1. Legionella & Backflow
Kelvin Slade
Chair

2. THE BIG QUESTION’S

3. THE BIG QUESTION’S
Can backflow prevention assist in preventing a Legionella (Legionellosis) outbreak?

4. THE BIG QUESTION’S
Can backflow prevention assist in preventing a Legionella (Legionellosis) outbreak?
Can backflow prevention promote a Legionella outbreak?

5. THE BIG QUESTION’S
Can backflow prevention assist in preventing a Legionella (Legionellosis) outbreak? – YES
Can backflow prevention promote a Legionella outbreak? - YES

6. HOW SO ?
We need to consider the characteristics of backflow prevention and the Legionella bacteria
Independently

7. Backflow Terminology Basics
Back-siphonage:
Backflow that occurs when the water supply pressure falls below atmospheric pressure = kPa (at sea level)
Backflow:
1) Flow in a direction contrary to the normal or intended direction of flow.
2) The unintended flow of water from a potentially polluted source into a potable water supply.

8. Legionella – The Recipe
Water quality, sediment = biofilm
The bacteria exists naturally but is dormant <200C
Water temperature >250C - <500C (350 – 460)
Low flow rates & infrequently used branch lines
Pipe material & age
Low residual chlorine, ppm (Qld Health Guidelines)
Outbreaks can be seasonal, dependent on ambient temperature

9. AS3500.1:2015 Sect 4 Protection Of Water Supplies
Cl Design – All water supply systems shall be designed, installed and maintained so as to prevent contaminants from being introduced into the drinking water supply system.

10. The problem is, the contaminate is already in the water supply before in enters property.
The job at hand is to design and install our backflow prevention installations in a manner that does not promote legionella growth.

13. BIOFILM
Aerator
TMV Strainer

15. Produced by The European Working Group For Legionella Infections ESGLI

16. Some notable points: Risk assessments –
1.15  The risk of legionellosis associated with a water system or piece of equipment utilising water is dependent on its design, installation, commissioning, operation, management and maintenance. The more complex the system, the greater the likelihood of colonisation either within the system or within areas and/or components in, or attached to, the system.

17. Risk Assessment Cont
1.17 The risk of legionellosis is present when:
there are conditions suitable for microbial growth to levels which may cause infection, for example:
a suitable temperature for growth (20°C to 45°C),
poor or no flow,
where there may be ingress from cross-connections especially during maintenance,
where there is inadequate backflow protection,
where there are inappropriate materials providing a source of nutrients for growth and biofilm formation including sludge, scale, rust, algae and other organic matter,

18. Hot & Cold Water System considerations

19. The USA haven't got it right either!
A comment from the CDC
“I must warn you that the US is probably behind Europe and Australia as far as legislation goes.”
“However, much of the enforcement is accomplished after the fact through litigation. I know. Not the best system for prevention. We’re working on it!”

20. A point for discussion Bypass assembly design
Three ingredients - Low flow rates.
- Infrequently used used branch lines.
- Stagnant water temperature
The bypass branch (tee) connecting a containment bypass assembly could be a very real risk in biofilm accumulation.
Dead legs are a major issue, UK guidelines = any infrequently used branch longer than 1.5 x diameter of the main distribution pipe they are taken from should be avoided.

21. 3500.1:2015. Sec 4
Cl General - Note 1. In assessing a backflow condition, consideration should be given to the complexity of piping, the probability of piping change, and incorrect use of equipment resulting in a backflow condition.
Cl General Installation requirements
The installation of each backflow prevention device shall comply with the following requirements:
(i) Where continuous water supply is essential, devices shall be installed in parallel to permit shutdown of a device.

22. A Legionella risk downstream of the bypass??
Containment Backflow Assembly
Configuration not recommended

23. Preferred configuration

24. Mitigating the Legionella growth risk
Water risk management is a complex issue
There is no silver bullet in Legionella prevention
Designers and installers have a part to play in risk mitigation

25. Take Home Points Water Risk Management is evolving world wide
Understanding the ecology of Legionella Pneumophila is complex, considering there are over 330 strains of Legionella Sero Group 1
Legionella bacteria growth can occur in as little as 12 hrs – generally hrs
Backflow Prevention has a part to play in water safety, Lets stay on top of it
Education and awareness is key

26. Happy Healthy Plumbing !