SIST EN 12753:2005

Thermal cleaning systems for exhaust gas from surface treatment equipment - Safety requirements

1.1   This document is applicable to thermal cleaning systems for exhaust gas from surface treatment equipment/systems as given below in which the concentration of exhaust gas to be cleaned (for the purpose of this document, named "process gas") at the inlet to the thermal cleaning system is safely limited within the concentration ranges given in 5.2.1.2.
Surface treatment equipment includes:
-   dryers according to EN 1539, curing equipment;
-   flash-off areas;
-   coating plants (e.g. closed spray booths, open fronted spray booths);
-   machines using flammable solvents for the pre-treatment and cleaning of products or equipment (e.g. barrels, tins, cans or containers);
-   related solvent handling equipment.
This document deals only with the significant hazards from fire and explosion as listed in Clause 4, when used as intended and under the conditions foreseen by the manufacturer.
The types of thermal cleaning systems covered in this document are
-   direct combustion, and
-   catalytic combustion
(see definitions in 3.1.1 and 3.1.2).
This document shall be used in conjunction with the relevant requirements of EN 746-1 and EN 746-2.
For the purpose of this document a thermal cleaning system for process gas contains the following components: fan(s), heat exchanger, process space, main and supporting burner, injection system, power driven dampers, control and power circuits joined together for the processing of flammable substances, predominantly volatile organic compounds, by effecting oxidation.
NOTE    Thermal cleaning equipment is usually integrated with systems as covered by e.g. EN 1010, EN 1539, EN 12215, prEN 12921-1 or prEN 12921-3.
1.2   This document is not applicable to:
-   thermal paint removal systems;
-   pyrolytic systems.
1.3   This document is not applicable to thermal cleaning systems which are manufactured before the date of publication of this document by CEN.

Thermische Reinigungssysteme für Abluft aus Anlagen zur Oberflächenbehandlung - Sicherheitsanforderungen

1.1   Diese Europäische Norm gilt für thermische Reinigungssysteme für Abluft aus Anlagen/Systemen zur Oberflächenbehandlung wie im Folgenden angegeben, bei denen die Konzentrationen der zu reinigenden Abluft (für die Zwecke dieser Europäischen Norm als "Prozessgas" bezeichnet) am Einlass zum thermischen Reinigungssystem sicher auf die in 5.2.1.2 angegebenen Konzentrationsbereiche beschränkt ist.
Anlagen zur Oberflächenbehandlung sind:
3   Trockner nach EN 1539, Aushärtungseinrichtungen,
3   Abdunstbereiche,
3   Beschichtungsanlagen (z. B. Spritzstände und Spritzkabinen),
3   Anlagen zur Vorbehandlung und Reinigung mit brennbaren Lösemitteln von Produkten oder Einrichtungen (z. B. für Dosen, Fässer, Gebinde oder Container),
3   Zugehörige Lösemitteltransporteinrichtungen.
Diese Europäische Norm behandelt nur die signifikanten Brand- und Explosionsgefährdungen wie in Abschnitt 4 aufgeführt, bei bestimmungsgemäßer Verwendung unter den vom Hersteller vorgesehenen Bedingungen.
In dieser Europäischen Norm werden folgende Arten der thermischen Reinigung behandelt:
3   direkte Verbrennung,
3   katalytische Verbrennung.
(siehe Definitionen in 3.1.1 und 3.1.2).
Diese Europäische Norm muss in Übereinstimmung mit den entsprechenden Anforderungen in EN 746-1 und EN 746-2 verwendet werden.
Für die Zwecke dieser Europäischen Norm besteht ein thermisches Reinigungssystem aus folgenden Komponenten: Ventilator(en), Wärmetauscher, Reaktionszone, Haupt- und Hilfsbrenner, kraftbetriebene Drosselklappen, Steuer- und Energiekreise, die zusammengefügt wurden, um die Oxidation von brennbaren Stoffen, vorwiegend flüchtigen organischen Verbindungen, zu bewirken.
ANMERKUNG   Thermische Reinigungssysteme sind im Allgemeinen mit Systemen verbunden, die z. B. von prEN 1010-1, EN 1539, EN 12215, EN 12921-1 und EN 12921-3 abgedeckt werden.

