The French industrial fabric counts 235,000 companies and weighs 870 billion euros, or 10% of GDP according to the 2016 summary of the General Directorate of Companies (DGE). To comply with the European Directive 1999/92 / EC, the industrial risk assessment is mandatory for each production site. But which elements present an explosive risk? How to act to anticipate the risks associated with an explosion and what are the obligations?
What is an explosive environment?
When we talk about the level of danger of an industrial site, we most often think of the ATEX regulations (ATmosphères EXplosives). It originates from European Directives 1999/92 / EC and 2014/34 / EU. Transposed in the Labor Code by Articles R. 4216-31 and R. 4227-42 to. R. 4227-54 and the Environmental Code by Decree 2015-799 of 1 July 2015, they define the characteristics of a building at risk of explosive.
How are buildings at risk categorized?
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ATEX zones
Explosive risk is defined according to the concentration of fuels (gas, vapors or dust) and the ventilation of the area. With a double vocation, the ATEX classifications delimit the spaces according to the level of risk incurred and define the material and the equipments adequate to the dangerous environment.
| Environnement ATEX | Fréquence annuelle de l’atmosphère explosive | Gaz, vapeurs ou liquides combustibles (G pour Gaz) | Poussières combustibles (D pour Dust) | Catégorie d’appareils autorisés (EN 60079-0) |
|---|---|---|---|---|
| Danger permanent ou fréquent | Supérieur à 1000 heures | Zone 0 | Zone 20 | 1D ou 1G |
| Danger occasionnel | Compris entre 10 et 1000 heures | Zone 1 | Zone 21 | 2D ou 2G * |
| Danger rare ou accidentel | Inférieur à 10 heures | Zone 2 | Zone 22 | 3D ou 3G ** |
* NB : la catégorie 1 est aussi applicable
** NB : les catégories 1 ou 2 sont aussi applicables
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The Seveso thresholds
Other industrial structures, such as Seveso sites, exploit potentially explosive chemical substances or mixtures. In the event of an accident, the result is health and ecological disasters (air and water pollution). In France, there are 1364 Seveso sites of which 746 qualify as high threshold. The “low threshold” Seveso sites present a major accident risk while the “high threshold” Seveso sites present a high risk of major accidents. This level is defined according to the level of dangerousness, the nature, and the tonnage of substances or associations of substances present on the site. Annex 1 of the Seveso 3 Directive categorises by substance the tonnage authorized by threshold. Otherwise, the online tool Seveso 3 set up by the Ministry of Ecological and Solidarity Transition, allows to calculate to define the Seveso status.
The Seveso European Directive 82/501 / EEC originates from the 1976 Italian chemical disaster of the same name. It aims to identify the level of risk associated with industrial activities and to secure as much as possible the sites concerned. This original text was reinforced by the Seveso 2 Directive (96/82 / EC) itself repealed by Directive 2012/18 / EU, known as Seveso 3. Transposed into French law in 2015, decrees N ° 2014-284 and No. 2014-285.
Analyze the dangers to establish an overall control of the risks
European Directive 1999/92 / EC establishes the minimum requirements for the safety of explosive environments. Its main purpose is to protect workers who are subject to these risks. Employers must take precautionary steps and ensure that the work environment anticipates the risks of industrial accidents as much as possible.
Section 6: “explosion prevention” of the Labor Code specifies the various obligations of structures with explosive potential. These approaches include, among others, the signaling and demarcation of risk areas, the organization of prevention through specific training for employees in emergency situations, the notification to the SDIS and the drafting of the DRPCE (document related to explosion protection).
A key document, its drafting and updates require the inventory of substances on the site and an analysis of the flammability and explosivity risks. The CarAtex database is a valuable tool, it synthesizes in two independent bases the physicochemical characteristics and behaviors of the substances according to their nature. The INRS and the German equivalent authority, the DGVU, establish its databases intended, among others, for ATEX structures.
Conformity and required marking of protective devices
European Directive 2014/34 / EU harmonises the legislation of the member states concerning devices and protective systems intended for use in potentially explosive atmospheres. This European text has been transposed into French law by Decree No. 2015-799.
Section 7: “Compliance of devices and protective systems intended for use in potentially explosive atmospheres” integrated in the environmental code, standardizes the criteria of the protection systems. Protective materials must meet a number of standard criteria, such as CE and EX markings. They must always be accompanied by a written EU declaration of conformity from the manufacturer.
Art. R. 557-7-1: “For the purposes of this section: Protection systems: Devices, other than components of appliances, whose function is to stop incipient explosions or to limit the area immediately affected by an explosion and which are made available separately on the market as autonomous systems “
What are the factors of explosive risk?
