Bsi bs en 12753 2005 + a1 2010

NORME EUROPÉENNE English Version Thermal cleaning systems for exhaust gas from surface treatment equipment - Safety requirements Systèmes d'épuration thermique de l'air extrait des in

Thermal cleaning

systems for exhaust

gas from surface

treatment equipment —

Safety requirements

ICS 13.040.40; 25.220.01

National foreword

This British Standard is the UK implementation of

EN 12753:2005+A1:2010 It supersedes BS EN 12753:2005 which is withdrawn

The start and finish of text introduced or altered by amendment is indicated in the text by tags Tags indicating changes to CEN text carry the number of the CEN amendment For example, text altered

by CEN amendment A1 is indicated by !"

The UK participation in its preparation was entrusted by Technical Committee MCE/3, Safety of machinery, to Subcommittee MCE/3/8, Thermoprocessing machinery — safety

A list of organizations represented on this subcommittee can be obtained on request to its secretary

This publication does not purport to include all the necessary provisions of a contract Users are responsible for its correct application

Compliance with a British Standard cannot confer immunity from legal obligations.

This British Standard was

published under the authority

of the Standards Policy and

NORME EUROPÉENNE

English Version

Thermal cleaning systems for exhaust gas from surface

treatment equipment - Safety requirements

Systèmes d'épuration thermique de l'air extrait des

installations de traitement de surface - Prescriptions de

This European Standard exists in three official versions (English, French, German) A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the official versions

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom

EUROPEAN COMMITTEE FOR STANDARDIZATION

C O M I T É E U R O P É E N D E N O R M A L I S A T I O N

E U R O P Ä I S C H E S K O M I T E E FÜ R N O R M U N G

Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2010 CEN All rights of exploitation in any form and by any means reserved

worldwide for CEN national Members

Ref No EN 12753:2005+A1:2010: E

Contents

Page

Foreword 3

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 EU Directive 2006/42/EC"" 37

Bibliography 38

Foreword

This document (EN 12753:2005+A1:2010) 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 2010, and conflicting national standards shall be withdrawn at the latest

by November 2010

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights

This document includes Amendment 1, approved by CEN on 2010-04-23

This document supersedes EN 12753:2005

The start and finish of text introduced or altered by amendment is indicated in the text by tags ! "

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, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom

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

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 and hazards generated

by residual process gases 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

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 2, Electrical apparatus for explosive gas atmospheres — Part 2: Pressurized enclosures “p” (IEC 2:2001)

EN 7, Electrical apparatus for explosive gas atmospheres — Part 7: Increased safety “e” (IEC 7:2001)

EN 15, Electrical apparatus for explosive gas atmospheres - Part 15: Type of protection "n" (IEC 15:2001, modified)

60079-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 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

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

 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

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

3.11

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

Examples of downstream equipment are:

 heat recovery systems,

 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

4.2.2 Hazards of explosive mixtures

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;

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

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;

 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

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 concentration given Admissible

in % of LEL

Reference temperature

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 dependence of the LEL, see Annex B For information about types of thermal cleaning systems,

properties of volatile flammable substances and process design see Annex D There are ways to operate thermal cleaning systems safely at higher concentrations than those given by a), b) and c) These types of thermal cleaning systems are not covered by this European Standard This is due to the fact that these conditions for a safe operation depend on the specific design of the thermal cleaning system and cannot be determined in a generally applicable way The risk assessment and the design of such thermal cleaning systems is covered by EN 1127-1 For further information see Annex D

If the limitation of the inlet concentration as given in Table 1 cannot be ensured, the inlet concentration shall be monitored (e.g by FID, FTA or IR-gas detectors) and interlocked with at least one of the following measures:

 damper for diluting of the process gas (e.g by fresh air);

 damper cutting off the process gas;

 damper bypassing the system

NOTE 3 Bypassing may need to apply to additional national environmental regulations

The interlocking shall ensure the operation of the system within the limits given in Table 1