Systemes d'épuration thermique de l'air extrait des installations de traitement de surface - Prescriptions de sécurité

1.1   La présente Norme européenne s'applique aux systemes d'épuration thermique de l'air extrait des équipements/systemes de traitement de surface comme indiqué ci-dessous, dans lesquels la concentration d'air extrait a épurer (pour le propos de la présente Norme européenne, appelé " air extrait ") a l'entrée du systeme d'épuration thermique est limitée en terme de sécurité aux plages de concentrations données au 5.2.2.2.
Les équipements de traitement de surface comprennent :
-   séchoirs (étuves) en accord avec l'EN 1539, équipements de cuisson ;
-   zones de pré-séchage ;
-   installations d'application (par exemple, cabines fermées d'application de peinture, cabines d'application a ouverture frontale) ;
-   machines pour le prétraitement et le nettoyage utilisant des solvants inflammables (par exemple, tonneaux, boîtes ou conteneurs) ;
-   équipement de transport de solvants.
La présente Norme européenne ne traite que des phénomenes dangereux significatifs engendrés par les systemes d'épuration thermique (incinérateurs), énumérés dans l'Article 4, lorsqu'ils sont utilisés normalement et dans les conditions prévues par le constructeur.
Les types de systemes d'épuration thermique couverts par la présente Norme européenne sont :
-   a combustion directe ; et
-   a combustion catalytique ;
(voir définitions 3.1.1 et 3.1.2).
La présente Norme européenne s'applique conjointement avec les prescriptions significatives de l'EN 746-1 et l'EN 746-2.
Pour le propos de la présente Norme européenne un systeme d'épuration thermique pour air extrait comprend les composants suivants : ventilateur(s), échangeur thermique, espace de réaction, bruleur principal et occasionnel, systeme d'injection, registres motorisés, circuits d'alimentation et de commande reliés ensembles pour le processus de substances inflammables, composés organiques volatiles de façon prédominante, par oxydation.

Sistemi za termično čiščenje plinov, odsesanih iz naprav za površinsko obdelavo - Varnostne zahteve

General Information

• Status: Withdrawn
• Publication Date: 30-Jun-2005
• Withdrawal Date: 18-Jul-2010
• ICS: 13.040.40 - Stationary source emissions
• ICS: 25.220.01 - Surface treatment and coating in general
• Technical Committee: VSN - Safety of machinery
• Current Stage: 9900 - Withdrawal (Adopted Project)
• Start Date: 07-Jul-2010
• Due Date: 30-Jul-2010
• Completion Date: 19-Jul-2010
• Directive: 94/9/EC - Directive 94/9/EC of the European Parliament and the Council of 23 March 1994 on the approximation of the laws of the Member States concerning equipment and protective systems intended for use in potentially explosive atmospheres
• Directive: 98/37/EC - Machinery
• Mandate: M/079 - Mandate to CEN and CENELEC for standardization in the field of machines
• Mandate: M/BC/CEN/92/46 - Standardization mandate assigned to CEN/CENELEC concerning equipment and protective systems intended for use in potentially explosive atmospheres
• Ref Project: EN 12753:2005 - Thermal cleaning systems for exhaust gas from surface treatment equipment - Safety requirements

Relations

• Consolidated By: SIST EN 12753:2005+A1:2010 - Thermal cleaning systems for exhaust gas from surface treatment equipment - Safety requirements
• Effective Date: 18-Jan-2023
• Consolidated By: SIST EN 12753:2005+A1:2010 - Thermal cleaning systems for exhaust gas from surface treatment equipment - Safety requirements
• Effective Date: 19-Jan-2023
• Replaced By: SIST EN 12753:2005+A1:2010 - Thermal cleaning systems for exhaust gas from surface treatment equipment - Safety requirements
• Effective Date: 01-Oct-2010

Standards Content (Sample)

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Thermal cleaning systems for exhaust gas from surface treatment equipment - Safety requirementsSystemes d'épuration thermique de l'air extrait des installations de traitement de surface - Prescriptions de sécuritéThermische Reinigungssysteme für Abluft aus Anlagen zur Oberflächenbehandlung - SicherheitsanforderungenTa slovenski standard je istoveten z:EN 12753:2005SIST EN 12753:2005en25.220.0113.040.40ICS:SLOVENSKI
STANDARDSIST EN 12753:200501-julij-2005







EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 12753May 2005ICS 13.040.40; 25.220.01English versionThermal cleaning systems for exhaust gas from surfacetreatment equipment - Safety requirementsSystèmes d'épuration thermique de l'air extrait desinstallations de traitement de surface - Prescriptions desécuritéThermische Reinigungssysteme für Abluft aus Anlagen zurOberflächenbehandlung - SicherheitsanforderungenThis European Standard was approved by CEN on 21 March 2005.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the Central Secretariat or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2005 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 12753:2005: E



EN 12753:2005 (E) 2 Contents Page Foreword.3 0 Introduction.4 1 Scope.5 2 Normative references.6 3 Terms and definitions.7 4 List of significant hazards.9 4.1 General.9 4.2 Fire and explosion hazards.9 4.3 Hazards generated by residual process gases.12 5 Safety requirements and/or protective measures.12 5.1 General.12 5.2 Fire and explosion.12 5.3 Requirements against hazards generated by residual process gas.19 6 Verification of the safety requirements and / or protective measures.19 7 Information for use.20 7.1 General.20 7.2 Instruction handbook.20 7.3 Marking.22 Annex A (informative)
Schematic views of thermal cleaning systems.23 Annex B (informative)
Temperature dependency of LEL.27 Annex C (informative)
Operating parameters, conditions for use and measurement methods.31 Annex D (informative)
Guidelines for thermal cleaning systems operating at increased concentrations.32 Annex E (informative)
References to national exposure limit values.34 Annex F (normative)
Classification of material's reaction to the fire — national standards.35 Annex G (informative)
Relation between categories and zones.36 Annex ZA (informative)
Relationship between this European Standard and the Essential Requirements of EC Directive 98/37/EC.37 Bibliography.38



EN 12753:2005 (E) 3 Foreword This European Standard (EN 12753:2005) has been prepared by Technical Committee CEN/TC 271, "Surface treatment equipment — Safety ", the secretariat of which is held by DIN. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by November 2005, and conflicting national standards shall be withdrawn at the latest by November 2005. This European Standard has been prepared under a mandate given to CEN by the Commission of the European Communities and the European Free Trade Association, and supports essential requirements of EU Directive(s). For relationship with EU Directives, see informative Annex ZA, which is an integral part of this European Standard. This European Standard is part of a set of standards devoted to the health and safety requirements of installations for the application and drying of coating materials. The attention of the reader is drawn to the fact that compliance with this European Standard does not waive the obligation to comply with the regulations governing installations categorised for environmental protection which also deal with the risks of nuisance to the surroundings such as noise emitted outside the building, odours, pollution. NOTE Although a thermal cleaning system, as an integral whole, formally does not fall under the scope of the ATEX Directive 94/9/EC, the standard is based upon a fundamental risk analysis according to this directive. This European Standard includes a Bibliography. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.



EN 12753:2005 (E) 4 0 Introduction This European Standard is a type C standard as stated in EN ISO 12100. The machinery concerned and the extent to which hazards, hazardous situation and events are covered are indicated in the scope of this European Standard. When provisions of this type C standard are different from those which are stated in type A or B standards, the provisions of this type C standard take precedence over the provisions of the other standards, for machines that have been designed and built according to the provisions of this European Standard.



EN 12753:2005 (E) 5 1 Scope 1.1 This European Standard is applicable to thermal cleaning systems for exhaust gas from surface treatment equipment/systems as given below in which the concentration of exhaust gas to be cleaned (for the purpose of this European Standard, named "process gas") at the inlet to the thermal cleaning system is safely limited within the concentration ranges given in 5.2.2.2. Surface treatment equipment includes:  dryers according to EN 1539, curing equipment;  flash-off areas;  coating plants (e.g. closed spray booths, open fronted spray booths);  machines using flammable solvents for the pre-treatment and cleaning of products or equipment (e.g. barrels, tins, cans or containers);  related solvent handling equipment. This European Standard deals only with the significant hazards from fire and explosion as listed in Clause 4, when used as intended and under the conditions foreseen by the manufacturer. The types of thermal cleaning systems covered in this European Standard are  direct combustion, and  catalytic combustion (see definitions in 3.1.1 and 3.1.2). This European Standard applies in conjunction with the relevant requirements of EN 746-1 and EN 746-2. For the purpose of this European Standard a thermal cleaning system for process gas contains the following components: fan(s), heat exchanger, process space, main and supporting burner, injection system, power driven dampers, control and power circuits joined together for the processing of flammable substances, predominantly volatile organic compounds, by effecting oxidation. NOTE
Thermal cleaning equipment is usually integrated with systems as covered by e.g. EN 1010-1, EN 1539, EN 12215, EN 12921-1 or EN 12921-3. 1.2 This European Standard is not applicable to:  thermal paint removal systems;  pyrolytic systems. 1.3 This European Standard is not applicable to thermal cleaning systems which are manufactured before the date of publication of this document by CEN.



