---
title: "Emergency response planning for Legionella incidents"
source_url: https://legionella.io/articles/emergency-response-planning-for-legionella-incidents/
canonical_url: https://legionella.io/articles/emergency-response-planning-for-legionella-incidents/
pillar: "Best Practice & Future of Legionella Control"
summary: "When a sample spikes or a case is reported, who shuts what off first? A UK Legionella emergency plan: the first hour, the investigation and standing down."
primary_keyword: "Legionella emergency plan"
date_published: 2025-09-10
date_reviewed: 2026-06-26
author: "Legionella.io editorial team (REMOTE TECH LTD)"
reviewed_against: "HSE L8 and HSG274 guidance"
region: "United Kingdom"
license: "(c) REMOTE TECH LTD. Quote freely with attribution and a link to source_url."
---

# Emergency response planning for Legionella incidents

Most of your water safety regime runs on a calendar. The emergency plan is the one part that runs on a phone call — the morning a sample comes back high, or the local health protection team rings to say a guest, resident or employee has Legionnaires' disease and your building is on their list. On that morning, the only thing that matters is whether the person holding the phone knows what to switch off, who to call, and what not to touch.

A good Legionella emergency plan answers that in minutes, not meetings. It is short, it names actual people rather than abstract roles, and it lives somewhere the duty manager can reach at 6am on a Sunday — not buried in appendix C of a 90-page risk assessment. It is one chapter of your wider [water safety plan](https://legionella.io/articles/developing-a-comprehensive-water-safety-plan/), but it is the chapter you rehearse.

## What actually counts as an incident

Three situations should trip the plan, and they need different reflexes.

An out-of-range sample result. Your written scheme of control should already define what "out of range" means for each system and what each level triggers; HSG274 sets out the framework for interpreting results and deciding the response [1]. A single high count is a prompt to act and verify, not proof of an outbreak — [Interpreting Legionella test results and counts](https://legionella.io/articles/interpreting-legionella-test-results-and-counts/) covers reading the numbers properly. The figure on the lab report starts the response; it is not the whole of it.

A reported or suspected case. When a clinician diagnoses Legionnaires', it is notified through the health system to UKHSA, and if their investigation points at your premises you may be contacted by the health protection team and asked for records, schematics and access for sampling [2]. You are not running that investigation. You are expected to cooperate quickly and competently, which is far easier when the paperwork is already in order.

A loss of control. A calorifier that has sat at 40C for a week, a cold tank warmed by a failed chiller, a system left charged and idle through a long shutdown. No case, no sample yet — but the exact conditions that produce both.

## The plan, on one page

The reason to write this as a checklist is blunt: nobody reads prose in a crisis. Group it by phase, keep every line a verb, and make each one recordable — a name, a time, a tick. This is the Legionella incident response, stripped to what the first responder actually does.

**Have ready before anything happens**

- Name the people who can declare an incident, and who deputises out of hours.
- Hold a current contact list: responsible person, water treatment contractor, sampling laboratory, the local UKHSA health protection team, and a senior manager with authority to close a facility.
- Pre-agree who can isolate or shut down a system, and who signs off reopening.
- Keep the risk assessment, asset register and schematics reachable remotely, not just on the office wall.

**In the first hour**

- Identify and restrict the implicated outlets or system — stop generating aerosol before anything else.
- Take showers, spray taps and similar fittings out of use with clear signage; fit point-of-use filters where an outlet genuinely must stay available.
- Log the trigger: what was found, where, when, by whom, and the reading or case reference.
- Notify the responsible person and the water treatment contractor.

**Investigate before you sterilise**

- Take samples to characterise the problem before disinfection where practical; sampling supports investigation as well as routine verification, and its placing is set by your risk assessment [3].
- Review recent temperature, flushing and cleaning records for the affected system.
- Walk the system for the likely source: dead legs, low-use outlets, a failed TMV, a cold tank sitting warm.

**Remediate and report**

- Carry out remedial disinfection and cleaning to the method your competent contractor and risk assessment specify; L8 expects the action taken on a control failure to be planned in advance, not improvised on the day [4].
- Check reporting duties: legionellosis can be reportable under RIDDOR where work exposure is the likely cause, and any cooling tower or evaporative condenser carries a separate notification duty to the local authority [5].
- Keep the health protection team updated where a case is involved.

