32 - A number of factors are required to create a risk of acquiring legionellosis, such as:
(a) the presence of legionella bacteria;
(b) conditions suitable for multiplication of the organisms e.g. suitable temperature (20°C–45°C) and a source of nutrients e.g. sludge, scale, rust, algae and other organic matter;
(c) a means of creating and disseminating breathable droplets e.g. the aerosol generated by a cooling tower or shower; and
(d) the presence (and numbers) of people who may be exposed, especially in premises where occupants are particularly vulnerable, e.g. healthcare.
33 - While there will inevitably be common factors associated with the many and varied types of premises being assessed, the individual nature of each site should be taken into account. In complex systems or premises, a site survey of all the water systems should be carried out and should include an asset register of all associated plant, pumps, strainers and other relevant items. This should include an up-to-date drawing/diagram showing the layout of the plant or system, including parts temporarily out of use. A schematic diagram would be sufficient. It should then be decided which parts of the water system, for example, which specific equipment and services, may pose a risk to those at work or other people.
34 - The following list contains some of the factors which should be considered, as appropriate, when carrying out the assessment:
(a) the source of system supply water, for example, whether from a mains supply or not;
(b) possible sources of contamination of the supply water within the premises before it reaches the cold water storage cistern, calorifier, cooling tower or any other system using water that may present a risk of exposure to legionella bacteria;
(c) the normal plant operating characteristics; and
(d) unusual, but reasonably foreseeable operating conditions, for example breakdowns.
35 - Where there is a risk, the significant findings of the assessment should be recorded (if there are five or more employees). In any case, it may be necessary to record sufficient details of the assessment to be able to show that it has been done. The record of the assessment should be linked to other relevant health and safety records and, in particular, to the written scheme referred to in paragraph 53.
36 - Employers are required to consult employees or their representatives on the identified risks of exposure to legionella bacteria and on the measures and actions taken to control the risks. The employees should be given an opportunity to comment on the assessment and control measures and the employer has to take account of these views. It is therefore important for employers to publicise to employees that a legionella risk assessment has been performed and one means by which employers could ensure that employees are informed of the measures and actions taken to control risks, and have an opportunity to comment on the risk assessment, would be by displaying the appropriate parts of the risk assessment.
37 - It is essential that the effectiveness of the control measures is monitored and decisions made on the frequency and manner of this monitoring.
38 - The assessment should be reviewed regularly (at least every two years) and, whenever there is reason to suspect that it is no longer valid. An indication of when to review the assessment and what needs to be reviewed should be recorded. This may result from, for example:
(a) changes to the water system or its use;
(b) changes to the use of the building in which the water system is installed;
(c) the availability of new information about risks or control measures;
(d) the results of checks indicating that control measures are no longer effective;
(e) a case of Legionnaires’ disease/legionellosis is associated with the system.
