Two HSE Approved Codes of Practice sit under the Diving at Work Regulations 1997, and they are constantly confused. L103 is offshore. L104 is inland/inshore. Getting that right — and the duties behind it — is the difference between a clean inspection and an enforcement notice.
If you run commercial diving in the UK, two letters and three digits decide which rulebook governs your project: L103 or L104. They are both HSE Approved Codes of Practice (ACoPs), both made under the same parent legislation, and they are routinely mixed up — including in supplier documentation that ought to know better. This piece sets out the precise difference, the duties that flow from each, and the paperwork failures that turn up most often when an HSE diving inspector or a client's auditor comes calling.
Everything below is drawn from the HSE's own published guidance under the Diving at Work Regulations 1997 (SI 1997/2776) and the ACoP family at hse.gov.uk/diving/acop.htm. Where the regulations or HSE guidance are the source, that is noted — operators must still hold their own legally-obtained copies of the ACoPs themselves.
The Diving at Work Regulations 1997 are the overarching law for any diving project where at least one person is at work. They are deliberately goal-setting rather than prescriptive — they tell you what must be achieved, and the Approved Codes of Practice tell you how to achieve it for a particular kind of diving. An ACoP has a special legal status: follow it and you are taken to have complied with the law it covers; depart from it and you must show you achieved compliance some other way.
There are five ACoPs in the diving family, all revised as second editions and in force since 8 December 2014:
For most commercial contractors, the choice is between the first two. The other three apply only if your work is genuinely recreational instruction, media, or scientific/archaeological in nature — and each carries its own duties regardless of depth.
This is the part that gets muddled, so let's be exact. The split is by where and how you dive, not by who you work for.
Applies to diving at sea outside UK territorial waters (broadly beyond the 12 nautical mile limit), continental-shelf activities, and diving connected with offshore oil and gas pipelines and structures even within the 12-mile limit. Critically, L103 also governs closed-bell and saturation diving wherever it takes place, dynamically-positioned (DP) vessel-based diving, and any dive exceeding 50 metres — those higher-hazard modes follow L103 even if the water is technically inshore.
Applies to inshore waters within UK territorial limits (broadly within 12 nautical miles) and to inland sites: docks, harbours, rivers, culverts, canals, lakes, ponds, reservoirs, tanks and even swimming pools. It covers the bread-and-butter of UK commercial diving — civil-engineering works, marine and harbour projects, and fish farming. It excludes commercial shellfish diving, which the HSE handles separately.
So the working rule for most contractors is simple: if your project is a harbour, river, reservoir, dock or civil-engineering job inside territorial waters, you are in L104 territory. You only step into L103 if you go offshore proper, use saturation or closed-bell systems, dive from a DP vessel, or go beyond 50 metres. Many contractors cite "L103/L104" together as shorthand because they may operate across both worlds, but for any given dive, one of them is the directly applicable code — and the higher-hazard L103 thresholds (saturation, closed bell, DP, 50 m) are the trip-wires worth memorising.
Both ACoPs share the same cast of duty-holders, defined in the regulations. Knowing who is legally responsible for what is the backbone of any diving audit, because inspectors test the chain of responsibility, not just the existence of documents.
| Duty-holder | Core legal duties |
|---|---|
| Diving contractor | The person who plans and conducts the project — appointed in writing before work starts. Owns the diving project plan, the risk assessment it is based on, the appointment of competent supervisors, sufficient suitable plant, the diving operation records, and notifying the HSE of their particulars. Also the responsible person for RIDDOR reporting. |
| Diving supervisor | Appointed in writing by the contractor for each diving operation. Directs the operation in line with the plan and the law, confirms on the day that divers are competent, equipment is appropriate and the risk assessment still fits the conditions, and maintains adequate communication with divers in the water. |
| Diver | Holds a valid approved qualification for the activity, a current certificate of medical fitness to dive, keeps a personal diving log, and does not dive if aware of any condition making them unfit. Must be competent for anything they may reasonably be expected to do. |
| Client & others | Under Regulation 4, every participant — including the client, site owner, vessel and crane operators — must take the measures reasonable for someone in their position to ensure the regulations are complied with. The client cannot simply delegate the risk away. |
Each duty crystallises into a record an auditor will ask to see. The essential set is the same under L103 and L104:
After years on the other side of audits, the failures cluster in the same places. None of them are exotic — they are almost always a record that lapsed, drifted generic, or could not be produced on the day.
Notice the pattern: the regime is rarely the problem. The paperwork is. The contractors who sail through inspections are not the ones with the thickest folders — they are the ones who can put their hand on the right current record in seconds, because their system keeps it live.
This is the half worth automating. PICMS's Commercial Diving pack keeps the project records — RAMS and dive plans, competence files, medical certificates, plant and certification registers, and dive logs — in one place with expiry tracking on the things that lapse: medicals, cylinder inspections, air-quality tests and qualifications. It is built to keep that documentation audit-ready and aligned with the relevant ACoP and IMCA D018/D023/D040 reference areas, so that when an inspector or client auditor arrives, the current record is already to hand rather than buried in a van.
To be plain about what software can and cannot do: PICMS does not make anyone "compliant" or "IMCA-compliant," and it does not replace the supervisor's judgement on the day or a competent person's ownership of the diving project. What it does is make sure the evidence behind your L103 or L104 obligations is complete, current and traceable — which, on inspection day, is most of the battle.
The PICMS Commercial Diving pack keeps RAMS, dive plans, competence files, medicals, plant certs and dive logs in one place — with expiry tracking and alignment to the relevant ACoP and IMCA reference areas.