Gases and vapours classification

Transcription

1 World standards Electrical materials for use in potentially explosive atmospheres must conform to two major certification standards: IEC/CENELEC and NEC The IEC (International Electrotechnical Commission) standards are accepted in practically all countries.they are identical to the European CENELEC standards. The NEC (National Electrical Code) is mandatory in the United States.The 1996 version, art. 505, takes up the IEC designations for gas,temperature classes for materials and zone definition. Gases and vapours classification Gases are divided into four groups in the NEC (National Electrical Code) and three groups for IEC/CENELEC. The groups display the same hierarchy of classification of gases and vapour. Gases and vapours classification Gas or N.American IEC vapour group llc Acetylene A llc Hydrogen B llb Ethylene C llb Ethyl ether C llb Cyclopropane C llb Butadiene C lla Propane D lla Ethane D lla Butane D lla Benzene D lla Pentane D lla Heptane D lla Acetone D lla Ethyl Methyl D lla Methyl alcohol D lla Ethyl alcohol D Temperature classification The IEC and the NEC have also defined a temperature classification for material used in zones at risk of explosion. Temperature classification Temp IEC In ºC N.American T1 450 T1 T2 300 T2 T2 280 T2A T2 260 T2B T2 230 T2C T2 215 T2D T3 200 T3 T3 180 T3A T3 165 T3B T3 160 T3C T4 135 T4 T4 120 T4A T5 100 T5 T6 85 T6 8

2 The New European Directives There are two separate directives relating to potentially explosive atmospheres (ATEX): The first, directive 94/9/EC, deals with the free movement of equipment. It defines the essential safety and health requirements to which equipment and protective systems for potentially explosive atmospheres must conform and the means to monitor their compliance with the relevant standards.this directive also takes into account a complementary directive dealing with the dangers of explosion in relation to the use and installation of equipment. The second and more recent directive, 199/92/EC, deals with employee protection. It defines the minimum requirements for the health and safety of workers likely to be exposed to the risk of explosible atmospheres. It builds on the directive 89/391/EEC which deals with measures to improve health and safety in the workplace. This new directive requires the employer to evaluate the risk of explosion,taking into account the probability of encountering atmospheres,the likelihood of an ignition source arising, the substances used, processes and subsequent interactions, the installation of equipment and the extent of foreseeable consequences.the risk of explosion has to be assessed globally. If a risk exists,the employer must take technical and organisational measures to: prevent the formation of atmospheres, or if that is not possible prevent ignition,or if that is impossible reduce the effects of explosion so that workers do not run any risk. To do this the employer must make an assessment of the risk of explosion, guarantee safety, classify sites where there is a risk of explosion, install equipment appropriate to the site, produce and maintain up-to-date monitoring of explosion risks, taking into account all the above points. Annex 1 of this directive (1999/92/EC) deals with the classification of sites with a dangerous risk of explosion and provides the following definitions: FOR GASES AND VAPOURS or mist is not likely to arise during Zone 22 normal operation,or if it does arise Site where a dangerous atmosphere Zone 0 nonetheless,is of short duration only. consisting of a cloud of combustible dust Site where an atmosphere consisting is not likely to arise during normal of a mixture of air and inflammable FOR COMBUSTIBLE DUST operation,or if it does arise nonetheless, substances in the form of gas,vapour is of short duration only. or mist is present permanently,for long Zone 20 periods or frequently. Site where a dangerous atmosphere Equipment and protection systems consisting of a cloud of combustible must conform to the requirements Zone 1 dust is likely to be present in the air of directive 94/9/EC and be of: Site where an atmosphere consisting permanently,for long periods category 1 for zones 0 and 20 of a mixture of air and inflammable or frequently. category 2 for zones 1 and 21 substances in the form of gas,vapour category 3 for zones 2 and 22 or mist is likely to arise occasionally Zone 21 (see table on page 11) during normal operation. Site where a dangerous atmosphere consisting of a cloud of combustible From 1st July 2003,only products which Zone 2 dust is likely to arise occasionally satisfy the requirements of this directive can Site where an atmosphere consisting during normal operation. be sold commercially and put into service. of a mixture of air and inflammable The regulations are not retrospective substances in the form of gas, vapour for equipment which has already been installed. 9

3 Directive 94/9/EC in practice The major elements of this directive can be summarised as follows: applies equally to electrical and non-electrical products; defines workers health and safety requirements; takes into consideration all potential dangers from equipment; one directive for mines and surface operations; defines the evaluation process for achieving the EC mark of conformity. Areas excluded from the directive The following are notable exceptions from the scope of the directive equipment and protective systems where the explosion hazard results exclusively from the presence of explosive substances or unstable chemical substances; personal protection equipment covered by directive 89/686 EEC; Seagoing vessels and mobile offshore units; Transportation machinery, except vehicles intended for use in explosible atmospheres. The mark This mark is made up from the specific markings of the standards which apply. CE Mark Identification Number of the notified body Surface equipment Category of equipment for Group 2 (existing zones 1 and 21) Gas and vapour Dust Use of material in potentially explosive atmospheres 10

