Legionella Risk Assessment: The Walk, the Temperatures, the Document

A legionella risk assessment is a written assessment of where legionella bacteria could grow and spread in a building's water systems, who could be exposed, and how the risk is controlled. In the UK it's a legal duty for employers, landlords and anyone in control of premises, and the Health and Safety Executive's Approved Code of Practice L8 and technical guidance HSG274 set out how to do it. It covers the hot and cold water system and anything else that can make a spray, such as cooling towers and spa pools. It ends in a control scheme: what gets checked, how often, and by whom.

That's the paragraph. The rest of this page covers who has to do one, how often, what happens if you don't, and then the walk itself, from the incoming main to the furthest tap, with the temperatures that decide it.

Why water gets its own assessment

Legionella bacteria occur naturally in rivers and lakes. The trouble starts when they get into a building's water and find what they like: water between roughly 20°C and 45°C, standing still, with scale, sludge or biofilm to feed on. Above 60°C they die off quickly. Below 20°C they stay dormant.

People catch Legionnaires' disease, a serious and sometimes fatal pneumonia, by breathing in fine droplets from a shower, a spray tap, a spa pool or a cooling tower. Older people, smokers and anyone with a weakened immune system are most at risk, which is why care homes and hospitals work to tighter figures.

So the assessment comes down to three questions. Where can water sit at the wrong temperature? Where can it stand still? Where can it become a spray someone breathes?

Who has to do one in the UK

The legal basis is the Health and Safety at Work etc. Act 1974, the Management of Health and Safety at Work Regulations 1999 and COSHH. HSG274 comes in three parts: Part 1 for evaporative cooling systems, Part 2 for hot and cold water systems, and Part 3 for other risk systems such as spa pools and humidifiers.

• The duty holder is the employer, or the person in control of the premises. That includes landlords, managing agents and facilities managers. They must make sure the assessment is done and acted on.
• The responsible person is someone the duty holder appoints to run the control scheme day to day. They need to be competent, meaning they know the system, the risks and the controls. No particular certificate is required.
• Landlords of homes have the same duty to assess and control the risk. HSE says most landlords can do this themselves, that a professional isn't required, and that there is no legal requirement for a "legionella certificate". A flat with a combi boiler and no stored water is usually low risk, and the assessment can say so in a page.

If you have five or more employees, the significant findings must be written down. Everyone should write them down anyway. An assessment that exists only in someone's head can't be shown to an inspector, a tenant or an insurer.

How often

There is no fixed legal interval. ACOP L8 says to review the assessment regularly and whenever there's reason to think it's no longer valid. That means when:

• the system changes: a new tank, a refit, outlets added or removed
• the building's use changes: offices become flats, a wing closes, occupancy drops
• more vulnerable people move in
• monitoring shows the controls aren't working
• a case of Legionnaires' disease is linked to the building

Reviewing every two years is common industry practice, and many clients and insurers ask for it. It's a sensible default, not the law. A building refitted last month needs a new assessment now, whatever the date on the old one.

Records. HSE guidance asks for monitoring and inspection records to be kept for at least five years.

What happens if you don't

In the UK, HSE or the local authority enforces legionella control, depending on the premises. They can serve improvement or prohibition notices, and they can prosecute. Nobody has to fall ill first, because failing to assess and control the risk is the offence in itself. Health and safety fines are unlimited, and the sentencing guidelines scale them to the organisation's size and how culpable it was.

The worse consequence is the one the law exists to prevent. When an outbreak is traced to a building, the investigators ask for the assessment, the schematic and the monitoring records. "We had one done years ago and it's in a folder" doesn't go well.

Outside the UK

The method is the same everywhere, even where the legal duty isn't.

• United States. The industry standard is ASHRAE 188, which sets out a water management program for buildings, and the CDC publishes a free toolkit for writing one. CMS expects healthcare facilities to have water management policies, and some jurisdictions, New York among them, regulate cooling towers directly.
• Australia. Each state and territory sets its own rules. In NSW, for example, the Public Health Regulation requires cooling towers to be registered and run under a risk management plan. AS/NZS 3666 is the technical standard.