EN 12753:2005 (E) 6 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 746-1, Industrial thermoprocessing equipment — Part 1: Common safety requirements for industrial thermoprocessing equipment EN 746-2, Industrial thermoprocessing equipment — Part 2: Safety requirements for combustion and fuel handling systems EN 954-1:1996, Safety of machinery — Safety related parts of control systems — Part 1: General principles for design EN 1127-1:1997, Explosive atmospheres — Explosion prevention and protection — Part 1: Basic concepts and methodology EN 13463-1:2001, Non-electrical equipment for potentially explosive atmospheres — Part 1: Basic method and requirements EN 13463-5, Non-electrical equipment intended for use in potentially explosive atmospheres — Part 5: Protection by constructional safety “c” prEN 14986, Design of fans working in potentially explosive atmospheres EN 50015, Electrical apparatus for potentially explosive atmospheres — Oil immersion "o" EN 50017, Electrical apparatus for potentially explosive atmospheres — Powder filling "q" EN 50020, Electrical apparatus for potentially explosive atmospheres — Intrinsic safety "i" EN 60079-0:2004, Electrical apparatus for explosive gas atmospheres — Part 0: General requirements (IEC 60079-0:2004) EN 60079-1:2004, Electrical apparatus for potentially explosive atmospheres — Part 1: Flameproof enclosures "d" (IEC 60079-1:2003) EN 60079-2, Electrical apparatus for explosive gas atmospheres — Part 2: Pressurized enclosures “p” (IEC 60079-2:2001) EN 60079-7, Electrical apparatus for explosive gas atmospheres — Part 7: Increased safety “e” (IEC 60079-7:2001) EN 60079-15, Electrical apparatus for explosive gas atmospheres - Part 15: Type of protection "n" (IEC 60079-15:2001, modified) EN 60079-18, Electrical apparatus for explosive gas atmospheres — Part 18: Construction test and marking of type of protection encapsulation "m" electrical apparatus (IEC 60079-18:2004) EN 60079-25:2004, Electrical apparatus for explosive gas atmospheres — Part 25: Intrinsically safe systems (IEC 60079-25:2003) EN 60204-1:1997, Safety of machinery — Electrical equipment of machines — Part 1: General requirements (IEC 60204-1:1997) EN 60519-1, Safety in electroheat installations — Part 1: General requirements (IEC 60519-1:2003)



EN 12753:2005 (E) 7 EN ISO 12100-1:2003, Safety of machinery — Basic concepts, general principles for design — Part 1: Basic terminology, methodology (ISO 12100-1:2003) EN ISO 12100-2-2003, Safety of machinery — Basic concepts, general principles for design — Part 2: Technical principles (ISO 12100-2:2003) 3 Terms and definitions For the purposes of this European Standard, the terms and definitions given in EN ISO 12100-1:2003 and the following apply. 3.1 thermal cleaning system assembly of linked components and machines such as fan(s), heat exchanger, process space, heating device (burner), power driven dampers, control and power circuits joined together for the processing of flammable substances, predominantly volatile organic compounds, by effecting oxidation. In a thermal cleaning process gases containing flammable substances are heated to a sufficient temperature in order to oxidise the flammable fraction 3.1.1 direct combustion direct combustion of solvents in flames or high temperature atmosphere 3.1.1.1 direct regenerative combustion direct combustion of preheated process gas, where the heat recovery of the storage media of the thermal reactor heated by thermal combustion is used (regenerative heat exchange) 3.1.1.2 direct recuperative combustion direct combustion of preheated process gas, where the heat exchange (without heat storage) takes place between "cold" process gas and hot exhaust gas of the thermal combustion according to the (cross) reverse flow principle (recuperative heat exchange) 3.1.2 catalytic combustion combustion of solvents with catalysts 3.1.2.1 catalytic regenerative combustion catalytic combustion of preheated process gas, where the heat recovery of the storage media of the thermal reactor heated by thermal combustion is used (regenerative heat exchange) 3.1.2.2 catalytic recuperative combustion direct combustion of preheated process gas, where the heat exchange (without heat storage) takes place between "cold" process gas and hot exhaust gas of the thermal combustion according to the (cross) reverse flow principle (recuperative heat exchange) 3.2 process gas for the purpose of this European Standard process gas is defined as the exhaust gas from the surface treatment equipment/system and may contain a mixture of air and flammable substances. The process gas is the gas supplied to the thermal cleaning system for effecting of oxidation. It may include fumes, inert gases as well as solid and/or liquid particles which may trigger condensation and lead to deposits. Process gas may also include recirculated exhaust gas from the thermal cleaning system