4 Temperature class of product in the presence of combustible dust The following temperature limitation rules must be applied independently of the zone in which it is intended to use the material. The relationship between zone and equipment category for group li Gas and vapour Dust Presence of explosive atmosphere Zone 0: category l Zone 20: category l D Permanent to frequent Zone l: category 2 G Zone 21: category 2 D Occasional Zone 2: category 3 G Zone 22*: category 3 D Irregular and of short duration *only non-conducting dust Equipment for zones at risk of explosion in the presence of combustible dust ZONE 20 ZONE 21 ZONE 22 Dust conducting non-conducting conducting non-conducting conducting non-conducting ingress lp6x lp6x IP6x IP6x IP6x IP5x rating product ll l D ll l D ll 2 D ll 2 D ll 2 D ll 3 D marking Presence of dust cloud The maximum surface temperature of the equipment must not exceed two thirds of the ignition temperature in degrees Celsius of the air-dust mixture concerned. Tmax = 2/3 Tci Where Tci is the ignition temperature of a dust cloud. Presence of layers of dust up to 5mm thick The maximum surface temperature of the equipment must not exceed a value of 75 K less than the minimum ignition temperature of a layer 5mm thick of the dust concerned. Tmax = T5mm-75 K Where T5mm is the ignition temperature of a layer of dust 5mm thick. In a combination of dust cloud and dust layer,take the worst case. 11

5 Criteria for choosing products Classification of gases and vapours Classification of combustible dusts Index of Protection Certified protection concept 1.According to subdivision of gases and vapours This table shows which product classification can be used according to the subdivision of gases or vapours for group ll (surface installations). Subdivision Groups of usable materials gases increased flameproof joint protection vapours safety e d modes d + e A II IIA - IIB - IIC IIA - IIB - IIC B II IIB - IIC IIB - IIC C II IIC IIC Gases or vapours are put into three subdivisions A,B and C according to their experimental safety interstice and their minimum ignition current. 2.According to the ignition temperature of gases The maximum surface temperature of the equipment, indicated by its temperature rating,must always be less than the ignition temperature of the gases. Equipment must never be used in an atmosphere susceptible to catching fire at the temperature indicated by its rating. Ignition Temperature Temperature rating of equipment of gases (ºC) T6 T5 T4 T3 T2 T1 (85 C) (100 C) (135 C) (200 C) (300 C) (450 C) 85 T T <T <T <T <T Material not usable Material usable Classification of equipment in the presence of gases or vapours The table opposite shows by site the gases likely to be present, their subdivisions and the ignition temperature,together with a classification of the materials which are usable. PREMISES SUBJECT TO REGULATIONS (1) SUBDIVISIONS GASES AND VAPOURS (with ignition temperature) Ignition Temperature of gases Subdivision (2) Cleaning products 245 C II or II B Pharmaceutical 90 C II or II C Colourings 385 C II or II A Artificial rubber 300 C II or II C Perfumes 375 C II or II A Spirits 375 C II or IIA Artificial fruit essences 90 C II or II A Artificial textile manufacture 90 C II or II C Paint manufacture 343 C II or II B Varnish manufacture 343 C II or II B Grease solvents 465 C II or II A Resin solvents 343 C II or II A Plastics manufacture 300 C II or II C Hydrocarbons 90 C II or II C Gases used as heat source 300 C II or II C Fertiliser manufacture 500 C II or II C (1) Partial table only (2) For equipment e / for equipment d 12

6 Example In a plastics factory one can find acetone, industrial methane, n-butyl acetate, butanol, ethylene, hydrogen, acetylene. Subdivision of products will be governed by the most explosive gas: hydrogen or acetylene (subdivision C). Electric equipment must be classed ll for protection mode e and llc for protection mode d. The temperature class will be determined by the gas with the lowest ignition temperature here acetylene: 300 C. Electric equipment must be classed T3 minimum (or T4, T5, T6). Classification of combustible dust I According to the conductive properties of the dust It is neccessary to distinguish conductive dust (metallic) from non-conductive dust (non-metallic). Conductive dust has an electrical resistivity equal to or less than 10 3 ohm.m. 2 According to the ignition temperature of the dust The maximum surface temperature of the equipment should always be significantly less than the ignition temperature of the dust and should take account of the presence of dust clouds and/or layers. A B C Acetone Industrial methane Ethyl acetate Methanol Butane Propane Hexane Ammonia Carbon monoxide Pentane Heptane Iso-octane Decane Benzene Xylene Cyclobexane Ethyl/Methyl ketone Methyl acetate N-propyl acetate N-butyl acetate Amyl acetate Butanol Ethyl nitrite Ethylene Butadiene 1.3 Ethylene oxide Hydrogen Carbon sulphide Acetylene Temperature of material rating 465 C 535 C 425 C 385 C 287 C 450 C 223 C 650 C 605 C 260 C 204 C 530 C 205 C 498 C 440 C 245 C 510 C 454 C 450 C 420 C 360 C 363 C 90 C 450 C 420 C 425 C 500 C 90 C 300 C T3 T6 T2 T3 T2 T2 T6 T6 T2 T2 T1 T2 T3 T6 T3 T1 13

