Explosion protection defined

In general the fire and explosion protection engineering design philosophy for oil, gas and related facilities can be defined by the following objectives (listed in order of decreasing importance) ... 

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... 

Following the historical development of electrical engineering and explosion protection, zone classification was the objective of national standards and installation rules. Most of the leading industrial countries established an installation practice for chemical plants and the oil and gas industry with two or three zones for areas hazardous due to gas- or vapour-air mixtures and two zones for areas with hazardous dust-air mixtures. Apart from this philosophy, the coal mining industry in most countries tends to avoid an area classification and defines only one category of explosion protection ( firedamp-proof ). More recent standards or directives present a three-zone concept for areas endangered by combustible gas- (vapour-, mist-) air mixtures and dust-air mixtures in industrial plants (other than coal mines). 

Similar to installation rules, national standards for explosion protection in the presence of combustible dusts were established long before international standards. In Germany, VDE 0165/1991-092 (and this standard referring in parts to VDE 0170/0171 Teil 13/1986-11) defines requirements for electrical equipment operating in areas hazardous due to combustible dusts. 

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 ... 

TGL Technische Gute- und Lieferbedingungen, Technical Regulations for Quality and Delivery) have defined the classification of hazardous areas (TGL 30042) and the requirements for construction and testing of explosion protected electrical equipment (mainly TGL 19491). 

Thus, based on the knowledge of the gases occurred and specified zones, each apparatus can be defined completely (as far as explosion protection is concerned), e.g. Ex II2G EEx ib IIC T4, obviously designed for zone 1 application. 

After installation of an explosion protected apparatus and before it is brought into service, it shall be given an initial inspection. During service, regular periodic inspections or continuous supervision shall guarantee the safe operation of the apparatus or system. If necessary, maintenance or repair shall be carried out. The standards define different grades of inspection ... 

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. 

Besides other more or less general obligations, i. e. taking necessary, preferred technical measures and providing supervision to protect the safety and health of workers, the employer has to draw up an explosion protection document. This obligation is independent of the number of employees, firstly, it contains information on the risks that have been determined and assessed and what measures have been taken. Secondly, it requires the classification of places having an explosion risk into zones. In annex 1, explosive zones are defined (see Table 6.3). 

With the introduction of safety standards lEC 61508 and 61511 (for process industries), there is a defined need for proper implementation of safety systems embedded into the main system. The safety life cycle has various phases. Phases 1 and 2 have been discussed at length in previous chapters (Chapter VI and Chapter VII and to a certain extent in Chapter IX). In this part, detailed discussions have been presented to include Phases 3—7, that is, from safety-related systems (SRSs) to modifications. This has been done purposefully so that prior to looking at the detailed implementation part of the standard, readers need to have some knowledge of the safety instrumented system (SIS), safety integrity level (SIL), and their implementation in various instrumentation components. So, this part of the discussions in conjunction with previous chapters will complete the topic of lEC 61508/61511. Safety instrumentation cannot be complete without discussions on explosion protection. With reference to lEC 60079-(0,10,14,15,17, etc.) and NEC (497,499,70, etc.), electrical area, classification of plant, explosion protection, etc. also have been included as part of this chapter to make the system complete in all respects. In view of this, these are presented in two sections. Section 1 for lEC implementation and Section 2 for explosion protection. 

Then, the requirements on manufacturers and operating companies of explosion-protected equipment as specified in the Directives 94/9/EC [1] and 99/92/EC [2] are defined. 

The European directives for explosion protection, Directives 99/92/EC [2] and 94/9/EC [1], define measures for the protection against explosions of explosive atmospheres under atmospheric conditions. The two directives define an explosive atmosphere, as previously mentioned, as a mixture of air and combustible gases, vapours, mists or dusts under atmospheric conditions in which, after an ignition, combustion processes propagate to the complete unburned mixture. However, the two directives do not define atmospheric conditions . 

Therefore, to define the atmospheric conditions the German regulations of the Berufsgenossenschaftlichen Explosionsschutz-Regeln BGR 104 (Explosion Protection Regulations of the Employer s Liability Insurance Association) [5] and the scope of application of the European Standard EN 13463-1 2001 [6] for non-electric apparatus are consulted. 

At the beginning of operation a defined operating pressure at low vacuum is set to evacuate the entire machine using a vacuum pump. To ensure a safe operation of the plant without inertisation, the system has to be operated at a pressure below the minimum ignition pressure of the corresponding organic solvent to fulfil explosion protection demands (Table 13.1) [2]. 

Define plant areas handling hazardous and lethal materials and set rules for design considerations, such as ventilation, explosion walls, etc. Flammable storage materials may require enclosed dikes, foam systems and the like. Refer to National Board of Fire Underwriters or specific insurance company to coordinate recommended protection. Attaway has details on many points to consider. 

The first step in protection against explosions is to identify if they have the possibility of occurring at the facility and to acknowledge that fact. This may be for both internal and open air explosions. Once it is confirmed an estimate of their probability and severity should be defined by a risk analysis. If the risk level is indicated as unacceptable additional measures for prevention and mitigation should be implemented. 

From a fire protection view, all proposed or existing outdoor storage areas should be reviewed, assessed and controlled as to type and quantity of material stored and that the storage area boundaries are well defined. The review and assessment should consider the fire or explosion hazards that the outdoor storage presents to nearby operations or that may be presented by those operations to the storage area itself. 

First, we need to define generally what we are talking about A pressure relief device is any device that can purge a system from an overpressure condition. More particularly, an SRV is a pressure relief device that is self-actuated, and whose primary purpose is the protection of life and equipment. Through a controlled discharge of a required (rated) amount of fluid at a predetermined pressure, an SRV must prevent overpressure in pressurized vessels and systems, and it operates within limits which are determined by international codes. An SRV is often the final control device in the prevention of accidents or explosions caused by overpressure... 

The public access exclusion distance (PAED) provides protection analogous to the inhabited-building distance for explosives. The hazard PAED zone calculated from the MCE shall represent that arc from the agent source containing no more than 10.0, 4.3, and 150,0 mg-min/m of GB, VX, or HD, respectively. Positive means shall be taken to assure that no persons, not directly associated with chemical weapons operations, enter areas so defined. 

The choice of the zero point is an essential element in the safety file of a nuclear test. However, this file covers many other aspects. It specifies the conditions for performing the test in conformity with the defined principles, in order to avoid accidents and ensure the radiological protection of the personnel and the environment. It must satisfy both the severe criteria for defining the explosion point and the many rules governing operational implementation. After examination and approval, this file becomes the reference document for the test in terms of safety. Any subsequent change necessitates a new examination. 

There are several area classification standards such as API RP 500 (2012), API RP 505 (1997), NFPA (National Fire Protection Association) publication 70 (2013), NFPA publication 497, NFPA 70, and local standards in practice. They define classified areas surrounding the individual equipment, based on characteristics and probability of leaked/released liq-uid/gas/solids. This approach reduces fire/explosion risk due to the simultaneous occurrence of a flammable atmosphere and eleetrical ignition to an acceptable level. The project team can use an appropriate area classification standard acceptable to the company and local government authorities. 

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