Control of legionella bacteria in hot and cold water systems

Health and Safety Executive - Safety Notice
Department Name:	Hazardous Installations Directorate (Offshore Division)
Bulletin No:	HID 5-2010-1
Issue Date:	21 May 2010
Target Audience:	Offshore Industry
Key Issues:	This notice is to remind duty holders of the requirement to: identify and assess sources of risk for legionella bacteria in hot and cold water systems, and take steps to prevent or control the risk by putting adequate controls in place and maintain and monitor those controls to ensure effectiveness

Introduction:

This notice is to remind duty holders of the requirement to:

identify and assess sources of risk for legionella bacteria in hot and cold water systems, and
take steps to prevent or control the risk by putting adequate controls in place and maintain and monitor those controls to ensure effectiveness.

This follows recent inspections of offshore installations, which have identified significant failings in the control of legionella bacteria in hot and cold water systems and resulted in formal enforcement action being taken against the duty holders concerned.

Background:

Legionnaires' disease is a potentially fatal form of pneumonia caused by the bacterium legionella pneumophila. The predominant route of infection is inhalation of contaminated aerosols. On average there are approximately 300 - 500 reported cases of Legionnaires' disease each year in the UK. One case has been reported for offshore in the last ten years but not everyone exposed will develop symptoms and those that do not develop the full blown disease may present with mild flu like symptoms. Although the risk of contracting the disease through exposure offshore is low; legionella bacteria are known to colonise and multiply in hot and cold water systems on offshore installations.

Action required:

Duty holders are required to assess the risks from legionella bacteria within their potable water systems and put in place a scheme to prevent or control the risk. In relation to offshore installations the actions required will include, but are not limited to, the following:-

Assessing and managing the risk

Ensure that the legionella risk assessment has been reviewed within the past two years,
Have a written scheme for preventing or controlling the risk,
Carry out all control measures identified by the risk assessment and keep a record of the precautions taken, and
Appoint a competent person to be managerially responsibly for this.

Preventing and controlling risk

For water originating from a storage tank onshore, seek documentary evidence confirming the quality of water provided by the supplier for each delivery (water supplied directly to a supply vessel from a standpipe connected to the public main should already meet quality standards).
Ensure that potable water delivered to the installation contains adequate (0.2 - 0.5 ppm) levels of biocide. This may not always be possible and duty holders may require an alternative control measure. This could be achieved by isolating the cargo water received from the supply vessel in a storage tank on the installation, adding sufficient biocide with a contact time of 30 minutes until the biocide level is at least 0.2 ppm, before allowing the delivered water to enter the potable water system.
Ensure that potable water transfer hoses are capped when not in use, disinfected at regular intervals and replaced, in accordance with manufacturer's guidelines, as part of the planned maintenance scheme.
Ensure that bunkering stations have a facility to allow flushing of potable water transfer hoses and permit acceptance sampling of water from supply vessels. This is also required to allow effective disinfection of hoses to take place.
Ensure that all potable water storage tanks, including header tanks, are inspected on an annual basis and any necessary remedial works carried out.
Ensure that calorifiers are fitted with shunt pumps to prevent thermal stratification within the calorifiers. Temperature gauges should be fitted on the flow and return pipework to ensure that outgoing water is at least 60°C and the return is at least 50°C.
Ensure that measured quantities of biocide are added to the potable water system to provide biocide levels in all parts of the system of between 0.2 ppm and 0.5 ppm at all times.
If fitted, ultra violet filtration units should be positioned on the system before biocide is added as UV radiation is known to reduce biocide levels. It is important to note that UV filtration units are not effective for disinfection as they only work at point of application and research has shown that biofilms carrying legionella bacteria can pass the UV filtration unit. Such systems must always be used in combination with biocide treatment.
Monitor biocide levels in the accommodation units preferably on a daily basis and adjust dosing rates accordingly.
Ensure that monthly checks are carried out on sentinel taps to ensure that the cold water temperature is below 20°C after running for up to two minutes and the hot water temperature is at least 50°C within a minute of running the water.
Potable water should be sampled for bacteriological and chemical analysis at least every three months. Microbiological monitoring for legionella bacteria should be carried out in accordance with Legionnaires' disease. The control of legionella bacteria in water systems. Approved Code of Practice and Guidance¹

Relevant legal documents:

The relevant legal requirements are:

References:

You can find more relevant information in the following publications:

Legionnaires' disease. The control of legionella bacteria in water systems. Approved Code of Practice and guidance L8 Third Edition HSE Books 2000 ISBN 978 0 7176 1772 2
Control of substances hazardous to health. The Control of Substances Hazardous to Health Regulations 2002 (As Amended) Approved Code of Practice and guidance L5 Fifth edition HSE Books 2005 ISBN 978 0 7176 2981 7
UK Offshore Operators Association (now UK Oil and Gas) Guidelines for Environmental Health for Offshore Installations 2007
See also Legionnaires' disease

Further information:

Any queries relating to this notice should be addressed to:

OSD 5.4
Health and Safety Executive
Hazardous Installation Directorate
Offshore Division
Lord Cullen House
Fraser Place
Aberdeen
AB25 3UB

General note:

Please pass this information to a colleague who may have this Product/Equipment or operate this type of system/process.