What is HSG274?
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Key points
- HSG274 is the HSE's technical guidance on legionella, full title "Legionnaires' disease: Technical guidance". It sits alongside the Approved Code of Practice ACOP L8 and gives the practical detail behind it.
- It is published in three parts: Part 1 on evaporative cooling systems, Part 2 on hot and cold water systems, and Part 3 on other risk systems such as spa pools and humidifiers.
- L8 sets the legal duties; HSG274 gives the figures and methods. You read them together, and you use only the part that matches the systems you have.
- It contains the core control detail: the 60/50/20 temperature regime, sentinel-outlet checks, the monitoring schedule, and the sampling and action levels.
- HSG274 is guidance, not law, but it is the recognised way to meet the duty. Its findings feed straight into your risk assessment and written scheme.
HSG274 is the Health and Safety Executive's technical guidance on controlling legionella in water systems. Its full title is "Legionnaires' disease: Technical guidance", and it is the document duty holders reach for when they need to know a temperature, a monitoring frequency or how to control a particular type of system.
It works hand in hand with the Approved Code of Practice, ACOP L8. Where L8 sets out the legal duties, HSG274 fills in the practical how. This page explains what HSG274 is, the three parts it is split into and what each covers, how it relates to L8, the key figures it contains, and its legal standing.
What HSG274 is
HSG274 is a technical manual. Unlike L8, which is short and framework-level, HSG274 goes into the detail: the exact temperatures, the intervals for each check, how to take and interpret water samples, and the control measures for every common type of water system. "HSG" is the HSE's series code for guidance documents, so 274 is simply a publication number rather than an acronym that stands for anything.
It replaced the older, single-volume technical guidance and was reissued in three separate parts so that each type of system gets its own dedicated treatment. The three parts were published in 2013 and 2014. The point of splitting it is practical: a landlord with a mains-fed house needs Part 2, while a factory with a cooling tower needs Part 1 as well.
The three parts of HSG274
Each part covers a different family of systems. You use the part or parts that match what you actually have on site, rather than reading all three.
| Part | Systems covered | Typical examples |
|---|---|---|
| Part 1 | The control of legionella in evaporative cooling systems | Cooling towers and evaporative condensers |
| Part 2 | The control of legionella in hot and cold water systems | Calorifiers, storage tanks, taps and showers in almost any building |
| Part 3 | The control of legionella in other risk systems | Spa pools, humidifiers, emergency showers, vehicle washes and misting systems |
Part 2 is the one most duty holders use, because nearly every building has hot and cold water. Part 1 matters wherever there is a cooling tower or evaporative condenser, which also carry a separate legal duty to notify the local authority. Part 3 picks up the specialist systems, and for spa pools it is read with the dedicated guidance in HSG282.
HSG274 and ACOP L8: how they fit together
The two documents are designed to be used side by side, and mixing them up is a common source of confusion. L8 is the legal framework. It tells you that you must assess the risk, appoint a competent person, prepare a written scheme of control and keep records, and it carries the special status of an Approved Code of Practice, which means departing from it puts the burden on you to prove you controlled the risk equally well.
HSG274 has no such special status. It is the technical companion that shows one recognised way to meet those duties. When you need to know the storage temperature for a calorifier, the frequency of a tank inspection or the action level for a water sample, the answer is in HSG274. When you need to know your legal obligations and how an inspector will judge them, that is L8. In short, L8 sets the standard you are measured against, and HSG274 describes how to reach it.
The key figures HSG274 contains
Most of what people look up in HSG274 lives in Part 2, and it comes down to a handful of controls.
- The temperature regime. Store hot water at 60°C and deliver it at 50°C (55°C in healthcare) within one minute at the outlet. Keep cold water below 20°C, reaching that within two minutes. This keeps water out of the 20°C to 45°C band where legionella multiplies.
- Sentinel outlets. The nearest and furthest outlets on each hot and cold loop are designated sentinels and checked monthly, because they represent the temperature extremes of the system.
- The monitoring schedule. HSG274 sets frequencies for each task: monthly sentinel temperatures, quarterly calorifier draining, annual cold water storage tank inspections, quarterly thermostatic mixing valve servicing and regular showerhead descaling and disinfection, all captured in the monitoring schedule.
