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Gas detection in SEVESO sites

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In France, there are more than 1,300 establishments classified as SEVESO. This means that these are high-risk industrial sites (risk of explosion, fire, leakage of toxic substances into the air or water), where a high level of prevention must be maintained. They represent 10% of the SEVESO sites in Europe.

From the origin of the term to its current meaning, we will discuss in this article the different risks of SEVESO sites and the appropriate safety and prevention measures.


SEVESO: origin and meaning

SEVESO is first and foremost the name of a city in Italy that suffered an incident in 1976. An explosion without human damage, but which caused significant air pollution. A real shock for the surrounding populations, this incident aroused many emotions. It was after this event that the European SEVESO directives were put in place.

In 1982, Europe put in place the SEVESO 1 directive, which requires the State to identify sites at risk and to list the hazardous materials used. This directive also requires the implementation of protection measures for the environment and the population.

From 1992 to 2015, the SEVESO directive evolved, with the aim of better anticipating risks.

For example, the explosion of the AZF factory in Toulouse on September 21, 2001, led to the drafting of the Risk Law of July 30, 2003. This disaster, the most serious industrial disaster in France since the end of the Second World War, allowed the establishment of the prevention of technological and natural risks and the repair of damage.

The latest directive of July 4, 2012, known as SEVESO 3, came into force on June 1, 2015.

How is a SEVESO 3 site defined?

As soon as a site produces or possesses hazardous materials for the environment, it will be subject to SEVESO regulations, which will make it possible to identify and anticipate the risks of accidents. An establishment will be classified SEVESO 3 according to the quantity of hazardous materials it possesses.

There are two types of establishments:

  • SEVESO low threshold sites: they present relatively low risks because they can be controlled.
  • high threshold SEVESO sites: they present significant risks of accidents, which could have serious consequences. This is why they must comply with much stricter regulations, particularly with the existence of emergency plans. Their safety must be taken very seriously, as well as the information of the surrounding population, because they can also be in danger from risks of explosion or environmental pollution.

Identify and prevent risks

There are 4 main risks at SEVESO sites: the risk of fire, the risk of explosion, the toxic risk and the ecotoxic risk.


Security measures

SEVESO sites must establish a hazard study in order to draw up accident prevention and management plans. This study must be carried out every 5 years for high threshold sites in order to prevent the occurrence of a major accident.

There are three main emergency plans, which are :

  • The Internal Operation Plan (POI): It is necessarily triggered first, at the initiative of the company. This plan is drawn up by the person in charge of the SEVESO site, with the aim of controlling the disaster within his establishment.
  • The Particular Intervention Plan (PPI): It can be triggered by the prefect, if the consequences of the incident exceed the limits of the SEVESO high threshold site. The plan is drawn up by the prefecture. Its purpose is to identify the means and actors that will ensure the protection of the population. It gives instructions in the event that the emergency plan is triggered.
  • The Technological Risk Prevention Plan (PPRT): This plan is set up to protect the population. Indeed, it is imperative that the local companies concerned, close to one or more SEVESO sites, be informed of their exposure to risk. The PPRT represents, in the form of zoning, different zones, and the guidelines to follow for each one.

There are 2 main types of zones:

  • red zones: building ban, expropriation, etc.
  • blue zones: authorization of new constructions under condition, safety obligation for existing activities, etc.

Fire prevention

The training provided to employees must enable them to acquire the right reflexes to protect themselves in the event of an alert and to play an active role (securing posts, managing the gathering, closing ranks, etc.). It is important to define the roles and functions of each person and, as far as possible, to assign only one action per person. The organization put in place for the fire hazard can serve as an example to follow.

Seismic prevention

Sites with a high seismic risk must implement a visit plan. The purpose of these visits will be to examine earthquake-critical equipment, which could be the cause of serious consequences.

Control of urbanization

In the past, major industrial disasters (3 main ones: Seveso in 1976, Bhopal in 1984, and AZF in 2001) have shown us that it is essential to inform the population about the risks of accidents.

The three major disasters mentioned above caused a lot of damage. These could have been reduced if the population had been informed of the risks and the meaning of the alarm. After all this, we know today that communication between SEVESO sites and the surrounding population is essential. Everyone must know how to react if the siren goes off.

Industrial accidents and the environment

Most accidents occur in establishments classified as hazardous (in particular SEVESO classified sites), such as waste and wastewater activities, the chemical and pharmaceutical industries, food processing and agriculture.

Accidents are generally caused by:

  • Hazardous material releases (68% of cases)
  • Fires (54% of cases)
  • Explosions

The main causes of accidents are similar to those of previous years: they are related to the organization of controls, the choice of protective equipment, and the identification of risks.



As the MASE is a certification for the improvement of Health and Safety at Work and the respect of the environment, it may be necessary to have the MASE certification to intervene on a SEVESO site.

This certification allows both the intervening company and the user company to have a common language in terms of Health, Safety and Environment in companies. Indeed, as SEVESO sites are generally MASE certified, it is preferable for them to work with companies that are also certified.

In addition, certifications such as ISO 9001, 14001 or 45001 are also recognized by SEVESO sites.

Individual protection

protection individuelle

Workers on SEVESO sites, as well as people who have to intervene on this type of site, must be equipped with personal protection. This protection varies depending on the site and the analysis of the risks.

Generally, we will find :

  • A gas detection system: in the chemical industry and particularly in SEVESO classified sites, the presence of gas, sometimes toxic, is frequent. It is essential to set up a gas detection system, either portable or fixed.
  • A respiratory protection device: in view of the toxic risk present in SEVESO sites, it is obvious that respiratory protection is a major element of the protective equipment.
  • A fall protection device: depending on the type of workstation, it may be necessary for the worker to be equipped with a fall protection device.

To deal with risks at SEVESO sites, several elements are important:

  • Knowledge of the risk by the company
  • The organization and information of the urbanization
  • Management of the public and populations

In addition, it is important to be properly equipped, to master :

  • Toxic risk: fixed (beacon, central, etc.) or portable gas detection
  • Emergency evacuation: escape mask or filtering mask, etc.
  • Interventions: Self-contained breathing apparatus (SCBA)

The maintenance of this protective equipment is also essential.

Titre du push

Protective equipment on SEVESO sites