5.2.2.3 Linking multiple sources to a thermal cleaning system

When multiple sources of flammable substances are linked to a common thermal cleaning system then it shall be ensured that the limit value as defined in 5.2.2.2 is not exceeded at the inlet to the thermal cleaning system following the requirements of 5.2.6.1

5.2.2.4 Avoidance of condensates and deposits

Condensates and/or deposits in ducts shall be avoided by:

a) The flow in ducts shall be designed and constructed in such a way that deposits and condensates are avoided

If deposits are possible, provision shall be made for easy inspection and cleaning of the ducts

Deposits can for example occur at abrupt changes in cross-section and direction and can also be influenced by the length of ducts and the flow rate

For ease of cleaning, the ducts and equipment parts (especially the heat exchanger) can for example be provided with ports or facilities for simple disconnection of the duct

b) During operation, except for start-up of the system, the temperature of the ducts, heat exchangers etc shall not be below the dew-point of the process gases passing through them If necessary heat insulation of ducts shall be provided

c) After shutdown of the solvent emitting process the thermal cleaning system and the relevant ductwork has to

be purged to ensure that all residual flammable substances are removed In general, five complete air changes

of the thermal cleaning system and duct will suffice The air flow rate used for purge shall be at least 25 % of the maximum flow

NOTE Further information regarding the frequency of inspection and cleaning requirements are given in Clause 7

5.2.2.5 Prevention of insufficient forced ventilation

Increased concentrations of flammable substances above the admissible level, entering the thermal cleaning system due to insufficient forced ventilation shall be avoided by the following measures:

a) Prior to ignition of the heating system the thermal cleaning system has to be purged to ensure that the concentration of the flammable substances is below 25 % of LEL of the flammable substances

In general, five complete air changes of the thermal cleaning system and duct will suffice The air flow rate used for purge shall be at least 25 % of the maximum flow

b) The forced ventilation shall purge all spaces (systems) of the thermal cleaning system and connected ductwork permanently to avoid exceeding the admissible solvent concentrations Ducts shall be capable of being shut off

at the inlet to the collection duct when they are not in service

c) The minimum flow rate through the thermal cleaning system shall be monitored by flow control devices

NOTE 1 Further information is given in Annex C

The flow control devices shall be interlocked with the position switches of the dampers that are used to adjust the flow through the thermal cleaning system They shall be designed in such a way that any possible position

of the dampers ensures a minimum volume flow that is required to maintain safe functioning of the thermal cleaning system Manually adjustable dampers shall be fixed after commissioning

d) If variable speed fans are used to adjust the flow through the thermal cleaning system, the control of the fan speed shall be interlocked with the control of the volume flow A minimum flow shall be ensured

NOTE 2 The fan speed can be controlled by a monitoring device e.g by determination of a specified minimum value at the frequency converter The flow can be monitored e.g by means of a differential pressure switch

5.2.2.6 Prevention of insufficient oxidation in systems with recirculation

5.2.2.6.1 General

Thermal cleaning systems with recirculation (see 3.10) of cleaned gases shall be designed in such a way that the inadmissible concentrations according to 5.2.2.2 are avoided In the case of operation faults (e.g incorrect temperature, insufficient flow rate) it shall be ensured that any inadmissible concentration which may occur is not recirculated

NOTE The following parameters have an important influence on a complete oxidation process space temperature, residence time within the process space, mixing within process space, oxygen content

5.2.2.6.2 Additional requirements for catalytic combustion

To avoid ineffective catalytic function the design shall consider ageing, poisoning and/or deposits

To prevent concentrations above the values given in 5.2.2.2 for catalytic combustion systems with recirculation of oxidized process gases, the following measures shall be applied:

a) the type of catalyst shall be selected considering the composition of the process gas, especially the possible occurrence of catalyst poisons;

b) in case of dust loaded process gases effecting the catalytic function, appropriate filters have to be fitted at the inlet of the catalytic combustion system to prevent deposits on the active surface of the catalyst

