Types of explosion protection

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. ... 

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

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. 

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. 

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

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

In zone 2, the pressurization technique presents the greatest allowable bandwidth in selecting the electrical components to be installed inside an explosion protected enclosure in comparison with other types of explosion protection techniques as stated in IEC 60079-15, EN 50021 or VDE 0165. As a special feature, pressurization enables intervention and access of personnel... 

To clarify things neither type tests and verifications nor routine tests are the point of this chapter, but inspection and maintenance procedures after installation and before or during service. These procedures shall be done -and this is a general rule - by qualified personnel, who are experienced in the various types of explosion protection, installation practices and rules and the principles of area classification. 

Part two - as the main part of the book - starts with Chapter 6. Here, detailed descriptions of the different types of explosion protection are given, combined with illustrations of today s explosion protected apparatus. Chapter 7 deals with modem contents of pressurization. According to those,... 

Regardless of what type of explosion protection measure is considered, the dust cloud explosion should be prevented from propagating from the location where it originates to other locations in the plant. This is referred to as explosion isolation. Dust explosions can propagate through pipes, chutes, conveyors, etc. The first step in isolating an explosion is to avoid unnecessary connections. If this is not possible, barriers should be created in the path of the explosion. 

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. 

The Hazardous Element. To often it is automatically assumed that in an explosive facility the explosive item is the most hazardous item and, therefore, the electrical protection is designed based on its requirements. However, this assumption can lead to installing the wrong type of electrical protection. 

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 ... 

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. 

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. 

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 ... 

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. 

An explosion is defined in the National Fire Protection Association (NFPA) Fire Protection Handbook as a rapid release of high-pressure gas into the environment. This release of high-pressure gas occurs regardless of the type of explosion that has produced it. The high-pressure energy is dissipated by a shock wave that radiates from the blast center. This shock wave creates an overpressure in the surrounding area that can affect personnel, equipment, and structures (see Figure 3.2). An overpressure of just 0.5 to 1 psi can break windows and knock down personnel. At 5 psi, eardrums can rupture and wooden utility poles can be snapped in two. Ninety-nine percent of people exposed to overpressures of 65 psi or more would die. 

A type of ignition protection where equipment parts which may ignite an explosible atmosphere are enclosed in a casing. This casing is designed to withstand the pressure caused by an explosion of an explosible mixture in its interior. 

To prevent the second type of explosion, make sure batteries have the same voltage before connecting them. Connect negative terminals to a ground last (for cars that have a negative ground) and disconnect them first. Also, one should wear protective eyewear during this operation. 

The mass of the tested explosive charge depends upon the size of the coils and the type of its protection from the blast damage. Thus, for instance, wfren the diameter of the coils is 500 mm, and 10 mm thick nonmagnetic stainless steel casing is used for protection of the coil assembly, then up to 200 g of explosive can be detonated. 

IS circuits IS in instmmentation and controls for hazardous areas is very important and a common means of explosion protection. Distribution of use of IS circuits among various types of instrumentation items is depicted in Fig. X/3.7-l based on data from... 

There are a variety of types of lightning protection systems available and will be selected upon the level of risk. Structures with inherent explosive risks, e.g. explosives factories, fuel stores, dumps and tanks, invariably need the highest possible class of lightning protection system. Details of the requirements can be found in BS 6651 Code of practice for protection of structures against lightning. 

Some types of explosives and tracer or igniter compositions give off toxic fumes when burned Proper protective respiratory equipment, such as hose masks, airline masks, and self-contained breathing apparatus shall be worn where such fumes are likely to be encountered. 

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