EN 12753:2005 (E) 8 3.3 process space volume within the thermal cleaning system in which the flammable substances are oxidised 3.4 flammable substances predominantly volatile organic compounds (VOC's), which can include gases, vapours, liquids, solids, or mixtures of these, able to undergo an exothermic reaction with air when ignited EXAMPLE  Solvents, which are flammable or extremely difficult to ignite (no flash point, but an explosion range), for example partly halogenated hydrocarbons,  most coating materials. See 3.1 of EN 1127-1:1997. 3.5 solvents liquids, single or blended, volatile under specific temperature conditions [2.49 of EN 971-1:1996] NOTE Solvent vapours are usually part of the exhaust gases of surface treatment equipment (for the purpose of this European Standard named process gas (see 3.2)). EXAMPLES  Aldehydes, alcohol, hydrocarbons, esters, ketones, mineral oils, as well as mixtures containing these substances.  Printing inks, varnishes, lacquers etc., used as coating materials containing such solvents. Solvents are also used as cleaning or washing agents. 3.6 lower explosion limit (LEL) lower concentration limit of the explosion range NOTE Explosion limits are the limits of the explosion range. Explosion range is the range of the concentration of flammable substances in air, over which an explosion can occur. See 3.7, 3.8 and 3.13 of EN 1127-1:1997. It is recommended to check the data on safety characteristics e.g. in safety data sheets, see Bibliography. 3.7 explosive mixture mixture with air of combustible substances in the form of gases, vapours, mist or dust, in which after ignition has occurred, combustion spreads to the entire unburned mixture NOTE Explosive atmosphere is an explosive mixture under atmospheric conditions, see 3.17 of EN 1127-1:1997. 3.8 hazardous explosive mixture explosive mixture which, if it explodes, causes damage 3.9 forced ventilation (for forced ventilation of the thermal cleaning system) air exchange achieved by fans or by other powered means which directs the process gas to the thermal cleaning system 3.10 recirculation air part of the cleaned process gas from the thermal cleaning system is reintroduced into the system for means of energy saving or other reasons NOTE The reintroduction can take place either in the thermal cleaning system itself (internal recirculation) or in an upstream part of the system, for example a dryer (external recirculation).



EN 12753:2005 (E) 9 3.11 maximum admissible concentration of flammable substances concentration within the total thermal cleaning system, which shall not be exceeded 3.12 minimum exhaust volume flow which corresponds to the maximum admissible quantity or throughput of flammable substances for all specified operating conditions 4 List of significant hazards 4.1 General This clause contains all significant hazards, hazardous situation and events, as far as they are dealt with in this European Standard, identified by risk assessment as significant for one or more, or all types of thermal cleaning systems for process gases included in the scope and which require action to eliminate or reduce the risk. 4.2 Fire and explosion hazards 4.2.1 General Fire and explosion hazards are generated by process gases containing hazardous flammable substances and/or explosive mixtures together with sources of ignition. NOTE 1 These hazards can both occur within the thermal cleaning system and in upstream or downstream equipment. NOTE 2 Examples of upstream equipment are:  dryers;  printing machines;  coating plants/equipment;  press roller washing systems/equipment;  recirculation systems.
Examples of downstream equipment are:  heat recovery systems,  recirculation systems.
Examples of flammable substances are:  solvent vapours;  fuel gases;  condensates;  deposits;  gases released from condensates and/or deposits.
Examples of ignition sources are:  hot surfaces (e.g. of heating systems, of electrical equipment);  heating systems, burners, combustion products;  sparks created by mechanically induced energy (e.g. by fans wheel, bearing);  electrostatic discharges;  electrical sparks;  hot gases or chemical reactions within the system/equipment itself and/or in upstream and downstream equipment components or duct systems due to back-firing.



