L’esplosione è un evento infortunistico che, pur presentandosi con una limitata frequenza nei luoghi di lavoro, manifesta un’efficacia notevole nel determinare gravi lesioni ai lavoratori esposti. In base alla Direttiva Europea 1999/92/CE, la valutazione del rischio industriale è obbligatoria per ogni sito di produzione. Ma quali elementi rappresentano un rischio esplosivo? Come agire per anticipare i rischi legati all'esplosione e quali sono gli obblighi?
Che cos'è un ambiente a rischio esplosivo?
Quando parliamo di livello di pericolo di un sito industriale, spesso si pensa al regolamento ATEX (ATmosphère EXplosive - ovvero atmosfera esplosiva), nato in seguito alle direttive europee 1999/92/CE e 2014/34/UE.
La direttiva ATEX 99/92/CE è stata recepita in Italia con DLgs 233/03, entrato in vigore il 10 Settembre 2003.
Il successivo DLgs 81/08 del 9 Aprile 2008 (in particolare il titolo XI- Protezione da atmosfere esplosive) e il suo aggiornamento (DLgs 106/2009 del 3/08/09, in vigore dal 20 Agosto) hanno poi superato il DLgs 233/03. L'insieme di queste direttive defiscono le caratteristiche di un edificio a rischio esplosione.
Come sono classificati gli edifici a rischio?
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Le zone ATEX
Il rischio esplosivo è definito in base alla concentrazione di combustibili (gas, vapori o polveri) e alla ventilazione dell’area. Obbedendo a un duplice scopo, le classificazioni ATEX delimitano gli spazi in base al livello di rischio che corrono e definiscono il materiale e le attrezzature appropriate all’ambiente pericoloso.
| 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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Le soglie Seveso
Altre strutture industriali, come i siti Seveso, sfruttano sostanze o composti chimici potenzialmente esplosivi. In caso di incidenti, ne derivano catastrofi sanitarie ed ecologiche (inquinamento dell’aria e dell’acqua).
Dei circa 1.150 stabilimenti a rischio di incidente rilevante, il 25% circa è concentrato in Lombardia; regione che, assieme ad Emilia Romagna, Veneto e Piemonte, comprende oltre il 50% degli stabilimenti pericolosi. I siti Seveso a “soglia bassa“ presentano un rischio di incidenti rilevante, mentre i siti Seveso a “soglia alta“ presentano un alto rischio di incidente rilevante. Questa classificazione si definisce secondo il livello di pericolosità, la natura e il tonnellaggio delle sostanze o associazioni di sostanze presenti nel sito. L’Allegato 1 della direttiva Seveso III categorizza per sostanza il tonnellaggio autorizzato dalla soglia. Altrimenti, lo strumento on line Seveso III , permette di calcolare e definire lo status di Seveso.
La direttiva europea 82/501/CEE chiamata Seveso deriva dal disastro chimico avvenuto in Italia nel 1976 nell’area di Seveso. Il suo scopo è identificare il livello di rischio associato alle attività industriali e rendere quanto più è possibile sicuri i siti interessati. Il testo originario è stato rinforzato dalla direttiva Seveso II (96/82/CE) che è stata a sua volta abrogata dalla direttiva 2012/18/UE, chiamata Seveso III. L'Italia l'ha recepita nel proprio ordinamento giuridico con il decreto legislativo n°105 del 26 giugno 2015, che ha integralmente abrogato i precedenti D.Lgs. n. 334/1999 e 238/2005.
Analizzare i pericoli per stabilire una gestione globale dei rischi
La direttiva europea 1999/92 /CE stabilisce i requisiti minimi in materia di sicurezza degli ambienti a rischio esplosivo. Il suo scopo principale è di proteggere i lavoratori che sono soggetti a questi rischi. I datori di lavoro devono adottare misure precauzionali e assicurare che l’ambiente di lavoro prevenga il più possibile i rischi di incidenti industriali.
La Sezione 6, "prevenzione delle esplosioni" del Codice del Lavoro, specifica i vari obblighi delle strutture con potenziale esplosivo. Queste misure includono, tra le altre, la segnalazione e delimitazione delle aree a rischio, l’organizzazione della prevenzione attraverso la formazione specifica dei dipendenti in situazione di emergenza, la notifica presso la SDIS e la stesura del DRPCE (documento relativo alla protezione contro le esplosioni).
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
