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In many industries, gases, vapours, mist and dust develop and escape in the course of manufacturing, processing, transporting and storing combustible substances. Explosive atmospheres may arise when they come into contact with oxygen, and if ignited, explosions occur that may result in catastrophic damage to human life and property. Industries such as oil and gas, chemicals, petrochemicals, pharmaceuticals, fertilisers, food and beverages, biofuel and waste water are considered potential for explosions in general. Safety regulations to avoid explosions have been developed worldwide in the...

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TABLE OF CONTENTS FOREWORD 1. PHYSICAL PRINCIPLES AND DEFINITIONS 2.1 Explosion protection worldwide 2.2 Explosion protection in the European Union 2.2.1 Installation and operation 2.2.2 Selection of equipment 2.3 Explosion protection in North America 2.3.1 Installation and operation 2.3.2 Selection of equipment 3.1 Zone classification 3.2 Equipment categories and equipment protection level (EPL) 3.3 Equipment groups 3.4 Ignition temperature and temperature classes 3.5 Protection types 3.5.1 Application of protection type intrinsic safety “i” 3.5.2 Application and combination of protection...

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5.1 Safety characteristics of combustible gases and vapours    50 5.2 Enclosure protection types to IEC 60 60529 - IPXX    51 5.3 Enclosure protection types to NEMA standards    51

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1. PHYSICAL PRINCIPLES AND DEFINITIONS Explosion protection is a key area of safety engineering. So it is essential to understand the fundamental principles of an explosion and its causation factors. The first chapter of our brochure familiarises readers with the main principles and terms in the field of explosion protection. Combustible substance An explosion is the sudden chemical reaction of a combustible substance with oxygen, resulting in the release of a high amount of energy. An explosion can only occur when three factors are present at the same time (see Fig. 1): Combustible...

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0 vol% explosion range j    mixture too rich partial combustion, no explosion Explosive limits To form an explosive atmosphere, the combustible substance must be present in a certain concentration (see Fig. 2). In the case of insufficient concentrations (lean mixture) or excessive concentrations (rich mixture) no explosion takes place, but a stationary or non-combustive reaction. It is only in the range between the lower (LEL) and upper (UEL) explosive limits that the mixture reacts explosively when ignited. The explosive limits depend on the ambient pressure and the percentage of oxygen in...

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1. PHYSICAL PRINCIPLES AND DEFINITIONS Minimum ignition energy Secondary explosion protection The supply of a specific amount of energy is required to ignite a potentially explosive atmosphere. Minimum ignition energy is the term applied to the minimum amount of energy, for instance when discharging a capacitor, which is just sufficient to ignite the respective combustible mixture. The minimum ignition energy is in the area of 10-5 joules for hydrogen and up to a few joules for certain dusts. If explosion hazards cannot be entirely or only partially excluded by measures to prevent the...

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The requirements of electrical equipment for explosive atmospheres are multifarious: national and international regulations, directives and standards must be observed and ensure maximum safety. The following chapter summarises the main legal requirements and recommendations worldwide, in the European Union and in North America to provide the reader with an overview.

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2.1 EXPLOSION PROTECTION WORLDWIDE The International Electrotechnical Commission (IEC) is responsible for global standards in the field of electrical engineering. IEC publications regarding the explosion protection of electrical equipment and installations are drafted by the Technical Committee TC31 and are deemed as recommendations. All standards observe the latter as far as possible. Until recent years, regulations for gas explosion hazardous areas were stipulated in the 60079 standard series and those for dust explosion hazardous areas in the 61241 series. As many requirements are...

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Recognised IECEx certification bodies (ExCB = certification body) and IECEx test laboratories (ExTLs) exist worldwide and are accredited on the basis of high standard criteria and regularly monitored. An IECEx certificate is only issued if test sample type testing is successful and an audit verifies that an effective quality management system is in place. However, different regional and national approval procedures currently exist all over the world, including for example the ATEX directive in the European Union or national approvals in the USA (UL, FM). Besides the IECEx Scheme for testing...

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The requirements of protection types for areas with combustible dust were contained in the IEC 61241 series. In Europe these EN 61241 standards replace the former EN 50281 series. However, since most requirements for gas and dust are similar, they are compiled under the series IEC or EN 60079 (see Table 3). Table 4: Non-electrical equipment for use in hazardous areas EN Basic Principles and Requirements Protection by flow restricting enclosure “fr” Protection by flameproof enclosure “d” Protection by constructional safety “c” Protection by control of ignition source “b” Protection by liquid...

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2.2.1 INSTALLATION AND OPERATION Directive 1999/92/EC “Minimum requirements for improving the health and safety protection of workers potentially at risk from explosive atmospheres” explains the principles of the operation of systems in hazardous areas. It is thus directed at operators (employers). They must assess the explosion hazard, classify the system into hazardous zones and document all measures to protect employees in the explosion protection document. Evaluation of explosion risks When assessing explosion risks, the following should be taken into account: • Likelihood and duration...

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