Design explosion-proof areas

The explosion-proof enclosure is designed such that an explosion in the interior of the enclosure containing the electronic circuits will be contained. The enclosure will not allow sufficient flame to escape to the exterior to cause an ignition. Also, a surface temperature rating is given to the device. This rating must indicate a lower surface temperature than the ignition temperature of the gas in the hazardous area. 

Stores and work areas should be designated No Smoking areas and access controlled. Depending upon scale, explosion-proof electrics and static elimination may be required. 

Stores should be specially designed, constructed of non-combustible material, and located away from other hazards (e.g. brick coal bunkers are suitable for small samples, but purpose-built constructions with explosion-proof lights etc. are required for larger quantities). They should be designated No Smoking areas and be well labelled. 

Process areas are divided into two major types of environments XP and non-XP. XP, for explosion proof, means flammable materials (particularly vapors) might be present at certain times. Non-XP means that flammable materials are not present, even under abnormal conditions. For non-XP designated areas open flames, heated elements, and other sources of ignition may be present. 

Light fixtures should be washable and allow for easy maintenance. Frames are often sealed at the ceiling surface to prevent moisture intrusion and microbiologic growth. Lighting levels in the process areas should be specified in the design. Switches in the hallway or automatic switches facilitate cleaning operations and eliminate the need for expensive explosion-proof devices. 

All equipment designated for use with flammable substances or chemicals or in areas where flammable materials are used, shall be equipped with explosion-proof electrical parts and should be property grounded. 

Design for Hazardous Areas. This type of area classification tends to simplify the electrical design by directive means, but poses alternate choice problems, dictated by economics. The cost of an explosion-proof installation is as much as twice that using standard equipment. As an example of more costly electrical equipment, rigid metal conduit with threaded explosion-proof boxes and fittings are required for all Class I, Division 1, hazardous locations either rigid metal conduit or electrical metal tubing is approved for both Class I and II, Division 2, locations. 

The safe design of components is one of the prerequisites for a safe plant. It is the task of experts of the area in question. For example, explosion proof motors are designed and built by electrical engineers. The great variety of technical components and their safe design, which is component-specific, are not discussed here. The concern rather is the safe design of plants and processes. This refers to the following areas [6] ... 

Store and use dichlorosilane only in adequately ventilated areas. It should be used only in a closed system constructed with compatible materials and designed to withstand the pressures involved. Keep away from heat and all ignition sources such as flames and sparks since dichlorosilane will form flammable mixtures with air and other oxidizing agents. All lines, connections, equipment, and so forth, must be thoroughly checked for leaks and grounded prior to use. Use only spark-proof tools and explosion-proof equipment. 

Explosion-proof vacuum cleaners are specifically designed for use in areas where the presence of flammable gases, vapors or finely pulverized dust in the atmosphere are sufficient to create a threat of explosion or fire. The design of the vacuum must be legally certified and evaluated for hazardous locations by a Nationally Recognized Testing Lab (NRTL) approved by OSHA. Although many vacuum companies claim to offer explosion proof vacuums, it is imperative that you ask for proof of NRTL certification. 

Areas or equipment potentially subject to explosion (including the dust collection extraction system) should also be designed to vent explosive pressure in a safe manner, or be provided with proper suppression, explosion prevention systems, or an oxygen-deficient atmosphere. Also, explosion-proof vacuum cleaners may be fitted with rupture discs. 

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