Explosion protection types

Today loading piers are mostly cathodically protected with impressed current. At moorings for tankers, cathodic protection rectifiers are installed on extinguisher bridges as far as possible from the hazardous area. Otherwise, they must be of an explosion-proof type. 

Section 7.4 presented tlwee major types of explosion. Tliis section more closely examines plant-related explosions, focusing on causes, results, and damage potentials. The means for explosion protection and prevention arc the subject of a subsequent chapter. 

Proper installation is dependent on the existing explosion protection measures and on the corresponding isolation system to be used. This guarantees operability. In addition the application and installation remarks of the manufacturer as well as the limits of application in accordance with the Type-Examination Certificate are to be obeyed in every detail. In Table 23-15 the most frequently used isolation systems for explosion protection measures are summarized. 

Finally, it must be pointed out that all explosion protection devices or systems used in practice may be used only when their pressure rating, flameproof, and functional testing have been proved by competent bodies and their test results including the limits of application are documented in a type test certificate. 

Explosion, Protection in. A review of approved electric switches, motors, meters, recorders and other gear suitable for use in areas where explosives are handled. Being spark proof, they minimize explosion hazards Ref H. Busch, "Die Schutzarten im Explo-sionsschutz (Types of Protection in Explosion Protection), Explosivstoffe 1958, 54—9 (9 refs)... 

Apart from regulations aimed at product quality, there are also issues concerned with the safe operation of certain processes, for example, where genetically modified or pathogenic microorganisms are being handled. In such cases, the bioseparation process is normally contained in other words, the potential for release of hazardous material is minimized by various methods. Many bioseparations also involve the use of solvents which must be handled in appropriately designed equipment and facilities with proper explosion protection. Again there are cost implications associated with these types of processes which must be identified at the outset of the development phase. 

This is the fundamental rule of the primary type of explosion protection the existence of hazardous fuel-air mixtures shall be prevented by an artificial or natural ventilation of plant installations and/or an equivalent tightness of manufacturing equipment. 

The rule described above forms a basis for the secondary type of explosion protection, which results in the avoidance of ignition sources, e.g. by using either a flameproof enclosure of a commutator motor or the pressurized enclosure of a gas analyser, or by limiting the electrical values in intrinsically safe circuits. 

This secondary type of explosion protection will be the main object throughout all the following chapters. It covers burnable substances like gases, vapours, mists as well as dusts, and usually refers to atmospheric air as the second component forming a hazardous atmosphere. Atmospheric conditions are defined as total pressures from 8 104Pa (0.8 bar) to 1.1 105Pa... 

Only in the field of data transmission, communications, remote controlling and monitoring, has the very small energy amount, when switching electric circuits, formed a very useful basis for a special type of explosion protection, the so-called intrinsic safety as given in IEC 60079-11 and EN 50020. 

Due to the quite different structures of industrial plants equipped with electrical installations, there are different probabilities for the existence of potentially explosive atmospheres formed by gas-air, vapour-air or dust-air mixtures. With respect to economical reasons, the types of explosion protection for electrical apparatus and systems will depend strongly on the explosion risk at the installation point. It is very unusual to construct and build all explosion protected electrical apparatus in such a manner that they can operate permanently in a surrounding hazardous atmosphere with combustible gases, vapours and dusts in air. The common way is to classify different areas in industrial plants according to the probability for the existence of a hazardous atmosphere and to establish adequate types of explosion protection. In other words, industrial plants with potentially explosive atmospheres are divided and classified into zones. ... 

This marking system correlates the adequate zone on the explosion protected apparatus with traditional data, e.g. group, type of protection and temperature class (see Chapter 5). 

Until 1999, there exists no international standard for explosion protected electrical apparatus intended for the application in zone 0. Intrinsically safe circuits according to IEG 60079-11 and EN 50020, category ia, seemed to be an appropriate type of protection for zone 0 for some time. In the same way, for coal mines the first international standard describing the requirements for electrical apparatus that are intended for operation in the presence of methane/coal dust-air mixtures was prepared in 2000. 

As an example of dust explosion protected apparatus standard IEC 61241-4, 1st edition 2001-3, types of protection pD describes a pressurization technique the interior of this apparatus is subjected to a continuous pressure from a supply of air (not containing any combustible substances) or other inert gases while electrical components within the enclosure are energized. 

