Seveso Directive explained for UK and Norwegian operators

Seveso III is the EU directive for preventing major accidents involving dangerous substances and limiting harm to people and the environment. It covers establishments whose substance inventories meet lower-tier or upper-tier thresholds, including through aggregation. Directive 2012/18/EU sets the EU framework.

For operators, the domestic rules determine what to do. Great Britain uses COMAH 2015, Northern Ireland has separate COMAH legislation, and Norway uses storulykkeforskriften. Don't treat those instruments as interchangeable.

Seveso III replaced Seveso II

The current EU framework is Seveso III, Directive 2012/18/EU. It replaced Seveso II, Directive 96/82/EC, from 1 June 2015. Searches for "Seveso II Directive" or "96/82/EC" therefore lead to the predecessor, rather than the current framework. The replacement date appears in Article 32.

The Directive is in force. For a British site assessment, however, use the operative COMAH provisions rather than treating the Directive as the domestic operating rule.

How lower-tier and upper-tier establishments qualify

A hazardous substance on site doesn't automatically make the establishment a Seveso site. Qualification depends on substance identity, hazard classification and quantity. The assessment covers the whole location under one operator's control, including common or related infrastructure. It isn't limited to chemical manufacturers. These scope rules appear in Articles 2–3.

Use the maximum quantity present or likely to be present at any one time, not annual throughput. The EU definition also includes dangerous substances reasonably foreseeable from a loss of process control. An assessment based only on normal stored stock can therefore miss relevant quantities. See Article 3 and Annex I.

Annex I has two parts. Part 1 gives thresholds for hazard categories. Part 2 lists named substances. Where both cover a substance, the named entry takes precedence. Lower-tier status means reaching column 2 without qualifying for upper tier. Upper-tier status means reaching column 3. Equality counts: the rule is "at or above", not "more than". Annex I supplies the thresholds and notes.

Aggregation can bring a site into scope

Checking each substance against its own threshold isn't enough. The summation rule can qualify an establishment even when no individual substance reaches its standalone threshold. Apply the rule separately to the relevant health, physical and environmental hazard groups, including relevant named substances. Annex I, note 4 sets out the calculation.

For each applicable group, add each quantity divided by its relevant threshold:

• Lower-tier test: sum(qi / QLi) >= 1.
• Upper-tier test: sum(qi / QUi) >= 1.

Here, qi is the substance quantity. QLi and QUi are its lower-tier and upper-tier thresholds. Multiple classifications and the Annex notes affect which quantities belong in each test. The small-quantity exclusion at no more than 2% also has a location condition: the substance cannot initiate a major accident elsewhere on site. It isn't a blanket small-container exemption. See the Annex I notes.

Article 2 excludes specified activities, but some gas storage, processing and tailings activities remain covered. Don't assume that every mining-related establishment is exempt. Check the precise scope provisions.

What the tiers require under the EU framework

Both tiers must notify the competent authority under Article 7. They also need a written, implemented major-accident prevention policy, usually called a MAPP. Article 8 requires policy review at least every five years. Lower-tier management arrangements can use proportionate alternatives that respect Annex III principles. Articles 7–8 set these duties.

Upper-tier establishments also need an Article 10 safety report. It must demonstrate prevention and mitigation measures and the management arrangements. Review is required at least every five years, after a major accident and on other specified triggers. Under Article 12, upper-tier operators prepare internal emergency plans and supply information for external plans. Plans must be reviewed, tested and, where necessary, updated at intervals no longer than three years. See Articles 10 and 12.

Both tiers must cooperate where authorities identify domino-effect groups. Significant modifications or tier changes require advance review and necessary updates under Articles 9 and 11.

This EU-level comparison doesn't settle every national emergency-planning duty. Norway, for example, requires internal plans at both tiers.

Great Britain applies COMAH 2015

The Control of Major Accident Hazards Regulations 2015 apply in Great Britain and commenced on 1 June 2015. Use regulation 2 and Schedule 1 for qualification. They use the same at-or-above column tests, the maximum inventory and separate hazard-group summation. Schedule 1 is the operative GB threshold source. Don't assess a British site from the EU Annex alone.

Both tiers must notify under regulation 6. A new establishment has to notify a reasonable period before construction or operation, and relevant changes need advance notification. Both tiers also need a written MAPP, implemented through a safety management system. Review it on specified changes and at intervals no longer than five years under regulation 7.

Upper-tier operators need a safety report. Regulation 8 sets what it must demonstrate. Regulation 10 requires review at least every five years and on other specified triggers.

For a new establishment, the safety report must be submitted a reasonable period before construction, before operation, or before a modification that changes the relevant inventory, and that step is blocked until the examination conclusions are received. The two-year route is only for a separately defined "other establishment". It isn't a grace period for every new upper-tier site. Check regulation 9 before setting the project timetable.

Upper-tier operators must prepare an internal emergency plan under regulation 12. They must also supply the information the local authority needs for the external plan under regulation 13. The operator reviews, revises where necessary and tests the internal plan at suitable intervals not exceeding three years. The local authority does that for the external plan under regulation 14. New-site duties can arise before operation or relevant modifications.

HSE isn't the sole competent authority. It acts jointly with the relevant environmental regulator. ONR takes HSE's role for nuclear establishments. The environmental partners are the Environment Agency in England, Natural Resources Wales in Wales and SEPA in Scotland. HSE's COMAH introduction explains the joint arrangements.

Northern Ireland has separate rules

Northern Ireland uses the Control of Major Accident Hazards Regulations (Northern Ireland) 2015, not the GB instrument. Its joint competent authority is HSENI and the Northern Ireland Environment Agency, according to HSENI's COMAH guidance. Use that legislation and those regulators for a Northern Irish establishment.

Norway applies storulykkeforskriften

Norway implements Seveso III through the EEA framework using storulykkeforskriften, effective from 1 July 2016. Its tier names are:

• Meldepliktig storulykkevirksomhet: lower tier, reaching column 2 without upper-tier qualification.
• Sikkerhetsrapportpliktig storulykkevirksomhet: upper tier, reaching column 3.

Section 3 also applies aggregation where relevant. Use Norway's own Annex I for calculations, including its conversion provisions, rather than importing an EU threshold worksheet unchanged. The Norwegian regulation contains both the definitions and Annex.

"Meldepliktig" doesn't mean notification is the only duty. Both tiers have systematic prevention and management duties under §4. Section 6 requires notification to DSB, with updates at least every five years. Section 7 requires a documented, implemented prevention strategy, reviewed and updated at least every five years. Upper-tier sites also need a §9 safety report. It must be submitted sufficiently before relevant chemicals are introduced or changed. It must be reviewed and updated at least every five years, and on specified new-knowledge, accident and near-miss triggers. Those duties are in §§4-9.

Section 11 requires both tiers to maintain internal emergency plans and supply external-planning information. Plans must be exercised or tested and reviewed annually, with every element tested within three years. Plans must be updated at least every three years. A new establishment must meet those planning and information duties a reasonable time before operation or a relevant chemical change, and no later than one month before that point. These are Norwegian §11 requirements, not a copy of the EU upper-tier-only rule.

Both tiers must also keep public information current, including electronically. Upper tier has extra proactive information duties. DSB coordinates oversight, but several authorities have roles. Sections 5 and 12 cover these arrangements.

Start with the national inventory test

Before assigning a tier, match the maximum site inventory to the current national schedule. Check named entries, classifications and aggregation before deciding which duties apply. Use GB Schedule 1 or Norway's Annex I for the relevant site.

RegAffairs AI's answer on Seveso coverage and tiers provides a starting point for reading the sources.