Page 147 - Water_Controls_for_Public-Commercial

Solutions for thermostatic mixing valves /

REGULATIONS

HSE guidance recommends the monitoring of Legionella The control of Legionella bacteria in hot
levels where there is a high risk of contamination. and cold water systems
The guidance recognises that the traditional method Guidance on compliance with the relevant parts of
of controlling the risk of Legionella development is the Management of Health and Safety at Work
to produce and distribute higher water temperatures. Regulations 1999 in public premises.
Yet, this significantly increases the risk of scalding (Source: UK Health and Safety Executive, HSG 274
at the point-of-use. Part 2, 2014).
(Source: Centre for Burns, St Joseph and St Luc It recommends: PREMIX SECURITY
Hospital, Lyon, France). - Minimum temperatures to limit the risk
rd
- At 50°C: burns in 7 seconds and 3 degree burns of development of Legionella.
in 100 seconds. - Maximum temperatures to limit the risk of scalding.
- At 60°C: 3 degree burns in 3 seconds on average • At the calorifier outlet the hot water temperature
rd
(5 seconds for an adult, 1 2 seconds for a child). must constantly be above 60°C.
• In storage equipment, water must be maintained
HSG274 Part 2 recommends the installation of
thermostatic mixing valves where there is a high risk at a minimum temperature of 60°C.
of scalding to users e.g. very young, very elderly, • At every point in the distribution system,
infirm, mentally disabled and physically disabled. hot water must be delivered to the outlet at 50°C
- Hot water should be distributed so that it reaches (55°C in healthcare facilities) within one minute
a temperature of 50°C (55°C in healthcare premises) of turning on the tap. PREMIX COMFORT
within one minute at the outlets. The HSE advises that long pipe runs between TMVs
- Thermostatic mixing valves should be installed and outlets should be avoided and should
as close as possible to the point-of-use. not exceed 2 metres in length.
The maximum temperature of sanitary hot water
HSG 274 Part 2, 2014 at the point-of-use is set at: THERMOSTATIC MIXING VALVES
HSE guidance for the control of Legionella bacteria - 44°C for bath fill (46°C if assisted)
in hot and cold water systems states that monitoring - 41°C for showers
for Legionella should be carried out: - 41°C for washbasins,
- when water is treated with biocides or when distribution with special dispensation for catering applications.
temperatures are reduced from HSE guidelines. (Source: Health and Safety Executive information
- where water treatment regime control levels are not sheet 09/12; TMVA Code of Practice, 2000).
being consistently achieved. PREMIX COMPACT
- where there is a high-risk of contamination e.g.
hospitals and care homes. Max 2m of pipework
- where an outbreak of legionellosis has been identified.

A risk assessment is required to identify:
Monitoring frequency of installations for all points-of-
use considered at-risk: ≥ 55°C
• Sentinel points for temperature measurement HW
and bacteriological testing: production
- Once a week in healthcare facilities. >60°C
- Once a month for all other facilities receiving public.
• Bacterial analysis: once a year
DELABIE recommends two water assessments: ≥ 50°C
one on the first draw-off, to detect Pseudomonas
aeruginosa and one on the second to detect
Legionella.
If the hot water systems haven’t been used for several
weeks, samples for Legionella assessment have Pipes between centralised thermostatic mixing valves and the points-of-use should not be longer
to be taken just after the purge of the system than 2 metres.
and within two weeks before receiving the public.
Capacity and length of pipework
Legionella monitoring levels
Pipe length for a capacity of
Material Pipe dimension
Alert level < 100 CFU/L 3 litres 1 litre
15 1 22m 7m
Remedial action level > 100 up to 1,000 CFU/L
Copper 18 1 15m 5m
Curative action level > 1,000 CFU/L 22 1 9m 3m
DN 15 15m 5m
Galvanised steel
CFU/L: Colony Forming Units per litre DN 20 8m 2m
15 2.5 38m 12m
PEX/PER plastic
18 2.5 22m 7m
20 1.9 14m 4m
PR plastic
25 1.9 8m 2m

Thermostatic mixing valves 145