- Sampling and action levels. Where the risk assessment calls for it, HSG274 explains how to take samples and what the results mean, with defined action levels that trigger review or remedial action.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
Follows ACoP L8 and HSG274 Part 2. Free. No spam.
Is HSG274 a legal requirement?
No. HSG274 is guidance, and following it to the letter is not itself a legal obligation. The duty to control legionella comes from the Health and Safety at Work etc. Act 1974 and the COSHH Regulations, and the code you are measured against is ACOP L8. Because HSG274 lacks L8's approved status, you are free to control the risk by another method, provided it is at least as effective and you can justify the choice.
In practice, though, HSG274 is the path of least resistance. It represents the HSE's own view of good control, so an enforcing officer will expect your arrangements to line up with it or to see a clear, defensible reason why they do not. For the vast majority of duty holders, following the relevant part of HSG274 is the simplest way to demonstrate compliance.
Which part of HSG274 you need
Start from the systems you have. If your building runs on hot and cold water with no cooling tower or spa, Part 2 covers you. Add Part 1 if there is an evaporative cooling system, and Part 3 if you operate spa pools, humidifiers, emergency showers or similar specialist equipment. Whatever the mix, the way you put HSG274 to work is the same: use it to inform a legionella risk assessment, then build the temperatures and check intervals it sets out into your written scheme of control and record them as you go.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
Follows ACoP L8 and HSG274 Part 2. Free. No spam.
Frequently asked questions
What is HSG274?
HSG274 is the Health and Safety Executive's technical guidance on legionella, with the full title "Legionnaires' disease: Technical guidance". It accompanies the Approved Code of Practice ACOP L8 and gives the practical detail behind it: the water temperatures, monitoring frequencies, sampling and control methods a duty holder uses to keep a water system safe. HSG is simply the HSE's series for guidance documents, so 274 is a publication number rather than an acronym.
What are the three parts of HSG274?
HSG274 is published in three parts, each covering a different type of system. Part 1 covers the control of legionella in evaporative cooling systems, meaning cooling towers and evaporative condensers. Part 2 covers hot and cold water systems, which is the part that applies to most buildings. Part 3 covers other risk systems, such as spa pools, humidifiers, emergency showers, vehicle washes and misting systems. You use the part or parts that match the systems you actually have.
What is the difference between L8 and HSG274?
ACOP L8 sets the legal framework and the duties: assess the risk, appoint a competent person, prepare a written scheme of control, keep records. HSG274 is the technical guidance that tells you how to carry those duties out in practice, with the temperatures, monitoring intervals and control measures for each type of system. L8 tells you what you must achieve and carries special legal weight; HSG274 describes one recognised way to achieve it. They are written to be read together.
Is HSG274 a legal requirement?
No, HSG274 is guidance, not law. The legal duty to control legionella comes from the Health and Safety at Work etc. Act 1974 and the COSHH Regulations, and the benchmark for compliance is ACOP L8. HSG274 does not carry the special legal status that L8 does, so you can control the risk by a different method if it is equally effective and you can justify it. In practice, following HSG274 is the straightforward way to show an inspector you have met the duty.
What temperatures does HSG274 require?
HSG274 Part 2 sets out the temperature regime for hot and cold water. Hot water should be stored at 60°C and reach at least 50°C (55°C in healthcare premises) at the tap within one minute of running it. Cold water should stay below 20°C and reach that within two minutes. The reason is that legionella multiplies roughly between 20°C and 45°C, is dormant below 20°C and is killed at 60°C, so keeping water out of that band is the core control.
What is HSG274 Part 2?
HSG274 Part 2 is the part covering the control of legionella in hot and cold water systems. It is the most widely used part because almost every building has these systems. It sets the 60/50/20 temperature regime, explains sentinel-outlet monitoring, gives the monitoring schedule for temperature checks, tank inspections, showerhead cleaning and thermostatic mixing valve servicing, and covers sampling and action levels. If you manage an office, a care home, a hotel or rented housing, Part 2 is the part you will use most.
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