Explosion-proof devices

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. 

Use only explosion-proof devices and nonsparking switches in flammable liquid storage 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. 

The dust-ignition-proof protection concept excludes dust from entering the device enclosure and will not permit arcs, sparks, or heat generated by the device to cause ignition of external suspensions or accumulations of the dust. Enclosure requirements can be found in ANSI/UL 1203-1994, Explosion-Proof and Dust-Ignition-Proof Electrical Equipment for Use in Hazardous Locations. ... 

The surface temperature of explosion-proof enclosures cannot exceed that of high-temperature devices, Equipment can be tested by nationally recognized testing laboratories and given one of 14 T ratings, as indicated in Table 17-2. This equipment may exceed the 80 percent rule."... 

In Division 1 areas, meters, instruments, relays, and similar equipment containing high-temperature or arcing devices must be installed in approved explosion-proof or purged enclosures. Unless such devices are specifically labeled as suitable for Class I, Division 1 areas, it is best to assume they are not suitable. 

Arcing contacts in Division 2 areas must be installed in explosion-proof enclosures, be immersed in oil, be hermetically sealed, or be non-incendive. High-temperature devices must be installed in explosion-proof enclosures. Fuses must be enclosed in explosion-proof enclosures unless the fuses are preceded by an explosion-proof, hermetically sealed, or oil-immersed switch and the fuses are used for overcurrent protection of instrument circuits not subject to overloading in normal use. 

Figure 17-16 depicts typical devices containing arcing contacts enclosed in explosion-proof enclosures. Figure 17-17 shows typical explosion-proof alarm devices. A telephone instrument suitable for Class I, Divisions 1 and 2, Group D classified areas is shown by Figure 17-18. 

Figure 17-17. Standard explosion-proof alarm devices. Courtesy of Crouse-Hinds Electrical Construction Materials, a division of Cooper Industries, Inc.)...

Seals are required at entries by conduit or cable to explosion-proof enclosures containing arcing or high-temperature devices in Division 1 and Division 2 locations. It is not required to seal IM in. or smaller conduits into explosion-proof enclosures in Division 1 areas housing switches, circuit breakers, fuses, relays, etc., if their current-interrupting contacts are hermetically sealed or under oil (having a 2-in. minimum immersion for power contacts and 1-in. for control contacts). 

Except for conduit or cable entries into explosion-proof enclosures containing arcing or high-temperature devices (as described in Item I above), cables that will leak gas through the core at a rate of less than 0.007 ft /hr at 6 in. of water pressure need not be sealed if they are provided with a continuous gas/vapor-tight sheath. Cables with such a sheath that will transmit gas at or above this rate must be sealed if connected to process equipment that may cause a pressure of 6 in. of water at the cable end. 

These devices are tested only for internal explosions and not for external explosions pressurizing the devices from the outside. As an example, a factory-sealed push-button start/stop station connected to an explosion-proof motor starter cannot suffice as a seal for the motor starter conduit entry. A separate seal must be installed at the point of conduit entry. 

If the pumps are located indoors, a Division 1 classification is likely to apply. Motors must be Class 1, group D, explosion-proof, or they may be separately ventilated with clean outside air brought to the motor by fans. Auxiliary devices such as alarm contacts on the motor must be suitable for the area classification. The installed costs, overall efficiencies, and service factors associated with the enclosures that are available will influence the selection. 

Specifically note that Type 7 (explosion-proof) enclosures and their associated conduit systems are neither gas or liquid tight. Consequently, corrosive gases such as hydrogen sulfide and water from rain or internal condensation can accumulate with the enclosure. Premature failure of electrical devices and interconnections often results when preventive measures such as drains, air purges, and dual rated enclosures are not used to remove or exclude these corrosive elements. Type 7 enclosures are intended for indoor use. 

Herbert Bohm et al, Ger(East)P 47317 (1966) CA 65, 16785(1966) [A portable, spark-proof device is described which handles the charging of short boreholes with free-running explosive, such as consisting of 30 parts AN, mechanically mixed with 6ps Diesel oil contg 1% Marvelan (which served as an... 

Fire and Explosion Prevemloa—study areas have included fa) ignition, thl flame propagation. fire detection and alarm, (d) suppression and extinguishing, and (e) methanometry. Devices and techniques tested have included explosion-proof bulkheads, coal dust and rock dust analyzers, ignition suppression devices for face equipment, and remote sealing techniques. 

CAUTION The Goldfisch lipid extraction unit should be operated inside an explosion-proof fume hood to exhaust the vapors from flammable solvents used during normal operation. The fume hood should be equipped with a fire suppression device. 

It is therefore more cost effective to use a large ultrasonic system supplying 80 kW to process liquids at a flow-rate of 10 m /h than to use 5 ultrasonic processors with a power of 16 kW each or 40 processors with a power of 2 kW each. The robustness of the transducer enables its use under heavy-duty industrial conditions. Also, the processor can be designed to be explosion-proof. Like the transducer and the flow cell, the generator is housed in two connected compact stainless steel cabinets. This makes the device self-contained, robust and easy to install. The standard footprint of a 16-kW system is just 600 mm x 1200 mm. 

Flammable or explosive volatiles may be driven out by cavitation and ignition. Virtually no sonication devices are explosion-proof and only extreme measures can render them explosion resistant. 

Butane, isobutane, and propane are asphyxiants and should be handled in a well-ventilated environment it is recommended that environmental oxygen levels are monitored and not permitted to fall below a concentration of 18% v/v. These vapors do not support life therefore when cleaning large tanks, adequate provisions for oxygen supply must be provided for personnel cleaning the tanks. Butane is highly flammable and explosive and must only be handled in an explosion-proof room that is equipped with adequate safety warning devices and explosion-proof equipment. 

ET Obviously some circuitry, electronic and electrical components are not amenable to those power limits, such as pumps and other devices which require p more power. These units have to either have explosion proof or pressurized... 

Figure 3.3 shows various elements required to assemble a load line to a silo. The railearcan also be unloaded by a simpler, manual device (Figure 3.4). This unit can be used for Airslide railcars. The frame serves as a conveying airflow line. It should be noted that an explosion proof design is required for filler unloading.

Check electrical equipment regularly for sparks or arcing. These conditions can trigger spontaneous combustion of flammable gases or cause dust explosions. To prevent electrical equipment from contributing to fires (1) Conduct regular inspections of insulation resistance and monitor the quality of insulation layers. (2) Inspect and correct naked wires and metal contacts to prevent short circuit. (3) Install explosion-proof seals or isolated lighting fixtures, switches and protective devices. 

Any process heat plant design implies piping through the containment to connect the reactor vessel with the chemical plant. The fracture of a pipe could result in the accumulation of a flammable gas mixture in the containment. Precautions must be taken to minimize the risk of a fire or gas explosion such as avoidance of explosive gas ingress, proper detection devices, inerting, sufficient safety distances, appropriate layout of secondary coolant boundary, explosion-proofed wall, plant isolation valve. For the PNP-500, the use of two concentric pipes for the process gas carrying lines were recommended. Alternatives are concrete channels around the gas lines or inerting of the containment [10]. 

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