What is the difference between ACOP L8 and HSG274?
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Key points
- ACOP L8 sets the duty; HSG274 explains how to meet it. L8 tells you what you must achieve, HSG274 gives the temperatures, frequencies, and procedures.
- L8 has special legal status: if you did not follow it, a court can use that as evidence of a breach unless you prove you complied another way.
- HSG274 is guidance, with no special legal status, but it is the HSE's own benchmark, so following it is the usual route to demonstrating compliance.
- Most hot and cold water systems need HSG274 Part 2; Part 1 covers cooling towers and Part 3 covers spa pools and other specialist systems.
- You do not choose between them. You use both: L8 frames the duty, HSG274 supplies the working detail.
ACOP L8 is the Approved Code of Practice that sets out your legal duty to control legionella, and HSG274 is the HSE technical guidance that shows you how to carry that duty out. They are not alternatives. L8 is the short document that defines what must be done; HSG274 is the much longer document that translates it into target temperatures, monitoring frequencies, and procedures for each type of water system.
People search for the difference because the two documents are always mentioned together, usually as "ACOP L8 and HSG274". The pairing is the point. Neither works alone: L8 without HSG274 leaves you knowing you must control the risk but not how, and HSG274 without L8 is practical advice with no framework holding it together. The pages on ACOP L8 and HSG274 go into each document separately; this page is about how they fit together.
The difference at a glance
| ACOP L8 | HSG274 | |
|---|---|---|
| What it is | Approved Code of Practice: Legionnaires' disease, the control of legionella bacteria in water systems | HSE technical guidance: Legionnaires' disease, technical guidance, in three parts |
| Legal status | Special status under the Health and Safety at Work Act: failure to follow it can be cited in court as evidence of a breach | Guidance only: no special legal status, but the recognised industry benchmark |
| What it contains | The duties: risk assessment, written scheme of control, competent persons, record keeping | The methods: temperatures, flushing regimes, monitoring frequencies, disinfection procedures, sampling guidance |
| Who it speaks to | Duty holders and responsible persons deciding what must be in place | The people carrying out and supervising the day-to-day controls |
| Size and style | Short, duty-by-duty, each paragraph carrying legal weight | Long, practical, organised by system type |
What the special legal status of L8 actually means
An Approved Code of Practice sits between the law and ordinary guidance. The Health and Safety at Work Act and COSHH create the duty to control the risk from legionella, but they do not say how. ACOP L8 fills that gap, and Parliament has given it a particular weight: if you are prosecuted for breaching the underlying duty and the court is satisfied that L8 was relevant, your failure to follow the code is treated as evidence of the breach. The only defence is to show you achieved compliance by equally effective means.
That is a deliberately one-way arrangement. Following L8 is a safe harbour; departing from it shifts the burden of proof onto you. The full framework is explained on our legionella regulations page, but the practical takeaway is simple: treat L8 as the rulebook, because a court will.
Where HSG274 fits
HSG274 has no special legal status, and the HSE says so itself. But it is the HSE's own detailed description of what good control looks like, written by the same regulator that would inspect or prosecute you. If your controls follow HSG274 Part 2, you will in almost every case also be satisfying L8. If you decide to do something different, for example a different monitoring frequency or a novel treatment method, HSG274 becomes the yardstick your alternative will be judged against.
So the honest summary is: HSG274 is optional in law and close to mandatory in practice. Its three parts matter because they are scoped to different systems. Part 1 covers evaporative cooling systems, Part 2 covers hot and cold water systems, and Part 3 covers other risk systems such as spa pools. A landlord with a single flat needs Part 2; a site with a cooling tower needs Part 1 as well, and a holiday let with a hot tub should also look at HSG282, the spa-pool guidance that works alongside HSG274.
L8 is the exam question; HSG274 is the worked answer. A court asks whether you met the duty in L8, and HSG274 is the standard your answer will be measured against.
How the two documents work together on one system
Take an ordinary office with stored hot and cold water. L8 requires a suitable and sufficient risk assessment, a written scheme of control, a competent responsible person, and records. HSG274 Part 2 then supplies the substance: hot water stored at 60°C and delivered at outlets at at least 50°C within one minute, cold water below 20°C within two minutes, weekly flushing of little-used outlets, periodic tank and calorifier inspections, and records kept for at least five years. The assessment identifies what applies to your system; the written scheme schedules it; the records evidence it.
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.
You can see the temperature figures in context on the legionella temperature chart, and check your own readings against them with the temperature checker. If you are starting from scratch, the risk assessment builder walks through the duties L8 sets, structured the way HSG274 expects the controls to be recorded.
A common misunderstanding
Neither document is a certificate and neither certifies anything. A risk assessment, a written scheme, or a set of monitoring records that follow L8 and HSG274 does not prove a system is safe; it evidences that the risk has been assessed and that a control regime is in place and being carried out. That distinction matters when you read supplier claims or buy reports: documents record and structure the work, they do not sign off a building. The duty is continuing, which is why the guidance is built around routine monitoring and review rather than a one-off pass.
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
Is ACOP L8 a legal requirement?
ACOP L8 is an Approved Code of Practice, not a law in itself, but it carries a special legal status. If you are prosecuted for breaching the Health and Safety at Work Act or COSHH and it is shown that you did not follow L8, a court will treat that as evidence against you unless you can show you complied with the duty by equally effective means. In practice, following L8 is the recognised way of meeting the legal duty to control legionella risk.
Do I have to follow HSG274?
HSG274 is technical guidance, so it does not have the special legal status of an Approved Code of Practice. However, it is the HSE's own benchmark for what good control looks like, and following it is normally the most straightforward way to show you have met the duty in ACOP L8. If you choose a different method, you carry the burden of demonstrating that your approach controls the risk to an equivalent standard.
Which should I read first, L8 or HSG274?
Read L8 to understand your duties: assess the risk, prepare a written scheme of control, appoint a competent person, and keep records. Then use HSG274 for the practical detail of how to do it, such as target temperatures, monitoring frequencies, and flushing regimes. L8 tells you what you must achieve; HSG274 tells you how to achieve it in a real water system.
What are the three parts of HSG274?
HSG274 is published in three parts. Part 1 covers evaporative cooling systems such as cooling towers. Part 2 covers hot and cold water systems, which is the part most landlords, employers, and building managers use. Part 3 covers other risk systems, including spa pools, humidifiers, and vehicle washers. Most premises need only Part 2, plus Part 1 or Part 3 if they have the equipment those parts cover.
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