What is ACOP L8?

ACOP L8 is the HSE's Approved Code of Practice for controlling legionella in water systems. Its full title is "Legionnaires' disease: The control of legionella bacteria in water systems", the current edition is the fourth (2013), and it tells anyone in control of a water system how to meet their legal duty to assess and control the risk.

It is often shortened to L8 or written ACoP L8, and people sometimes call it "the L8 regulations", though it is a code of practice rather than a regulation. When someone refers to an L8 risk assessment, they mean a legionella risk assessment carried out to meet this code. This page explains what ACOP L8 is, the legal weight it carries, what it actually requires, and how it sits alongside HSG274 and the law.

What ACOP L8 is

L8 is a short, framework document. It does not try to give every technical figure. Instead it sets out the duties that anyone responsible for a water system must discharge, and it points to the detailed technical guidance in HSG274 for the practical methods. "L8" is the HSE's publication number for it, which is why the number appears with no words behind it, in the same way HSG274 is a publication number rather than an acronym.

The document has two components bound together: the Approved Code of Practice text itself, which has the special legal status described below, and accompanying guidance. When people talk about "HSE legionella guidance" or "HSE ACOP L8", they usually mean this combined document.

The special legal status of an Approved Code of Practice

This is the part worth being precise about, because it is widely misunderstood. ACOP L8 is not a statutory instrument, so strictly it is not "the L8 regulations". The legal duty to control legionella comes from the Health and Safety at Work etc. Act 1974 and the Control of Substances Hazardous to Health Regulations (COSHH).

What makes L8 different from plain guidance is its approved status. If a duty holder is prosecuted for a breach of health and safety law, and it is shown they did not follow the relevant provisions of L8, the court will find them at fault unless they can prove they met the duty in some other, equally effective way. That reverse burden is why, in practice, following ACOP L8 is treated as the benchmark for compliance, and why an enforcing officer will measure your arrangements against it.

What ACOP L8 requires you to do

Stripped to its core, L8 requires a repeatable management cycle. The duty holder must:

1. Identify and assess the risk. Carry out a legionella risk assessment of the water system, following the method in the British Standard BS 8580-1.
2. Appoint a responsible person. Name a competent responsible person to take day-to-day charge of managing the risk.
3. Prepare a written scheme of control. Set out the controls, who does them and how often, in a written scheme.
4. Implement, manage and monitor. Carry out the controls, monitor the system (temperatures, flushing, inspections) and act on anything out of range.
5. Keep records and review. Record what is done, and review the assessment regularly and whenever it may no longer be valid.

None of these steps, on their own, makes a system safe. What they do is manage the risk and give you the evidence, which is exactly what the law and an inspector expect to see.

ACOP L8 and HSG274: how they fit together

The two documents are designed to be read together, and confusing them is common. L8 is the framework; HSG274 is the technical manual. When you need to know a temperature, a monitoring frequency or how to control a particular type of system, the answer is in HSG274, which is published in three parts covering evaporative cooling systems, hot and cold water systems, and other risk systems such as spa pools. When you need to know your legal duties and how they will be judged, that is L8.

Put simply: L8 sets the standard you are measured against, and HSG274 describes one recognised way to reach it. You can depart from the technical detail in HSG274 if you achieve the same standard of control another way and can justify it, but the framework duties in L8 are the ones the enforcing authority holds you to.

Who L8 applies to

ACOP L8 applies to any employer, self-employed person or person in control of premises where a work activity involves a water system that could expose people to legionella. In practice that reaches almost every non-domestic building, and it also catches landlords with communal or shared water systems and the owners of holiday lets. The extent of what you need to do is proportionate to the risk: a small, low-risk premises with mains-fed outlets needs far less than a hospital with cooling towers, but the duty to assess and control applies to both.

How to comply with ACOP L8

Compliance is not a certificate or a one-off task. It is the management cycle above, kept up over time and evidenced in records. Start with a risk assessment, put the findings into a written scheme of control, run the monitoring on a schedule, and keep the results in a log book. The full text of the code is published by the HSE, and for the practical figures behind each control, see HSG274 and the temperature control guidance.