7 Classification of gases and vapours Certification standards CENELEC EN and IEC Gases and vapours are classified in three subdivisions according to their experimental safety interstice and their minimum ignition current. Hydrocarbons Alkanes: Butane Cyclobutane Cycloheptane Cyclohexane Cyclopentane Decahydonaphthalene (decaline) Decane Ethane Ethylcyclobutane Ethylcyclohexane Ethylcyclopentane Heptane Hexane Methane Methylcyclobutane Methylcyclohexane Methylcyclopentane Nonane Octane Pentane Propane Olefins: Propene (propelyne) Aromatic Hydrocarbons: Methylstyrene Styrene Benzene hyrdocarbons Benzene Cumene Cymene Ethylbenzene Naphthalene Toluene Trimethylbenzene Xylene Mixed hydrocarbons: Benzol for engines Cleaning solvent or essence Coal naphtha Fuel oil Gas-oil Kerosene Industrial methane Petroleum naphtha (including petroleum essence) Terebenthine SUBDIVISION A Compounds containing oxygen Acids: Acetelic acid Alcohols and phenols: Butanol Cresol Cyclohexanol Diaketone-alcohol Ethanol Heptanol Hexanol Methanol Methycyclohexanol Monanol Octanol Pentanol Phenol Propanol Aldehydes: Acetic aldehyde Metaldehyde Ketones: Acetone Amyl-methyl-ketone Butyl-methyl-ketone Cyclohexanone Ethyl-methyl-ketone 2.4 Pentanedione (acetylacetone) Proplyl-methyl-ketone Esters: Methyl acetate Ethyl acetate Propyte acetate Butyl acetate Omyl acetate Vinyl acetate Methyl acetylacetate Methyl formiate Methyl methacrylate Ethyl methacrylate Oxides (including esters): Dipropylether Carbon monoxide Compounds containing hydrogen Without oxygen: Bromethane Bromobutane Chlorobenzene Chlorobutane Cloroethane Chloroethylene (vinyl chloride) Chloromethane Chloropropane Allyl chloride Benzyle chloridge Methylene chloride Dichlorobenzene Dichloroethane Dichloropropane Benzyl trifluoride With oxygen: Chlorethanol Acetyl chloride Compounds containing sulphur Ethyl-mercapptan Propyl-mercapatan Tetrahydrothiophene Thiophene Compounds containing Nitrogen Acetonitryle Ammonia Nitroethane Nitromethane Amines: Amphetamine Aniline Butylamine Cyclohexylamine Diaminoethane Diethylamine Diethylaminoethanol Dimethylamine Dimethylaniline Methylamine Mono-ethanolamine Propylamine Pyridine Toluidine Triethylamine Trimethylamine 14

8 SUBDIVISION B Hydrocarbons Allylene Butadiene Cyclopropane Ethylene Compounds containing nitrogen Hydrocyanic acid Acrylonitrile Isopropyl nitrate Compounds containing oxygen Acraleine Ethyl acrylate Methyl acrilate Tetrahydofurfurylic alcohol Crolonic aldehyde Dioxalane Dioxane Epoxy-propane Butylic ester of hydroxyacetic acid Butylic ether Ethylic ether Methylic ether Furane Erhylene oxide Tetrahydrofurane Trioxane Mixtures Coke furnace gases Compounds containing halogens Propane,1 chloro,2,3 epoxy (epichorohydrine) Tetrafluoroethylene SUBDIVISION C Acetylene Carbon disulphide Hydrogen 15

9 Substances liable to form a potentially explosive atmosphere Properties of substances liable to form a potentially explosive atmosphere Inflammability limits Ignition Self- by volume % Substances point ignition mixed with air in C temperature in C Lower Upper - flash point (in C), - self-ignition temperature (in C), Inflammability limits Ignition Self- by volume % Substances point ignition mixed with air in C temperature in C Lower Upper - inflammability as volume % in an air mixture. Inflammability limits Ignition Self- by volume % Substances point ignition mixed with air in C temperature in C Lower Upper (*) Ignites with difficulty and only at high temperature (*) Depending on hot material in contact 16