5.2.2.7 Prevention of adsorption of flammable substances in catalytic combustion systems

Adsorption of flammable substances in catalytic combustion systems shall be avoided by the following measures: a) the minimum temperature of the process gas at the inlet of the catalytic process space shall be defined and monitored The supply of process gas shall be stopped automatically if the temperature falls below the defined minimum

and

b) during heating up of the catalytic system to the temperature necessary for the catalytic reaction, the gas being led through the catalytic process space shall be free of flammable substances Interlocks with the downstream equipment shall be installed to avoid the possibility of adsorption of flammable substances

The experience in designing and operating thermal cleaning systems, as well as experimental and theoretical studies showed that because of the initial degradation of the solvents by partial oxidation during the preheating and the reduced energy release of explosions at increased temperatures these ignition sources do not present a hazard To prevent hazards from explosion, caused by the ignition sources described above, the requirements of5.2.2 shall be observed

NOTE 1 The prevention of hazards from explosion of explosive mixtures of gas, vapour, mist and dust in upstream or downstream equipment and the connecting ductwork, can be ensured by the design and proper selection of electrical and non-electrical equipment to avoid ignition sources in any part of the system, where concentrations above the limits given in 5.2.2.2 a)

or b), respectively, are possible

NOTE 2 Components and the connected ductwork to be considered in this respect are e.g.:

 cleaning machines according to prEN 12921-3;

 ducts for bypassing the thermal cleaning system (emergency bypass);

 ignition sources like e.g.:

 electrical equipment (see EN 60079-0, EN 60529);

 non-electrical equipment (see EN 13463-1, EN 13463-5);

Electrical equipment installed and located in zone 2 shall be at least of category 3 complying with EN 60079-0 and

EN 60079-15

In particular the following measures shall be considered:

 all conductive components shall be interconnected and earthed according to EN 60204-1

5.2.3.3 Non electrical equipment

All non electrical equipment and components installed and located in potentially explosive atmosphere shall be designed and constructed according to good engineering practice and shall be subjected to an ignition hazard assessment in accordance with 5.2 of EN 13463-1:2001 to provide the protection required The equipment shall satisfy the requirements of EN 13463-1 and EN 13463-5

Category 3 equipment for installation in zone 2 shall not contain any effective ignition source in normal operation (see Annex F) Category 2 equipment for installation in zone 1 shall not contain any effective ignition source in normal operation or expected malfunction (see Annex G)

In particular the following requirements shall be observed:

 hot surfaces of all apparatus shall not be able to ignite solvent vapours The admissible temperatures of these

hot surfaces are described in 6.4.2 of EN 1127-1:1997;

 electrostatic charges shall be avoided according 7.4 of EN 13463-1:2001;

 fans shall be designed and constructed according to prEN 14986;

 hoses and pipes for coating materials and for exhausting solvent vapours shall be conductive and electrostatically grounded (resistance less than 108 Ohms)

5.2.4 Protection from explosion effects

If measures following 5.2.2 and 5.2.3 alone or in combination do not deliver a sufficient level of safety, the possible effects of an explosion shall be reduced by one or more of the following measures:

a) explosion-resistant design (see 6.5.2 of EN 1127-1:1997);

NOTE 1 A special EN standard “Explosion proof equipment” is in preparation by CEN/TC 305/WG3

b) explosion relief (see 6.5.3 of EN 1127-1:1997); (Warning: The design of the explosion relief shall not present a new hazard.);

NOTE 2 Explosion venting devices are described in prEN 14797 and dust explosion venting systems are described in prEN

14491

c) explosion suppression (see 6.5.4 of EN 1127-1:1997);

NOTE 3 Explosion suppression systems are described in prEN14373

d) prevention of flame and explosion propagation (see 6.5.5 of EN 1127-1:1997 and EN 12874))

The operating temperatures shall be considered during design and selection of measures

The scope of EN 1127-1:1997 deals with atmospheric conditions, but the general principles are applicable to the conditions in thermal cleaning systems This shall be considered by selecting the protection systems listed above

5.2.5 Measures to avoid overheating and fires

5.2.5.1 Fires caused by condensates and deposits

The design and construction shall prevent condensates and deposits in thermal cleaning systems and/or shall allow safe and easy cleaning Therefore e.g dismountable ducts or a sufficient number of cleaning ports shall be provided Channels and ducts shall be installed as straight as possible

