Methods of Protection in Hazardous (Explosion Risk) Locations: Containment, Segregation and Prevention

In order to reduce the risk of explosion, elimination of one or more of the components of the ignition triangle is necessary. There are three basic methods of protection—explosion containment, segregation and prevention.
• Explosion containment: The only method that allows the explosion to occur but confines it to a well-defined area, thus avoiding the propagation to the surrounding atmosphere. Explosion-proof enclosures are based on this method.
• Segregation: A method that attempts to physically separate or isolate the electrical parts or hot surfaces from the explosive mixture. This method includes various techniques, such as pressurization, encapsulation, etc.
• Prevention: A method that limits the energy, both electrical and thermal, to safe levels under both normal operation and fault conditions. Intrinsic safety is the most representative technique of this method.
For each method, one or more specific techniques are present that translate into practice the basic philosophy that at least two independent faults must occur in the same place and at the same time in order to ignite an explosion. A fault in a circuit or system that subsequently leads to a failure of another circuit or system is considered a single fault. Naturally, there are limits in considering faults or certain events. For example, the consequences of an earthquake or other catastrophic action may not be considered, because damage caused by the malfunctioning of the protection system during these particular events become insignificant when compared to the damage generated by the main cause.
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  1. I need your help on following issue, although it is not related to this post but I am not sure where to ask new questions.
    I have to install flow computer on natural gas skid, which has been classified as C1D2, Groups C and D area. Flow computer is FM and CSA certified non-incendive for C1D2, Groups A, B, C and d area.
    I need to install a GPRS modem and connect it to flow computer. This GPRS modem is not suitable for installation in hazardous area.
    Also, I have to install a battery charger, rechargeable battery for providing 12 or 24 VDC power to flow computer.
    Flow computer is non-incendive but end user says that they will use IS techniques for installation of equipment in hazardous area.
    I am thinking of installing battery charger, rechargeable battery and GPRS modem in weatherproof enclosure in ordinary location in outdoor location. An IS power supply will be installed at supply power output from this enclosure. The flow computer’s maximum current will be 250 mA at 12 VDC or 125 mA at 24 VDC. My flow computer can accept 12 or 24 VDC power supply, so I can use any one of above.
    I understand that after a certain distance from C1D2 location, the area becomes non-hazardous. I would like to know that what is distance from C1D2 to location, where it becomes non-hazardous (ordinary location) in open atmosphere. If, I know the distance then I can locate my power system and GPRS modem at that distance.
    Kindly help to advise on above.
    Also advise, if you can supply Extrinsically safe or explosion proof junction boxes and enclosures for installation in hazardous area and advise your company email address for sending inquiries for these items.
    Thanks in advance for your assistance.

    1. This needs to be desgned and detailed knowledge of HAC shall be followed

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