The fight against Legionella

How keeping Legionella out of water systems can reduce the risk of infection.


The first major outbreak of Legionnaires’ Disease occurred in July of 1976 at an American Legion convention in Philadelphia at the Bellevue-Stratford Hotel. The source of the outbreak was cooling tower water infected with high concentrations of Legionella that became airborne on wind currents. The airborne bacteria were inhaled by a number of convention participants. In the end, 130 convention attendees were hospitalized with pneumonia-like symptoms, resulting in 25 fatalities.

Last year, the Centers for Disease Control and Prevention estimated that between 8,000 and 18,000 people were hospitalized with Legionnaires’ Disease, which is caused by exposure to Legionella Pneumophilia (CDC, 2013). Legionnaires’ Disease can be a fatal form of pneumonia acquired by inhaling the Legionella bacteria through the lungs. The bacteria is not spread from person to person and is naturally found in the environment including cooling towers, decorative fountains, evaporative condensers, hot tubs, and hot water systems. The key to reducing the risk of infection is keeping Legionella out of water systems.

By November of 1976, The Bellevue-Stratford, one of Philadelphia’s premier hotels, closed their doors for good. Legionella Pneumophilia are dormant at temperatures ranging from 0˚ F. to 68˚ F. At temperatures ranging between 68˚F to 121˚ F., Legionella thrive and multiply. At temperature above 121˚F, Legionella are killed within the following time frame: 100% are instantly killed at 160˚ F.; 90% are killed within 2 minutes at 140˚ F.; 90% are killed within 2 hours at 122˚ F. Legionella also thrive in environments rich with nutrients such as algae, flavobacteria, pseudomonas, biofilms, and scales that can be found in hot water tanks and dead legs in domestic hot water systems.

Water testing and emergency disinfection

The key to determining the present risk of Legionella infection is regular and routine water testing. Water samples from different areas of the domestic hot water system should be sent to a qualified laboratory for analysis. A Legionella mitigation strategy should be formed based on the results of regular water testing. Assuming that a significant Legionella Colony Forming Unit (CFU) exists within a domestic hot water system, steps must be taken to eradicate and disinfect the system.

There are two recommended types of methods for emergency disinfection; Hyper Halogenation and Thermal Eradication. Hyper Halogenation involves isolating the infected water side piping system and introducing high levels of a halogen that kill waterborne organisms. Once the hyper halogenation process is complete, the piping must be flushed and water samples must be taken at different locations to ensure that concentrations of the halogen are below safe drinking water levels.

High concentration levels of halogens, however, can be destructive to piping and fixtures. Damage to water systems from halogens can be expensive. Furthermore, high concentrations of halogens are not altogether reliable due to the ineffectiveness in penetrating bio films.

Another method for emergency disinfection is Thermal Eradication. This method requires the isolation of the water side piping system and increasing the hot water system temperature to greater than 160˚ F. While circulation of this extreme hot water continues throughout the system, each distal tap is then flushed by an operator for a pre-determined period of time.

Domestic hot water heaters must have the ability to generate these high temperatures in an emergency disinfection mode without the interference of temperature safety systems at a prescribed flow rate suitable for system coverage. Once the thermal eradication process is complete, water system temperatures must be returned to safe levels before the water system is recommissioned. Once the water system is disinfected, routine water treatment maintenance must continue.

One way of treatment is silver copper ionization. Positively charged silver and copper ions are introduced into the water system that attach themselves to the negatively charged Legionella organisms causing cell death. This is a highly effective treatment process but concentrated levels of heavy metals can be toxic to humans so regular testing for unsafe levels of heavy metals is recommended.

Another form of treatment is ultraviolet light. Exposure of the domestic water flow to an ultraviolet light source (254nM) renders the suspended Legionella bacteria unable to reproduce. Pre-filtration is essential with this highly effective treatment method as wavelengths can be distorted by the presence of debris on the light source. Unless the water flows past the UV light source, however, it will remain untreated.

Hyperchlorinization is another method for water treatment. This method introduces higher levels of chlorine into water systems while keeping below safe drinking water standards. As stated earlier, chlorine can be destructive to water systems and is not always effective as higher Legionella CFUs can avoid exposure through biofilms with some strains showing resistance to chlorine contact. Chlorine also decays at higher temperatures.

Finally, the heat treatment method involves increasing the outlet water temperature of domestic hot water heating systems to temperatures above a 140˚ F. Of course scalding is a danger and so the hot water must be tempered with cooler water before usage. However, Legionella growth can be limited as long as system temperatures remain above the Legionella “kill zone.” This method is perhaps the most cost effective as hot water is already created and is not non-toxic and not destructive to piping systems.

- Content provided by Spirax Sarco, originally published in Steam News Magazine.

- Edited by Jessica DuBois-Maahs, Associate Content Manager, CFE Media, Plant Engineering, Control Engineering

The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
Pipe fabrication and IIoT; 2017 Product of the Year finalists
The future of electrical safety; Four keys to RPM success; Picking the right weld fume option
A new approach to the Skills Gap; Community colleges may hold the key for manufacturing; 2017 Engineering Leaders Under 40
Control room technology innovation; Practical approaches to corrosion protection; Pipeline regulator revises quality programs
The cloud, mobility, and remote operations; SCADA and contextual mobility; Custom UPS empowering a secure pipeline
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Power system design for high-performance buildings; mitigating arc flash hazards
VFDs improving motion control applications; Powering automation and IIoT wirelessly; Connecting the dots
Natural gas engines; New applications for fuel cells; Large engines become more efficient; Extending boiler life

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
The maintenance journey has been a long, slow trek for most manufacturers and has gone from preventive maintenance to predictive maintenance.
This digital report explains how plant engineers and subject matter experts (SME) need support for time series data and its many challenges.
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.
Maintenance Manager; California Oils Corp.
Associate, Electrical Engineering; Wood Harbinger
Control Systems Engineer; Robert Bosch Corp.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me