Legionella: A Growing Problem
Understanding the problem of Legionella and how to prevent it plumbing systems.
You may have heard the term used in the news over the last few years, or maybe you skimmed over the word when digging through plumbing related literature. Maybe this has had no effect on you whatsoever and you are wondering what it has to do with you or what you could even do about it if it did. Nonetheless, Legionella is a hot topic in the plumbing industry right now, and there’s a lot yet to be decided when it comes to how the industry will react to the growing problem, Pun intended. My goal here is strictly to inform you of the research I have done because one thing is certain, change is coming.
So, what’s the problem?
The first major outbreak of Legionella occurred in Philadelphia in 1976 at an American Legion Convention, which is also where the name originates. Legionella is a rod-shaped, organic pathogen with more than 50 species, 18 of which can spread disease to humans. If inhaled into the lungs, Legionella can cause an infection with pneumonia-like symptoms. Legionnaires’ disease or the milder form, Pontiac fever, is typically contracted by breathing in the Legionella bacteria via water vapor. Known sources include, but are not limited to, hot tubs, wash fountains and cooling towers. Therefore, it’s a hazard that everyday people can contact in their homes and work, as well as on vacation like on cruise ships and within hotels. The microorganisms most commonly multiply in water at tepid temperatures with ideal temperatures being 68 F to 122 F, but it is also fairly resistant to lower temperatures and even chlorine. According to the Center for Disease Control (CDC), the disease affects 8,000-18,000 individuals annually. Prevention of Legionella growth in plumbing systems must be considered in all life stages of a building: design, installation and maintenance.
How is the industry addressing the problem?
The ANSI-approved ASHRAE 188 standard entitled “Legionellosis: Risk Management for Building Water Systems” was published in the summer of 2015. It is a consensus standard, which is anticipated to become the water management standard of care for non-residential building applications in future code editions. I should note that it is not currently referenced in the 2015 International Building Codes, but as recently as June 2016, the standard became a basis for a CDC toolkit. ASHRAE 12 standard (2000), “Minimizing the Risk of Legionellosis Associated with Building Water Systems” is simply a guideline and not a nationally adopted code requirement either, even though it’s been around for more than 15 years. This document will also undergo changes to align with 188. Here in lies a decision for all of us. It is not a code requirement, but turning a blind eye to the issue can cause major repercussions for engineers, contractors and building owners. After all, we are talking about human safety and the very definition of plumbing takes root in protection of life.
In 2015, after more than 100 people were infected and a dozen killed from a Legionella outbreak in New York City, the metropolis adopted section 7.2 of standard ANSI/ASHRAE 188 for risk management practices regarding cooling towers. The document takes a program approach to identify all system components with potential exposure to, as well as favorable conditions of, microbial bacteria progression. The publication also offers ways to mitigate the formation of such bacteria and describes contingency plans in the event of a positive test or inspection for organic matter.
What does this mean for you?
For engineers: Preliminary design phase elements to consider regarding Legionella growth prevention are water quality and piping materials. ASHRAE 188 does not address parameters of the water, and therefore, one must acknowledge the plumbing codes, related ASPE and ASHRAE guidelines, and consult with the local authorities having jurisdiction. Additionally, backflow preventers shall always be installed in accordance with local codes to protect the water supply from contamination by other sources, such as landscaping water.
As a general guideline, the standard level of chlorine in the water supply is typically 0.5 parts per million (ppm or mg/L). Scaling or corrosion of pipes can predispose systems to Legionella colonization due to the presence of biofilm, or groups of microorganisms. Therefore, it’s important to verify the water quality to determine if water treatment is required.
Piping materials also play a role as the bacterium can obtain nutrients from plastic and iron as stated on the EMSL Analytical Inc. website, which is a Legionella testing company. The International Plumbing Code (IPC) requires piping for use on the domestic water system to be third party-certified and labeled as such. Most piping will be labeled NSF 61 certified, but plastic pipes may also be labeled NSF 14 because that standard refers to NSF 61.