Table 3.1 Types of explosion protection and marking according to VDE 0170/0171/1969-01...

Type of protection Firedamp-proof Explosion protected... 

Special protection comprises all protection techniques such as powder filling, static pressurization and encapsulation (by plastics materials). At that time, these techniques started their career in the field of explosion protection and advanced to autonomous types of protection described by IEC or European Standards individually. VDE 0170/0171/1969-01 does not contain any specific requirements for these techniques. It has been the decision of the certifying body that an s -apparatus will operate at the same level of safety compared with other well-defined types of protection, e.g. flameproof enclosure d ... 

Explosion protected electrical equipment for zone 1 (Group II, category 2 G) and the classical firedamp-proof apparatus for coal mines (Group I, category M2) are covered by the B module (EC-type examination) and by the C module (conformity to type) or the E module (product quality assurance). Alternatively, with respect to the B module, the notified body issues an EC-type examination certificate (in German EG-Baumusterpriifbescheinigung), whose marking mainly includes ... 

Table 3.11 lists the notified bodies according to Directive 94/9/EC. It is noteworthy that competence and responsibility of a notified body may be restricted to certain types of explosion protected equipment (e.g. non-electrical apparatus only), to one group only (e.g. Group II) or to a selection of modules, e.g. to quality assurance related modules. The notified bodies are not obligated to cover the complete field of explosion protection. Nevertheless, some notified bodies cover the total range and can provide a single-stop-procedure to their clients. 

It shall be emphasized that all markings described in this chapter are related to explosion protection only and shall be considered as an additional marking to that given in the standards for non-explosion protected apparatus, e.g. the manufacturer s name or his trademark, type code and rated power/ voltage/current/speed/torque, serial number etc. 

IEC and EN Standards ask for marking the type of protection as an abbreviation completed by the classification scheme (temperature class, explosion group) as described in the previous chapter. Table 5.1 gives a survey of the types of explosion protection and their abbreviations. Table 5.2 summarizes the IEC and EN marking code. 

In the following, some examples for marking of explosion protected apparatus are given (the manufacturing companies are fictitious). It is assumed that these apparatuses have been manufactured, type tested and certified under the old article 100 directives (Table 3.6), applicable until 2003-06-30. 

For explosion protected electrical equipment manufactured, type tested, certified and commissioned under the ATEX 100a Directive, the marking described in Table 5.2 shall be added by the marking code given in Table 5.3. The Ex in a hexagon has been taken from the old article 100 directives, whereas the B, C, D or E marks for the generation of Harmonized Norms have been deleted. 

This chapter will seek to answer the question Why do standards ask for specified temperatures of windings, for limited gap and joint values and for restricted voltages and currents in electric circuits The following intends to clarify the physical background of the standards technical content, to explain the methods of explosion protection in electrical engineering, and demonstrate modem explosion protected apparatus to give an appreciation of the bandwidth of the different types of protection. 

The q-standards restrict the application of this type of explosion protection to electrical apparatus or components with ... 

It should be emphasized that the general requirements in the field of explosion protection, i.e. IEC 60079-0 and EN 50014, ask for constructional details for luminaires independent of their type of protection ... 

The lowest ambient temperature for explosion protected electrical apparatus is normally rated at -20°C or T2 = 253 K. Compared with the type test conditions (see Section 8.1) for reference pressure determination in a laboratory at +20°C or % = 293 K, the explosion pressure is increased by 16% only. 

Following the philosophy of explosion protection, the piping for cooling water shall be considered as empty and, as a part of the environment, filled with the gas-air mixture according to the grouping of the motor. (This is the practice when type testing such a motor for flameproofness.)... 

Transmitters are used to record different physical quantities, e.g. temperature, presssure, flow, level, pH value and so on. The mechanical design corresponds to requirements at the place of duty. Due to the small power demand, type of protection intrinsic safety - i is an obvious choice in the field of explosion protection in most cases. 

The schematic circuit diagram of an intrinsically safe fieldbus according to IEC 61158-2 (physical layer) is given in Fig. 6.212. The field devices are certified as intrinsically safe apparatus. Four-wire transmitters with an external power supply are explosion protected by an additional type of protection,... 

Intrinsic safety combined with other types of explosion protection... 

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