The six simultaneous conditions that form an explosion are schematized here in the form of a hexagon. As soon as one of the conditions is evicted, the risk of explosion becomes zero. The source of inflammation is one of the factors that can take many aspects and of which we sometimes suspect little origin. Flames, sparks, electrostatic discharges, lightning, overheating of a faulty appliance or static electricity can trigger the explosion phenomenon. If we remove this activation energy, we observe that the 5 other factors are all present and daily in the ATEX environment.
The presence of dust or gas is related to the activity of the farm (cereals, wood, sugars or residues of inorganic fine particles such as aluminum) or the storage of a substance (nitrogen, alcohol, solvent, oxygen under pressure, liquefied gases such as propane or chlorine). This factor as well as the presence in suspension of a fuel is constantly present in the environment, just as the explosive oxidizer which is air and more specifically oxygen (O2). Containment in a confined space is specific to the industrial site, it is an immutable and aggravating factor. It creates the pressure effect and forces the increased gas volume to expand. The explosive domain defines the concentration thresholds for oxygen and fuels suitable for explosion. It frames the LEL (Lower Explosive Limit) phenomena too fuel-poor to explode and the LSE (Upper Explosive Limit) when the fuel rate is too rich to explode.
How to prevent the risk according to the nature of the fuels?
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Dust risks:
Whether of organic origin, conversely inorganic or metallic, the accumulated dust presents a very high explosive risk when they come into contact with the superheated air. Fine-particle dust such as flour, aluminum powders or powdered milk are very combustible substances when the factors conducive to an explosion are combined.
Atmospheres that present dust also increase the risk of secondary explosion. This phenomenon is common, often more destructive and difficult to control. Dust accumulated on horizontal surfaces is stirred by the primary explosion. This movement generates a new cloud of dust in suspension ready to ignite in turn.
To reduce the risk of explosion, it is recommended to increase the particle size of the dust. This is possible when the materials are raw materials, such as plastic pellets for injection molding operations. But when the farm produces pulverulent waste or requires that the exploited substance be very fine, such as flour, it is not possible to increase the milling. Not all industries can implement this preventive solution.
In the article on the prevention of dust explosion and explosion protection measures, the INRS notes in the summary opposite, prevention measures and protections to put in place to avoid these scourges.
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Risks related to gases, vapors and solvents:
Flammable substances and mixtures in the liquid or gaseous state are the fuels that cause gas explosion phenomena. On the same principle as for dust-related explosions, removing one of the 6 factors from the explosion hex eliminates the risk of explosion. A sharp analysis of the flammability characteristics and thresholds of the gases present or likely to be produced by the activity (such as methane) makes it possible to limit the risk. Removing potential sources of ignition is also a way of anticipating damage. However the diversity of sources makes this factor difficult to master. The failure of a machine that causes a spark or electrostatic discharge from lightning can not always anticipate. The effects of exposure should also be limited by partitioning the areas to prevent the spread of gas and fire.
The article on the risks of gas explosion – prevention and protection (2) relayed by the website “Techniques de l’Ingénieur”, states:
“[…] The protection of the loudspeakers against the effects of gas explosions is based on the installation of explosion vents to reduce the explosion pressure to a value compatible with the mechanical strength of the installations. […]”
Vent, the absolute weapon of anti-explosion prevention:
Industrial explosions, whether the initial fuel is dust or a substance in the gaseous state, cause considerable damage. We keep in mind the catastrophes such as the explosion of the chemical plant Azote de France (AZF) of Toulouse on September 21, 2001 or the explosion of the silo of cereals of Blaye of August 20, 1997. The assessments and losses are very heavy and the structures of buildings are destroyed. The preventive solution advanced by the techniques of the engineer as well as the experts of the INRS for all types of explosions remains the explosion-proof vent. It detects pressure increases inside the building in order to release the overpressure and thus suppresses the blast effect and the blast.
Explovent® explosion-proof vents are the only explosion panels that provide the building structure with in situ and non-destructive testing. Explovent® is reusable and without prior maintenance, thanks to a unique and patented mechanism. Unlike conventional explosion vents or rupture discs, Explovent® does not cause accidents related to the high-speed discharge projection of the outlet during pressure relief. Explovent® offers façade or roof solutions suitable for all building configurations.
CS develops unique safety and security devices designed to provide individuals and works with maximum security. If you wish to carry out a study of your risk environment, contact us, one of our specialists will guide you in your needs analysis.
(1) Source : INRS, Caractéristiques d’inflammabilité et d’explosivité des poussières combustibles
(2) Source : www.techniques-ingenieur.fr, risque d’explosion de gaz- Prévention et protection, Jean Louis GUSTIN, publié le 10 aout 2016