The burning process shall be monitored

The monitoring device shall be interlocked with forced ventilation and the supporting burner gas supply valve

NOTE Further information is given in Annex C

5.2.5.4 Insulation

The heat insulation shall not support a fire or increase the risk of fire

Materials according to Annex E shall be used

Materials for heat insulation shall be at least non easily flammable and shall not loose their properties under operating conditions

Failure of insulation (e.g insufficient thickness, inappropriate material, insufficient protection from external damage)

of heat exchanger(s), ducting, joints, valves and dampers shall be avoided by design and installation

NOTE There are no harmonised standards at this time for non combustible, slow burning, fire resistance properties of materials and national standards will prevail until such time as harmonised standards are available The harmonisation is the responsibility of CEN/TC 114/WG16 Basic information about fire prevention and protection of machines, see EN 13478

5.2.6 Control systems

5.2.6.1 Requirements for safety related parts of control systems

All safety related parts of control systems for the prevention of the occurrence of hazardous explosive mixtures shall fulfil the requirements of category 3 of EN 954-1 The components used shall be designed, constructed, chosen and combined in such a way to withstand the expected operational conditions

The categories of EN 954-1 state the required behaviour of safety-related parts of a control system in respect of its resistance to faults Control systems shall preferably be achieved by the following design of safety related parts or

by any other method that will lead to the required level of protection:

 If the safety related signals are processed only via hardware circuits, a single fault safety with partial fault detection shall be realised, that is that only faults in the auxiliary relays or auxiliary contractors in the control circuits of the safety related functions shall be detected

 If signal processing takes place via a diversity structure, that is via a combination of hardware and computing system, a fault detection is required only in the hardware circuit (auxiliary relays, auxiliary contractors, power contractors)

 When using homogenous hardware redundancy (that is two identical computers) a diversity software is required

 When using different computer hardware (function and monitoring computers) an error of the function computer shall be detected and shall lead to cut-off of the thermal cleaning system; an automatic restart is not permitted

A computer may be e.g a process computer, PLC

NOTE Further information related to PLC, see Bibliography

In case of selecting and combining safety related parts of different categories, 6.3 of EN 954-1:1996 shall be applied

Especially, the safety related parts of control systems shall comply with the requirements mentioned above, resulting from application of:

 injection systems for flammable substances

NOTE An overview of the operating parameters, conditions for use and measurement methods is given in Annex C

5.3 Requirements against hazards generated by residual process gas

It has to be ensured that the hazards of suffocation and intoxication by residual process gas when entering a thermal cleaning system during maintenance or inspection are avoided (see 7.2.3)

6 Verification of the safety requirements and / or protective measures

Table 3 shall be used as a check list for manufacturers to prepare their own specific table of methods used to verify that the safety requirements and measures described in Clause 5 are complied with and contains references to the respective clauses of this European Standard

Table 2 — Methods used to verify the safety requirements and/or measures

Clause measures for thermal cleaning systems Safety requirements and/or protective Inspection a Functional

test b Measuring c Examination of

drawings/ Calculations d5.1 General

5.2 Fire and explosion

5.2.2 Prevention of hazardous explosive mixtures (limitation of concentration of flammable substances)

5.2.2.3 Linking multiple sources to a thermal cleaning

5.2.2.5 Prevention of insufficient forced ventilation × × × × 5.2.2.6 Prevention of insufficient oxidation in systems with recirculation

5.2.2.6.1 General

5.2.2.7 Prevention of adsorption of flammable

5.2.3.1 General

5.2.3.2 Electrical equipment

5.2.3.3 Non electrical equipment

5.2.5 Measures to avoid overheating and fires

b The functional test will show whether the parts in question function in such a way as to satisfy the specific requirements

c Verification by means of measuring instruments is used to check whether the requirements are fulfilled within the specific limits (e.g. the concentrations, purge times, temperatures)

d Drawings and calculations are used to check whether the design characteristics of the components used satisfy the specific requirements