Check the local rules. The walk is the same.

1. Before you walk: the schematic

You can't assess a system you can't draw. Start with, or build, a schematic showing where water comes in, where it's stored, where it's heated and where it goes. Alongside it, keep an asset register of every tank, calorifier, heater, TMV, shower and outlet.

• Where are the incoming main and the stopcock?
• How many cold water tanks are there, and where?
• How is hot water made: calorifiers, cylinders, combis, point-of-use heaters?
• Is there a return loop, or does water sit in long runs?
• Which outlets are nearest and furthest from each tank and heater? Those are your sentinel outlets.
• Are there any cooling towers, spa pools, humidifiers or water features?

If the drawings are older than the last refit, assume they're wrong.

2. Incoming mains and cold water storage

• Incoming mains temperature. Take a reading at the tap nearest the main. It's the baseline for everything cold.
• Tank condition. Check the lid is fitted and secure, the overflow and vent are screened, and the tank and pipework are insulated. Look inside for debris, insects, rust and sediment.
• Tank water temperature should be below 20°C. A tank in a warm loft or plant room creeps above that in summer.
• Size against use. A tank sized for a full building that now serves half of it holds water for days.
• Access. Nobody checks a tank they can't reach.

Photograph the inside of every tank you open. It's the only record of what it looked like.

3. Hot water plant

• Stored hot water at 60°C or above. Read the calorifier or cylinder thermometer, and check the thermometer works.
• Flow and return. On a recirculating system the return should come back at 50°C or above (55°C in healthcare). A low return means part of the loop is running cool.
• Sediment. Calorifiers collect sludge at the base, where the water is coolest. Check there's a drain valve and a record of it being used.
• Expansion vessels can hold stagnant water. Note whether they're a flow-through type.
• Point-of-use heaters and combis hold little water and turn it over fast, so they're usually lower risk. List them anyway.

4. The outlets, and the temperatures that decide it

This is where assessments are won or lost, because it's where the thermometer goes in the water.

Start with the sentinel outlets. If the furthest tap on the top floor reaches 50°C inside a minute, the loop is probably doing its job. If it takes three minutes, water is sitting at the wrong temperature somewhere along the way, and you've just found where to look.

Note every thermostatic mixing valve (TMV). They're fitted where scalding is the bigger risk, in care homes, schools and accessible bathrooms. But they leave warm water between the valve and the tap, so they belong close to the outlet and on a maintenance schedule.

5. Showers, spray and little-used outlets

• Showers and spray taps make the droplets that carry legionella into lungs, and their heads and hoses collect scale and biofilm. HSE guidance commonly points to cleaning, descaling and disinfecting them quarterly.
• Little-used outlets include the guest-room shower, the cleaner's sink and the staff kitchen in a half-empty office. The usual control is to flush them at least weekly and record it.
• Flexible hoses. Some rubbers support bacterial growth. Note any that look perished or non-standard.

In hotels, schools and seasonal sites, the little-used list is the most important list in the document, and it changes with occupancy.

6. Dead legs and blind ends

A dead leg is pipe that used to feed something and now doesn't, like the branch to a removed sink. A blind end has no outlet at all. Water sits in both indefinitely.

• Look where fixtures have been removed: capped pipes behind panels, under counters, above ceilings
• Ask about refits, because that's when dead legs are made
• Record each one's location and length, and recommend cutting it back to the live pipe

They're among the most common findings and the easiest to fix.

7. Cooling towers, spa pools and other risk systems

• Cooling towers and evaporative condensers are the high-risk end. In the UK they must be notified to the local authority, and HSG274 Part 1 sets out their control regime: water treatment, drift eliminators, microbiological sampling, cleaning. If there's one on site and nobody knew, that's the headline finding.
• Spa pools and hot tubs hold warm water, aerate it and put it under people's faces. They need their own treatment and monitoring regime.
• Other systems include humidifiers, fountains, vehicle washes, hose reels and emergency showers. Anything that stores water at the wrong temperature and makes a spray goes on the list.