**Stand down and learn**

- Confirm control is re-established against pre-set criteria, including clearance sampling where the scheme requires it.
- Reopen outlets only when the named sign-off is satisfied.
- Hold a short review: what failed, what the records showed, and what changes to the risk assessment or written scheme follow.

## Making the checklist usable, not decorative

A plan only works if the routine parts are maintained while nothing is wrong. Two habits carry most of the weight.

Keep the contact list alive. The most common failure on the day is not a missing procedure — it is a contractor's mobile number that changed eighteen months ago. Refresh the list every time you review the risk assessment, and after any staffing change.

Record the decision, not just the action. "Showers on the third floor isolated at 07:20; point-of-use filters fitted pending resample; reopening requires two clear samples signed off by the responsible person" is worth far more than a tick in a box. Incident records get read later by people who were not there — sometimes a regulator, sometimes the health protection team — and the reasoning is what demonstrates you were in control.

## The bits teams skip

The gaps that hurt are rarely in the obvious steps.

Authority to shut down is the big one. If no one has decided in advance who can take a wing, a spa or a whole building out of service, that decision stalls at the precise moment speed matters. Write the name down now, before you need it.

Out-of-hours coverage is the second. Incidents ignore office hours, and a plan that depends on one person who might be on annual leave is not really a plan.

Then there is the urge to disinfect immediately. It feels decisive, but blitzing a system before sampling can erase the only evidence of where the problem started — and that evidence is exactly what an investigation will ask for.

## A short caveat

This is general guidance, not a stand-in for your competent water treatment specialist or the local health protection team once an incident is live. The action levels that define an excursion, the disinfection method, and the criteria for standing down all depend on your specific systems and risk assessment. A confirmed or suspected case is investigated by UKHSA — your job is to contain, cooperate and document, never to diagnose. Build the plan with the people who will actually have to run it, and test it before the day you rely on it.

## FAQ

### Who declares a Legionella incident — the contractor or us?
You do. The duty holder and responsible person own the decision and the response; a contractor advises and carries out remedial work under that duty. The plan should name, by job title and individual, who can declare an incident and who deputises when they are away.

### Should we shut down the water system the moment we get a high result?
Not reflexively. The first move is to stop aerosol exposure from the implicated outlets and take advice. A full shutdown can introduce its own problems — loss of temperature control, stagnation, a contaminated restart — and rushing to disinfect can destroy sampling evidence. Your written scheme and contractor should guide whether to isolate, treat in place, or shut down.

### Do we have to tell anyone outside the organisation?
Possibly. A diagnosed case is already notified to UKHSA through the health system, and the health protection team may contact you. Separately, the employer may need to report legionellosis under RIDDOR where work exposure is the likely cause, and cooling towers must be notified to the local authority [5]. Confirm the specifics against current HSE guidance for your circumstances.

## Related reading

- [Interpreting Legionella test results and counts](https://legionella.io/articles/interpreting-legionella-test-results-and-counts/)
- [Legionella sampling 101: how and why to test your water](https://legionella.io/articles/legionella-sampling-101-how-and-why-to-test-your-water/)
- [Developing a comprehensive water safety plan](https://legionella.io/articles/developing-a-comprehensive-water-safety-plan/)
- [Data analytics: spotting Legionella risk trends in sensor data](https://legionella.io/articles/data-analytics-spotting-legionella-risk-trends-in-sensor-data/)

## Sources

[1] HSE, "Legionnaires' disease: Technical guidance (HSG274)". https://www.hse.gov.uk/pubns/books/hsg274.htm
[2] UKHSA, "Investigation of Legionnaires' disease: cases, clusters and outbreaks". https://www.gov.uk/government/publications/investigation-of-legionnaires-disease-cases-clusters-and-outbreaks
[3] HSE, "Testing and monitoring your water system for legionella". https://www.hse.gov.uk/legionnaires/testing-monitoring-water-system.htm
[4] HSE, "Legionnaires' disease. The control of legionella bacteria in water systems - Approved Code of Practice and guidance (L8)". https://www.hse.gov.uk/pubns/books/l8.htm
[5] HSE, "Other duties: RIDDOR and notification of cooling towers or evaporative condensers". https://www.hse.gov.uk/legionnaires/what-you-must-do/duties.htm