Flow and temperature are key water design parameters preventing bacteria growth. Well-designed systems allow proper scouring of pipes. When sizing the piping for a potable water system, velocities should be high enough to minimize the deposit of suspended material and to create friction within the pipe. If the piping is over-sized, the velocities are much lower and the pipe wall will not be scoured. The ideal velocities vary by piping material.
A typical water heater will produce and store 140 F hot water. The use of a master mixing valve will then mix the water down to 120 F for circulation, but also allow for provisions to flush the system with 140 F water. Additionally, most faucets and shower valves have point-of-use mixing valves creating 110 F water to prevent scalding. Recirculation helps to maintain the temperature in the system within 5 degrees and allows the water heater to operate more efficiently, due to the higher temperature of the water at the inlet.
For contractors: Throughout the installation phase, piping should be handled with care and capped when stored to prevent foreign matter entering the pipe, and all systems should be cleaned after construction or repair per sections 610.1 and 602.3.4 of the IPC. This eliminates deleterious matter within the piping system and disinfects the lines for use in accordance with AWWA C651 or AWWA C652, as referenced in the IPC, for disinfection of water mains and storage. The system must first be flushed with water, and then filled with either 50 mg/L of chlorine for 24 hours or 200 mg/L for three hours. Lastly, the concentrated chlorine must be purged with potable water.
For building owners: Regarding the maintenance and building ownership phase, there’s one definition in ANSI 188 that I would like to highlight. The word control is to “manage the conditions of an operation in order to maintain compliance with the established criteria.” The established criteria mentioned being the standard itself and related best practices, for now.
Building owners can complete a risk evaluation worksheet, obtain a basic management program model and review examples of typical responses to scenarios in which water treatment is required via the CDC toolkit found at www.cdc.gov/legionella. The plan model will identify key areas to maintain in order to prevent bacteria development. Things like un-used fixtures, branch piping and vessels storing water can harbor bacteria and should be purged periodically of stagnant water. One example is emergency shower fixtures, which should be tested, but are not used or naturally flushed on a regular basis. Showerheads and sink aerators should be removed to flush the fixture itself. A hot water system bypass can be used to circulate a minimum of 140 F water throughout the system. Legionella bacteria dies within approximately 32 minutes when exposed to 140 F water. Filters, hoses and ice machines fed from a cold-water source shall also be inspected and cleaned to prevent the same.
If Legionella is suspected, disinfection of the system is required. ANSI/ASHRAE 188 defines the measure of control to be disinfection via “heating ... filtering, flushing or other means [and] methods.” Another useful guideline provided by the American Society of Plumbing Engineers (ASPE) is Design Handbook Volume 4, which states “chlorination of water is most commonly used to destroy organic (living) impurities.” Disinfection is achieved by adding chlorine gas or hypochlorite solutions to the piping system. Chlorinators are available to automatically inject the water system with proportional amounts of chlorine gas. Additionally, third party industrial hygiene, testing and risk management firms can diagnose water treatment requirements and remedies. Companies with proper training on Legionella sampling can collect water from key areas within a buildings system and send to a qualified laboratory for evaluation to begin the process if waterborne bacteria activity is suspected.
When things start to affect our pocketbook, that’s when we begin caring. So, no matter who you are, I hope that you are better informed by this information in order to help spur the needed intrinsic look at plumbing systems and to become aware of the forthcoming changes to the building codes. The technical leaders in the industry are certainly focused on better control measures to lessen preventable cases and the spread of Legionnaires disease within existing and new infrastructure. This holistic approach lessens the need for governmental intervention which can take years to fund and implement, and is sometimes accompanied by tax hikes.
I would love to hear your comments on the matter and may even include them in a follow-up article down the road. Please email your comments to firstname.lastname@example.org.
Lyric Lain is the first certified plumbing designer at the employee-owned, design-build company Burns & McDonnell, which is located in Fort Worth, Texas. Lain has served on the Dallas-Fort Worth American Society of Plumbing Engineers (ASPE) Board of Directors as corresponding secretary and newsletter editor. With more than eight years in the plumbing-design industry, she is currently seeking her mechanical engineering degree.