Post by account_disabled on Jan 7, 2024 22:36:24 GMT -8
An explosion occurs when a sufficient concentration of flammable substances, such as gases, vapors, or combustion dust, mixes with oxygen in the air. The presence of an ignition source, such as a spark, fire, or heat, can then cause rapid combustion, leading to an explosion. Chemical plants and oil stations are common examples of hazardous areas with explosive atmospheres. These areas are defined as dangerous due to the high risk of fire and explosions resulting from lightning strikes and voltage spikes. It is important to note that safety measures must be taken to reduce the risk of explosions, prevent property damage from lightning and ensure that plants are available. This includes the use of internal safety equipment, an effective floor plan and critical ground protection devices. Classification of dangerous areas The two ATEX directives require manufacturers and employers to comply with the requirements outlined to enhance the health and safety of workers, equipment, and safety systems that are at risk from explosive atmospheres. Areas with explosive atmospheres can be classified into zones based on the frequency and duration of explosive atmospheres. Classification helps in determining the level of protection required (Table 1).
Table 1 - Classification of dangerous areas Table 1 - Classification of dangerous Job Function Email Database areas ATEX directives apply to many industries, including oil and gas, chemical, pharmaceutical and mining. Area classification plays an important role in risk assessment, equipment selection, safety measures and general risk management in areas where explosions may occur (Figure 1). Lightning protection for hazardous areas Comprehensive lightning protection for hazardous areas should be designed with an air termination system, ground and intermeshed balanced connection. The system should meet the requirements set out in IEC 62305. The class of LPS II is determined by using the rotation method for explosive areas. However, in case of a lightning strike to the air termination system, flashover may occur at the strike point. To avoid sparks, air termination systems should be installed outside Ex areas. Metal structures can be natural air-termination systems if reaching the minimum material thickness of 5mm. An isolated LPS is required with adequate separation distance to remove the risk of sparking or explosion of combustible materials. Figure 1 - The basic division of the installation into fire protection Figure 1 – Basic division of an installation into lightning protection zones Earthing & equipotential bonding .
All conductive parts are connected via intermeshed equipotential bonding system to the ground with the intervals of 20 m at ground level. Intermeshed equipotential bonding system involves interconnecting all conductive elements to create a network where they share the same electrical potential. The cross-section of the copper earthing conductor for equipotential bonding must be at least 4 mm2. Earthing helps prevent the buildup of static charges on equipment or surfaces, reducing the likelihood of sparks and that could ignite flammable gases, vapors, mists, or dust in explosive atmospheres. It is advisable to install a separate earth-termination system for every single building or part of an installation. Using corrosion-resistant conductors, bonding methods, and protective coatings is crucial for maintaining long-term integrity in explosive areas. Besides, proper separation distance between the air-termination system or down conductors must be regulated in accordance with requirement of IEC 62305. High-voltage resistant, insulated down conductors could be applied when the separation distance is not easy to be maintained. Figure 2 - An intermeshed earth-termination system Figure 2 – An intermeshed earth-termination system Surge protection for hazardous areas In areas with explosive atmospheres, intrinsically safe (IS) electrical systems and devices are often required. These systems are designed to limit electrical energy to levels below the ignition threshold.
Table 1 - Classification of dangerous areas Table 1 - Classification of dangerous Job Function Email Database areas ATEX directives apply to many industries, including oil and gas, chemical, pharmaceutical and mining. Area classification plays an important role in risk assessment, equipment selection, safety measures and general risk management in areas where explosions may occur (Figure 1). Lightning protection for hazardous areas Comprehensive lightning protection for hazardous areas should be designed with an air termination system, ground and intermeshed balanced connection. The system should meet the requirements set out in IEC 62305. The class of LPS II is determined by using the rotation method for explosive areas. However, in case of a lightning strike to the air termination system, flashover may occur at the strike point. To avoid sparks, air termination systems should be installed outside Ex areas. Metal structures can be natural air-termination systems if reaching the minimum material thickness of 5mm. An isolated LPS is required with adequate separation distance to remove the risk of sparking or explosion of combustible materials. Figure 1 - The basic division of the installation into fire protection Figure 1 – Basic division of an installation into lightning protection zones Earthing & equipotential bonding .
All conductive parts are connected via intermeshed equipotential bonding system to the ground with the intervals of 20 m at ground level. Intermeshed equipotential bonding system involves interconnecting all conductive elements to create a network where they share the same electrical potential. The cross-section of the copper earthing conductor for equipotential bonding must be at least 4 mm2. Earthing helps prevent the buildup of static charges on equipment or surfaces, reducing the likelihood of sparks and that could ignite flammable gases, vapors, mists, or dust in explosive atmospheres. It is advisable to install a separate earth-termination system for every single building or part of an installation. Using corrosion-resistant conductors, bonding methods, and protective coatings is crucial for maintaining long-term integrity in explosive areas. Besides, proper separation distance between the air-termination system or down conductors must be regulated in accordance with requirement of IEC 62305. High-voltage resistant, insulated down conductors could be applied when the separation distance is not easy to be maintained. Figure 2 - An intermeshed earth-termination system Figure 2 – An intermeshed earth-termination system Surge protection for hazardous areas In areas with explosive atmospheres, intrinsically safe (IS) electrical systems and devices are often required. These systems are designed to limit electrical energy to levels below the ignition threshold.