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/ Solutions for thermostatic mixing valves

ABOUT LEGIONNAIRES' DISEASE

What is Legionnaires’ disease? Current curative treatments are ineffective
It is a serious respiratory infection caused - Chemical shocks: a chlorine injection 50 mg/L for
by a bacterium: Legionella. The illness which follows, 1 hour (HSE guidance); ≥ 10 mg/L for 8 hours (WHO).
Legionnaires' disease, is fatal in 15 20% - Thermal shocks: circulating hot water at 60°C
of cases. for 60 minutes (in Europe: 70°C for 30 minutes).
Legionella is a system bacterium which develops • A short term effect:
in warm water in pipework or cisterns. It only becomes The system can be very quickly recolonised
Hygiene and controlling
bacterial proliferation dangerous when inhaled when it may spread into within 3 4 weeks. The inside of the pipework
the lungs and rapidly develop in white blood cells. is covered by a biofilm: a sort of gel which bacteria
stick to, feed on and proliferate in.
Legionnaires' disease is more likely to affect adults, The biofilm protects them and enables them
especially older smokers and people with respiratory to withstand temperature variations (thermal shocks)
problems or weak immune systems. and biocide products (chemical shocks).
Chlorine
Legionnaires' disease is treated with antibiotics. During curative treatments, the risk is not only that
The World Health Organization (WHO) states that the bacteria will get used to the treatment and
the alert level for Legionella starts at 1,000 Colony thus develop their resistance to it, but above all will
Forming Units (CFU) per litre of water provoke detachment of bacteria aggregates which
(250 for hospitals). will be deposited closer to the water outlet and thus,
Chemical shocks are ineffective The UK alert level is 100 CFU/L. to the user.
over the long term
Which installations are at risk? • Negative effect in distribution networks
Legionellae develop in stagnant water between and drainage systems
25 45°C, with an optimum temperature between They are not necessarily designed to withstand
30 37°C. Humid areas with scale, mud or which temperatures above 60°C or significant quantities
70°C have been affected by corrosion are more prone to of chlorine. They can cause corrosion or premature
Legionella development.
ageing of the distribution and drainage system.
Environments at risk include hot water systems, • High risk for the user
cooling towers, health resorts, water fountains, During the treatment, the user is exposed to high risks:
rd
shower rooms, spas, etc. - 3 degree burns in the case of a thermal shock.
- Poisoning in the case of chemical shock treatment.
Thermal shocks are ineffective
over the long term Unknown contamination source
• Costly and difficult operation to undertake
58% Curative treatments are difficult to undertake fully
Hotels, 13% at all points in the system (various deposits, dead-
campsites legs, heat loss, etc.). They require the water supply
8% 6%
8% 4% to be out-of-service and the mobilisation
3% of maintenance staff.
Hospitals Temporary
residences
(lodging, B&Bs, To avoid these treatments it is important to act
Buildings open to the public Care homestay, etc.)
(swimming pools, stadiums, etc.) Homes on four levels:
- Avoid dead-legs and water stagnation.
Other types of trips
- Regularly maintain the system to prevent corrosion
or scaling.
Source: French Institute for Public Health Surveillance, 2015,
based on 1,389 declared cases - Produce and store hot water at a high temperature
that will prohibit bacterial proliferation.
- Maintain the temperature in the system
Development of Legionella per temperature
with a circulating loop and mix the water
as close as possible to the point-of-use.
Temperature Development of Legionella
< 20°C Dormant The only preventive treatments that are effective
in the long term are the ones recommended by
25 45°C Multiplies
the UK Health and Safety Executive (HSE) technical
guidance "HSG274 Part 2" in 2014.
50°C 90% die within 2 hours
60°C 90% die within 2 minutes
Source: CSTC Belgium November 2002

144 Thermostatic mixing valves