The document: what it needs to say

The assessment isn't finished when the walk is. It's finished when the control scheme is written and someone has agreed to run it. It should contain:

1. Premises, date, assessor, duty holder and responsible person
2. System description and schematic
3. Findings, each with a location, a photo and a temperature reading where there is one
4. A risk rating for each part and overall, with the reasoning: who is exposed, how vulnerable they are, how likely the risk is
5. A control scheme of actions, each with an owner and a date
6. A monitoring schedule saying what's checked, how often and where it's recorded
7. A review date, and the changes that would bring it forward

Typical frequencies from HSG274 Part 2 (your assessment sets your own):

What most legionella risk assessments get wrong

Desk-top assessments with no walk. Written from last year's report and a set of drawings, without anyone opening a tank or running a tap. They read well, but they describe a building that may no longer exist.

Temperatures never actually taken. "Hot water satisfactory" with no number next to it. The whole assessment turns on readings. No reading, no finding.

No schematic. Without one, nobody can say which outlets are sentinels or where the dead legs are.

Little-used outlets forgotten. The shower in the closed wing is usually the one that matters.

The control scheme stops at the page. It recommends monthly checks and weekly flushing, but nobody is named to do them and nobody records them. Two years later the review finds the same problems. Without a working monitoring log behind it, the assessment is just a list of intentions.

Doing it on site

A legionella walk means a plant room, a loft, a riser cupboard and forty taps, with a thermometer in one hand, a torch in the other and a stopwatch running. Nobody fills in a form on a phone like that. The readings go on the back of a glove, and by the time they're typed up at a desk, "furthest tap, second floor, 46 after a minute" has become "hot water generally satisfactory".

Speak while you walk, and the document the law or the client wants writes itself. Read the thermometer, then say the number and where you are, and photograph what you're looking at. For example: "Plant room, calorifier one, flow 62, return 53, photo of the gauge. Loft tank, lid on, insulation split at the overflow, photo, water 17 degrees. Sentinel nearest, ground-floor kitchen: hot 56 inside thirty seconds, cold 13 at two minutes. Sentinel furthest, second-floor en-suite: hot only 46 after a minute, that's a fail. Room 12 shower not used since the refit, head's scaled, add it to the weekly flush list." Every reading has a place, a time and a photo, and the finding exists before you've left the building.

Related

• Plumbing inspection report: the water system walk, fixture by fixture
• General workplace inspection: the premises check around it
• EICR for landlords: the other UK landlord safety duty
• Rental property inspection checklist: the room-by-room walk where a landlord spots water problems between assessments
• Hotel room inspection checklist: a classic legionella setting, with a shower in every room and occupancy that comes and goes

Frequently asked questions

What is a legionella risk assessment? A written assessment of where legionella could grow and spread in a building's water systems, who could be exposed, and how the risk is controlled. In the UK it's required under health and safety law, and HSE's ACOP L8 and HSG274 explain how to do it.

Who is responsible for a legionella risk assessment? The duty holder: the employer or person in control of the premises, including landlords and managing agents. They can do it themselves if they're competent, or get someone competent to do it, and they should appoint a responsible person to run the controls.

How often should a legionella risk assessment be done? The UK has no fixed legal interval. Review it regularly, and whenever the system, the building's use, the occupants or the monitoring results change. Every two years is common practice.

Do landlords need a legionella certificate? No. HSE says there's no legal requirement for a legionella certificate or routine testing in ordinary rented homes. Landlords must still assess and control the risk, and most can do that themselves.

What temperatures control legionella? Store hot water at 60°C or above. At outlets it should reach at least 50°C within one minute (55°C in healthcare). Cold water should be below 20°C within two minutes.

What is a sentinel outlet? An outlet nearest to or furthest from a tank or heater. Checking temperatures there each month shows whether the whole system is reaching its targets.