Explosions Extraction systems

These include, for example, smoke extraction systems. In ventilation and air conditioning systems certain equipment can also require special safety measures (e.g., due to explosion risks). 

The materials of construction, from the cupboard to the fan, should be inorganic and resistant to attack by perchloric acid. For the cupboard itself suitable materials include stainless steel of types, 316 or 317, solid epoxy resin, and rigid PVC. Stainless steel has been popular for this application as it is easy to form, weld, and polish. It is, however, attacked by the acid, which causes discoloration of the metal surface and the formation of iron(III) perchlorate, which can be explosive. Ductwork, separate from other extract systems, is usually made from stainless steel or plastic materials. Fire regulations may preclude the use of plastic ductwork or require it to be sheathed in an outer casing of metal or GRP. The fan casing and impeller can both be made of plastic. 

Several points need to be considered when applying this pressure method of sample collection. All of the extraction system parts must be explosion proof and the distance from the ceramic cup to the sample bottle must be as short as possible. The sample collection bottle should be at the same level as the ceramic cup. If it is higher, additional vacuum will need to be applied to move the sample water into the sample bottle. Sample storage, once the water is collected, is determined by the analyte of interest. 

Smith, M., G. E. Collins, and J. Wang. Microscale solid-phase extraction system for explosives. J. Chromatogr., A 991, 159-167 (2003). 

NEPCCO SoilPurge soil vapor extraction systems are noncontacting, oil-free, explosion-proof vacuum systems designed to remove volatile organic compounds (VOCs) from soil in situ. According to the vendor, benzene, toluene, ethylbenzene, and xylenes (BTEX), chlorinated solvents and other hydrocarbons can be treated with SoilPurge systems. The technology can also remove radon from soil. 

The concentration of particles inside the pipeline is extremely high and beyond the upper explosible limit (UEL). This forms a natural buffer zone or barrier for any explosion that may occur in a vessel at either end of the pipeline (i.e. flame propagation is unlikely). This could avoid the need for explosion suppression and/or isolation, which would be required normally for a dilute-phase or dust extraction system. 

Caution. Selenourea is toxic and should be handled with care. Experiments with selenourea should be conducted in an efficient fume hood or in a glove box vented to a fume-extraction system. The explosive hazard of perchlorate salts of metal complexes should also be noted. 

Dust is a hazard it tends to be generated by dry materials at all open transfer points, which must usually be safeguarded either by the provision of dust extraction systems, or by wetting the material. Combustible dust (coke, feed-grain) may be an explosion hazard. 

The upper hemisphere of the steel shell is surrounded by a shielding made of reinforced concrete with a wall thickness of about 2 m. This shielding protects the nuclear part of the plant against any external impact (e. g. gas explosion, military aircraft crash) it also significantly reduces the likelihood that radionuclides will escape to the environment. The interspace between the steel shell and the secondary containment is held at sub-atmospheric pressure, so that any radionuclides penetrating the steel shell via leaks in the event of a loss-of-coolant accident would be transported by the annulus air extraction system to the standby filters and retained here, thus preventing release to the environment. 

The minimum dust concentration for explosion is measured in the vertical tube apparatus and is used to give an indication of the quantities of air to be used in extraction systems for combustible dusts. Since dust concentrations can vary widely with time and location in a plant it is not considered wise to use concentration control as the sole method of protection against dust explosion. 

Any electrical system used as part of the ventilation or extraction systems must meet rigid electrical standards and as in the case of all such equipment be intrinsically safe. As discussed earlier, classifying hazardous or potentially explosive atmospheres is not only a legal requirement under DSEAR but has been widely used to determine the extent of hazardous zones created by flammable concentrations of vapours. 

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. 

The alternative is hexane, which because of the explosion hazard requires a more expensive type of extractor construction. After the extraction the product is dull gray. The continuos sheet is slit to the final width according to customer requirements, searched by fully automatic detectors for any pinholes, wound into rolls of about 1 m diameter (corresponding to a length of 900-1000 m), and packed for shipping. Such a continuous production process is excellently suited for supervision by modern quality assurance systems, such as statistical process control (SPC). Figures 7-9 give a schematic picture of the production process for microporous polyethylene separators. 

In the 1990s, Pawliszyn [3] developed a rapid, simple, and solvent-free extraction technique termed solid-phase microextraction. In this technique, a fused-silica fiber is coated with a polymer that allows for fast mass transfer—both in the adsorption and desorption of analytes. SPME coupled with GC/MS has been used to detect explosive residues in seawater and sediments from Hawaii [33]. Various fibers coated with carbowax/divinylbenzene, polydimethylsiloxane/divinylbenzene, and polyacrylate are used. The SPME devices are simply immersed into the water samples. The sediment samples are first sonicated with acetonitrile, evaporated, and reconstituted in water, and then sampled by SPME. The device is then inserted into the injection port of the GC/MS system and the analytes thermally desorbed from the fiber. Various... 

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