What are they?

Major accidents are events that may occur at establishments where certain quantities of hazardous substances are manufactured, used or stored and which may have serious consequences for people's health, property or the environment.

They may include, among other situations, significant releases or spills, fires or explosions resulting from uncontrolled processes. Their effects may remain within the establishment or extend beyond it and affect workers, the general population, the environment and other nearby facilities.

European legislation on the prevention and control of such accidents is known as the Seveso legislation. The current framework is Directive 2012/18/EU (Seveso III), transposed into Spanish legislation through Royal Decree 840/2015 of 21 September, on measures to control the risks inherent in major accidents involving hazardous substances.

For the purposes of Royal Decree 840/2015, a major accident is any event, such as a major release or spill, fire or explosion, resulting from an uncontrolled process at an establishment covered by its scope, which poses a serious, immediate or delayed risk to human health, property or the environment and involves one or more hazardous substances.

The legislation establishes different obligations depending on the quantities and characteristics of the hazardous substances present at the establishment. A distinction is made between lower-tier and upper-tier establishments, with more demanding prevention, safety management, information and emergency planning requirements for upper-tier establishments.

Prevention measures must be based on hazard identification and assessment, the adoption of technical and organisational measures, the maintenance of facilities and equipment, management of modifications, emergency preparedness and continuous improvement of safety.

Royal Decree 840/2015 requires establishments covered by the legislation to have a major-accident prevention policy and a safety management system. Upper-tier establishments must also prepare a safety report.

The prevention of major accidents is not solely the responsibility of the company. The legislation recognises the importance of workers' information, consultation and participation. Internal emergency plans or self-protection plans must be prepared following consultation with the personnel of the establishment and with workers of subcontracted companies or long-term contractors, in accordance with the Occupational Risk Prevention Act.

Prevention must also take into account the so-called domino effect, that is, the possibility that an accident at one establishment may increase the risk of accidents at nearby facilities or that an accident may be aggravated by the presence of other establishments.

What should you do?

If you are a worker

1. Check whether the establishment where you work falls within the scope of Royal Decree 840/2015 and whether it is classified as a lower-tier or upper-tier establishment.
2. Find out which hazardous substances are present, their main hazards and the possible major-accident scenarios that could affect your workplace.
3. Request information about prevention and protection measures, alarm systems, evacuation routes, assembly points and shelter-in-place or other measures planned in the event of an emergency.
4. Take part in the training and drills organised by the company and report any deficiency that could increase the risk of an accident.
5. Check that emergency instructions are also known by workers of contractor and subcontractor companies carrying out activities at the establishment.
6. Participate, directly or through workers' representatives, in matters relating to the prevention of major accidents and emergency measures.
7. Request that modifications to processes, facilities or substances that could increase the risk be subject to an appropriate preventive assessment.
8. If situations involving serious and imminent risk are detected, the measures established under occupational risk prevention legislation and the establishment's emergency procedures must be applied.

The Occupational Risk Prevention Act (Law 31/1995) recognises workers' right to receive information about risks, prevention measures and emergency measures, as well as to be consulted and participate in matters affecting their health and safety.

If you are a workers' representative

Pay particular attention to ensuring that:

1. The risk of major accidents is incorporated into the risk assessment and preventive planning.
2. Workers receive sufficient and understandable information about risks and emergency measures.
3. Personnel have been consulted during the preparation and review of internal emergency or self-protection plans.
4. Workers of contractor and subcontractor companies are taken into account.
5. Appropriate training and drills are carried out and their results are used to improve preventive measures.
6. Changes to facilities, processes or quantities of hazardous substances are assessed before they are put into operation when they may affect the risk of a major accident.
7. Measures are adopted to reduce risks at source, including the substitution of hazardous substances and the application of technical and organisational measures whenever possible.

The coordination of business activities is particularly important at these establishments. When several companies operate at the same workplace, they must exchange information on risks and establish the necessary coordination arrangements to prevent concurrent activities from creating or aggravating risks.

In the event of a major accident

The company must immediately notify the competent authority of incidents or accidents liable to cause a major accident and provide the available information on the circumstances of the accident, the substances involved, their potential effects and the emergency measures taken or planned.

Following an accident, its causes and consequences must be investigated and the necessary measures adopted to limit its effects and prevent a similar accident from occurring again.

For workers, it is essential to follow the instructions established in the establishment's emergency plan and the instructions given by emergency services. Workers should not leave their workplace, evacuate, shelter in place or use protective equipment on their own initiative: previously established procedures and the information provided by the company and the authorities must be followed.

Classification

Annex I of Royal Decree 840/2015 establishes the hazardous substances and hazard categories that determine whether the legislation applies.

The Annex is structured in two parts:

1. Part 1: categories of hazardous substances according to their hazard classification under the CLP Regulation, including health hazards, physical hazards, environmental hazards and other hazards.
2. Part 2: specifically named hazardous substances, together with their corresponding threshold quantities.

Threshold quantities are established for lower-tier and upper-tier establishments. To determine whether an establishment falls within the scope of the legislation, the aggregation rules set out in Annex I must also be applied where appropriate.

The classification of substances and mixtures is carried out in accordance with Regulation (EC) No 1272/2008 (CLP) and its amendments.

Legislation

1. Directive 2012/18/EU of the European Parliament and of the Council of 4 July 2012 (Seveso III) on the control of major-accident hazards involving dangerous substances.
2. Royal Decree 840/2015 of 21 September, approving measures to control the risks inherent in major accidents involving hazardous substances. This is the main Spanish legislation currently applicable to establishments covered by the Seveso legislation.
3. Law 17/2015 of 9 July on the National Civil Protection System, which establishes the general framework for the civil protection system.
4. Royal Decree 524/2023 of 20 June, approving the Basic Civil Protection Standard. Since 2023, this has replaced the previous Basic Civil Protection Standard and formally repealed various previous guidelines and plans.
5. Royal Decree 1196/2003 of 19 September, approving the Basic Civil Protection Guideline for the control and planning of the risk of major accidents involving hazardous substances. This legislation was repealed by Royal Decree 524/2023, but continues to apply on a transitional basis until the new planning instrument replacing it is approved.
6. Royal Decree 1070/2012 of 13 July, approving the State Civil Protection Plan against chemical risk. This was also repealed by Royal Decree 524/2023, but continues to apply on a transitional basis until the planning instrument replacing it is approved.
7. Law 31/1995 of 8 November on Occupational Risk Prevention, particularly its provisions on information, consultation, participation, training, emergency measures and serious and imminent risk.
8. Royal Decree 171/2004 of 30 January, on the coordination of business activities.
9. Regulation (EC) No 1272/2008 (CLP) on the classification, labelling and packaging of substances and mixtures.

References

1. European Commission. Industrial accidents – Seveso III. Official information on the prevention and reduction of industrial accident risks.
2. European Commission – Joint Research Centre (JRC). Major Accident Reporting System (eMARS). European database of major accidents and near-misses involving hazardous substances, intended to facilitate the exchange of experience and lessons learned to prevent new accidents.
3. European Commission – Joint Research Centre (JRC). Internal Emergency Planning. Technical support document for assessing internal emergency planning at Seveso III establishments.
4. European Commission – Joint Research Centre (JRC). Maintenance of Primary Containment Systems. Technical support document on preventing losses of containment of hazardous substances.
5. Directorate-General for Civil Protection and Emergencies. Chemical risk. Official information on the risks associated with establishments where large quantities of hazardous substances are manufactured, stored or handled, and on self-protection measures.
6. Official State Gazette (BOE). Civil Protection Code and consolidated legislation relating to chemical risk and major accidents.

Last content review: August 2026.