EN 12753:2005 (E) 10 4.2.2 Hazards of explosive mixtures 4.2.2.1 General Hazards of explosive mixtures are generated from the inside concentration and the mode of operation of both the thermal cleaning system itself and of upstream and downstream equipment. The main causes are listed in 4.2.2.2 to 4.2.2.7. 4.2.2.2 Inlet concentration Hazards of explosive mixtures are generated inside the thermal cleaning system if the concentration of flammable substances at the inlet to the thermal cleaning system is so high that the LEL is exceeded by heating of the process gas within the thermal cleaning system. NOTE Inlet concentration may include the injection of flammable substances. 4.2.2.3 Linking multiple sources to a thermal cleaning system Linking multiple sources of process gases to a common thermal cleaning system without correctly integrating the systems (sources) may generate an explosion hazard due to high concentrations. NOTE Increased concentrations may result from:  failure of one or more of the multiple sources e.g. loss of high volume/low concentration flow;  adding or replacing of sources. 4.2.2.4 Condensates and deposits Condensates and/or deposits which are evaporated and/or thermally decomposed e.g. in ducts and heat exchangers may increase the concentrations of flammable substances. Deposits can also be dusts which may disperse without decomposition to give hazardous explosive mixtures. 4.2.2.5 Insufficient forced ventilation Insufficient ventilation and flow rates within the thermal cleaning system may generate increased concentrations of process gas and form hazardous explosive mixtures. Insufficient ventilation and flow rates e.g. as a result of failure of the frequency control of the fan for the thermal cleaning system may lead to:  insufficient purge before starting the system;  insufficient flow in the system and ducts;  failure of fresh air supply. Ventilation and flow rate may be influenced by:  narrowed channels and/or housing of fan caused by deposits (condensate);  adjustment of control flaps or dampers. 4.2.2.6 Insufficient oxidation In case of thermal cleaning systems recirculating the cleaned process gases in order to reduce the concentrations of flammable substances at the inlet of that system, insufficient oxidation may increase the concentration of flammable substances to such an extent that hazardous explosive mixtures may be generated. Causes for insufficient oxidation can be: a) too low oxygen content of the process gas;



EN 12753:2005 (E) 11 b) too low temperature within the process space; c) insufficient intermixture of supplied process gases within the process space; d) insufficient residence time of flammable substances within the process space; e) reduced catalyst function due to ageing, poisoning or deposits on the active surface. NOTE The ability of the catalyst to allow chemical reactions at reduced temperatures is not a fixed characteristic but decreases during the operation. This decrease of activity may be caused by surface modifications due to the temperature (ageing), blocking of the active centres due to catalyst poisons such as silicone or reduction of the active surface because of dust deposits. 4.2.2.7 Adsorption of flammable substances in catalytic systems Adsorption of flammable substances on the surfaces of catalytic elements can occur, when the catalytic system is operated at temperatures of the incoming gases below the temperature necessary for catalytic reaction. Flammable substances being adsorbed on the surface of catalytic elements may lead to hazardous explosive mixtures, when desorption of the flammable substances takes place because of increased incoming gas temperature or the beginning of an exothermic reaction. NOTE The temperature necessary for catalytic reaction is not a fixed characteristic of the given catalyst but depends on the substance to be converted and may rise because of ageing, poisoning or deposits. 4.2.3 Ignition sources Thermal cleaning systems include equipment components which, because of the required temperatures for oxidation, present ignition sources. Together with hazardous explosive mixtures, these ignition sources may result in explosions. NOTE Other ignition sources can be present in integrated equipment. 4.2.4 Explosion effects Explosions in the thermal cleaning systems may give rise to:  the hazard of burning (e.g. flames, radiation of heat, hot blast waves);  the hazard from ejected parts;  the hazard from release of dangerous substances (e.g. hot gases). 4.2.5 Overheating and fires The thermal cleaning system or equipment components may be damaged due to overheating. Furthermore, fires within the vicinity of the system can be caused by too high temperatures at the outer side of the thermal cleaning system or leakage of hot gases. Overheating may be caused by:  ignition of flammable condensates and/or deposits;  failure of temperature control within the process space;  malfunction of heating system;  failure of damper control systems;



