far as two miles.

Comfort cooling towers are not as large as industrial cooling towers, but often they are located on the top of multi-storied office buildings. This elevation of the tower increases the size of the drift zone and may include the ventilation system’s air intakes for adjacent buildings – creating a risk of exposure to infected water droplets for occupants of nearby buildings. The drift may reach ground level several hundred or several thousand yards from the building, placing individuals who live or work in the surrounding neighborhood at risk of exposure to infected water droplets.

This transport of bacteria beyond the boundary limits of the building increases the responsibility of cooling tower operators to properly manage the bacteria populations.

Consider this scary thought: the first indication that your cooling tower is a source of infection might be an outbreak in a nearby building or the local community, not an infection of an occupant of your building.

Here’s another sobering thought: according to the CDC, each year, between 8,000 and 18,000 people are hospitalized with Legionnaires’ disease in the United States, but health authorities suspect that many infections are not diagnosed or reported.

Finally, we know that Legionnaires’ disease can be fatal – a CDC study of reported cases indicated a death rate of 20 percent for community-acquired cases.

PART 3: Watch for post #3 in this 4-part posting, “What the industry is doing about the risk”
copyright 2009 MarTech Systems, Inc.

PART 1: Could your cooling tower get you in hot water?

admin — Thu, 05 Nov 2009 14:31:47 +0000

Some questions merit long answers. The risk of Legionellosis infections from a cooling tower is one of those questions. I invite you to tune in on a weekly basis as I continue this special 4-part blog.

Here in the Northeast U.S., it’s “shoulder season” for comfort cooling towers. Cool days interrupted by an occasional hot day, cause chillers and the matched cooling towers to operate very intermittently. Soon facility managers will drain these seasonally-operated towers. But until winter weather requires tower shutdown, these long, idle periods make me worry about the risk of bacteria growth in the stagnant water that is trapped in the system.

Why do I worry about the risk of bacteria growth in stagnant water? legionella bacteria

Admittedly, legionella bacteria are ubiquitous in natural waters and in cooling towers. In a recent study, Richard Miller, Environmental Safety Technologies, Inc. (http://www.estechlab.com), found that 13% of 2599 samples from comfort cooling systems contained legionella pneumophila (L. pneumophila) bacteria. The specific strain that causes the disease, Legionellosis, or its milder form, Pontiac Fever, is L. pneumophila sero group 1.

The first factor, the presence of this bacterium in cooling water, isn’t dangerous by itself. The bacteria in the cooling water must be delivered into a person’s lungs; a person must breathe-in droplets of “infected” cooling water.

How do infected water droplets leave the tower and reach a person’s lungs? The tower has drift eliminators to minimize entrainment of water droplets in the evaporated water or plume exiting out of the top of the tower. But damaged drift eliminators and/or excessively high fan speeds allow infected water droplets to leave the tower with the plume.

The second factor is exposure. People who live or work in the area of the cooling tower plume are at risk of inhaling entrained water droplets.

The third factor that contributes to the risk of infection is the health of the person breathing these “contaminated” water droplets into their lungs. Persons with poor immune system function or compromised breathing are at a very high risk: transplant recipients; smokers; chronically ill and people with lung disease.

So at this time of year, take a look at the bacteria population of the cooling water, the location of the plume, and whether your tower is near a community of people who could be vulnerable to infection with the L. pnuemophila bacteria.

Watch for post #2 in this 4-part posting, “Is the risk real?”

The Importance of Data

admin — Wed, 04 Nov 2009 19:17:28 +0000

For the last decade, as the “Water Doctor” for a chemical plant on the Gulf Coast, I’ve watched management’s slow progress gaining cooperation of operators to enter data into the centralized electronic database.

My experience at this plant prompted me to discuss the need for a robust data collection and management system in my November 2009 column, Are your decisions based on obtained data? Hydrocarbon Processing, Gulf Publishing, Inc..

Here’s an excerpt – see how your plant measures up.

Take this short quiz…give your plant one point for each “True” answer.

The plant log sheets show specification limits.
Operators or central lab are responsible for validating accuracy of non-conforming test results.
All data are logged into an electronic database.
The operator or central lab chemist enters data into the database and validates the accuracy of the data.
All electronic data are stored on a server and accessible to all plant personnel.
Critical data are automatically tabulated into trend graphs in the centralized database.
The plant engineers have identified key performance indices (KPI’s) and key operating indices (KOI’s).
The plant engineers tabulate compliance statistics for KOI and KPI data.
The operations and tech-service personnel are trained to modify trend graphs and to conduct statistical analyses on the data.
Operations and tech-service personnel regularly review the data and use it to troubleshoot and to optimize operations.

I won’t keep you guessing; that Gulf Coast chemical plant that I mentioned scored a 5 on the quiz; we still have a lot of work to do.

To read the complete article, visit http://www.martechsystems.com/columns.html/