When is an additional legionella risk assessment needed?

An additional legionella risk assessment is needed when the existing assessment can no longer be relied on to represent the actual risk of exposure. This may be because the circumstances have changed, new evidence has emerged, or the assessment did not adequately address a relevant part of the water system, building or management arrangements.

Under the Control of Substances Hazardous to Health Regulations (COSHH), the assessment must be suitable and sufficient and kept under review. The HSE’s ACOP L8 and HSG274 guidance also expect the responsible person to reassess risk when there is reason to believe the existing assessment is no longer valid or when there has been a significant change. An additional assessment is therefore not simply an administrative exercise; it is a way to establish whether existing controls remain appropriate.

Situations that can require a further assessment

• Alterations to the water installation: New pipework, plant, storage vessels, outlets, treatment equipment or changes to circulation can introduce different conditions for bacterial growth or aerosol formation. A review should establish whether the revised system has created dead legs, low-use outlets, temperature-control issues or other risks that the original assessment did not consider.
• Changes to a building or part of a building: Refurbishment, an extension, a change of tenancy or the opening of previously unused areas may affect how water is stored, distributed and used. Areas brought back into service should not automatically be treated as adequately controlled without checking their condition and usage.
• Changes in the people who may be exposed: A change in occupants, residents, employees, visitors or service users may alter the consequences of exposure. Particular consideration is needed where people may be more susceptible to serious illness, including some healthcare, care, residential or supported-living settings.
• Changes in management or responsibility: A new owner, facilities provider, contractor or responsible person may need to confirm who controls each part of the system and whether the written scheme, monitoring arrangements and escalation procedures remain suitable.
• Unsatisfactory monitoring or testing results: Results that indicate inadequate temperature control, ineffective disinfection, contamination or recurring variation should prompt investigation. The appropriate response may include a focused assessment of the affected system, followed by a wider assessment if the cause or extent is uncertain.
• Evidence that control measures are not being followed: Missed monitoring, incomplete records, uncompleted remedial work or repeated failures in flushing and maintenance can indicate that the documented arrangements do not match actual practice. A further assessment can test both the technical controls and the management system supporting them.
• Water quality or operational incidents: An incident involving contamination, a significant interruption to treatment, loss of circulation or another abnormal event should be assessed before the system returns to normal operation. The assessment should consider immediate controls, the underlying cause and whether existing procedures need to change.

An additional assessment is not always a complete replacement. If the change is limited and clearly defined, a competent assessor may be able to produce a supplementary assessment covering the affected equipment, area or activity. Where several aspects have changed, records are unreliable, or the original assessment is outdated or incomplete, a new assessment of the whole relevant system is more appropriate. The decision should be based on the risk, not on the preferred document format.

The assessment should examine the physical water systems as they exist, not only design drawings or previous documents. It should consider sources of water, storage and distribution, temperatures, circulation, outlets, usage patterns, access for maintenance, exposure routes and the effectiveness of existing controls. It should also identify the responsible people, their competence and the arrangements for monitoring, corrective action and verification.

After an additional assessment, the responsible person should:

1. Compare the findings with the current written scheme and control procedures.
2. Deal with any immediate risk, including restricting use of affected outlets or equipment where appropriate.
3. Assign remedial actions to named personnel or contractors and set suitable priorities.
4. Update monitoring, flushing, cleaning, maintenance or treatment arrangements where the assessment requires it.
5. Communicate relevant changes to those who operate, maintain or use the system.
6. Keep the assessment, findings, actions and supporting evidence with the legionella control records.

A further assessment should also be considered where a competent person cannot confirm that the existing document covers the system accurately. Missing asset information, unexplained changes in water temperatures, unidentified outlets or uncertainty about who is responsible for control can all undermine the reliability of an assessment, even where no incident has occurred.

The assessment should be carried out by someone with sufficient competence, knowledge and practical understanding of legionella risks and the type of water system involved. Where specialist testing, engineering changes or remedial work is recommended, those activities should be coordinated with the assessment rather than treated as substitutes for it. UKAS-accredited water testing can provide useful evidence where sampling is appropriate, but test results alone do not replace a suitable and sufficient risk assessment.

In practice, the key test is whether the current assessment still describes the system, the people exposed and the controls being applied. If it does not, an additional assessment is required to identify the changed risk and establish what must happen next.