EN 12753:2005 (E) 12  failure of insulation of system components;  leakages;  failure of the control system of the ventilation. 4.2.6 Failure of the control systems Failure of the control system (e.g. faults of software and/or hardware) may lead to:  hazard of unintended start-up or shutdown of the thermal cleaning system;  failure or impairment of forced ventilation resulting in formation of hazardous explosive mixtures. 4.3 Hazards generated by residual process gases The hazard of suffocation and intoxication by residual process gases may exist, when entering a thermal cleaning system during maintenance or inspection. 5 Safety requirements and/or protective measures 5.1 General Machinery shall comply with the safety requirements and/or protective measures of this clause. In addition, the machine shall be designed according to the principles of EN ISO 12100-2 for hazards relevant but not significant which are not dealt with by this European Standard. The requirements for associated fuel combustion and fuel handling systems of thermal cleaning systems shall fulfil the requirements of EN 746-1 and EN 746-2 (see 1.1). Systems to enrich the process gas with flammable substances to optimise the oxidation process if installed, shall fulfil the requirements of 5.2.6 and EN 746-2. Verification of the protective measures detailed in this clause, in most cases, shall be carried out by inspection and/or testing of the function of the equipment during installation and commissioning. 5.2 Fire and explosion 5.2.1 Introduction The design shall take into consideration the presence of all kinds of flammable substances, all potential ignition sources and the interaction between parts of the whole system and combination of these hazards. The control range of the thermal cleaning system shall be designed to suit the whole range of operating conditions. The operating conditions are characterised by e.g. flow rates, solvent concentration, temperatures, physical properties of solvents. 5.2.2 Prevention of hazardous explosive mixtures (Limitation of concentration of flammable substances) 5.2.2.1 General The essential safety requirement for thermal cleaning systems is the limitation of the concentration of flammable substances being fed into them, because generally an ignition source exists during operation.



EN 12753:2005 (E) 13 5.2.2.2 Limitation of inlet concentration The total concentration of flammable substances at the inlet to the thermal cleaning system shall be limited to prevent the LEL being exceeded (see 5.2.6) as a result of its temperature dependency during any preheating before the process gases enter the process space. Limitation of the inlet concentration below the LEL is ensured: a) in cases where the mass content of aromatic hydrocarbons is < 25 % of the total concentration of flammable substances at the inlet, independent of the level of pre-heating temperature, the maximum concentration of those flammable substances is 25 % of LEL (20 °C, 1 013 mbar — see example in B.3.1); or b) in cases where the mass content of aromatic hydrocarbons is ≥ 25 % of the total concentration of flammable substances at the inlet, independent of the level of pre-heating temperature, the maximum concentration of those flammable substances is 20 % of LEL (20 °C, 1 013 mbar — see example in B.3.2); or c) independent of the mass concentration of aromatic hydrocarbons, in systems where the temperature in the heat exchanger does not exceed 450 °C, the maximum concentration of flammable substances is 50 % of LEL (maximum temperature and pressure in the heat exchanger). Table 1—Limitation of the inlet concentration
Maximum temperature in the heat exchanger Mass content of aromatic hydrocarbons Admissible concentration given in % of LEL Reference temperature a) Independent < 25 % 25 % 20 °C b) Independent > 25 % 20 % 20 °C c) 450 °C Independent 50 % Theat exchanger
NOTE 1 The indicated limit values represent the proven findings of scientific studies (see Bibliography) and experiences in the operation of thermal cleaning systems. These findings show that mixtures corresponding to the values indicated in subclauses a), b) and c) do not result in explosive reactions of the flammable substances but an accelerated combustion takes place at temperatures in the region 600 °C. For further information see Bibliography. NOTE 2 For temperature de
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