Dusts definition

Each plant or laboratory should adopt definite rules and procedures for electrical iastahations and work. All iastahations should be ia accordance with the National Electrical Code (NEC) for the type of ha2ard, eg. Class I flammable gas or vapor Class II organic, metallic, or conductive dusts and Class III combustible fibers and the degree of process containment, eg. Division 1 open and Division 2 closed (67). Regardless of the flammabiUty of the materials ia the iastaHed operations, changes ia procedure involving use of such materials often occur, sometimes without concurrent alteration of the electrical iastaHation. 

Definition of Dust E losion A dust explosion is the rapid combustion of a dust cloud. In a confined or nearly confined space, the explosion is characterized by relatively rapid development of pressure with a flame propagation and the evolution of large quantities of heat and reaction products. The required oxygen for this combustion is mostly supphed oy the combustion air. The condition necessaiy for a dust explosion is a simultaneous presence of a dust cloud of proper concentration in air that will support combustion and a suitable ignition source. 

It is important to note that these applications are typical, but not at all definitive. Fabric filters can be used in almost any process where dust is generated and can be collected and ducted to a centralized location. In general, fabric filters come in many different sizes and configurations. In older plants one can find makeshift operations. See Figures 7 and 8 for examples of common configurations and characteristics. 

Threshold lamit Value - The term refers to toxicity by inhalation. The abbreviation used is TLV. The TLV is usually expressed in units of parts per million (ppm) - i.e., the parts of vapor (gas) per million parts of contaminated air by volume at 25 °C (77°F) and atmospheric pressure. For chemicals that form a fine mist or dust, the concentration is given in milligrams per cubic meter (mg/m ). The TLV is defined as the concentration of the chemical in air that can be breathed for five consecutive eight-hour workdays (i.e., 40 hours per week) by most people without suffering adverse health effiects. This is the definition given by the American Conference of Governmental Industrial Hygienists. 

Definition of the terms fume, smoke, dust and grit... 

Smoke is taken as having a particle size of less than one pm. Dust consists of particles I-76 pm in diameter. Grit can be interpreted as particles larger than dust. These definitions were taken from the Beaver Report of November 1954 which formed the basis for the 1956 Act. 

A sample of hops which had been treated with tetraethyl pyrophosphate showed a negative chemical analysis. The plant material was also extracted and the extract added to the drinking water of test animals and sensitive insects. The animals and insects that drank this treated water for several days showed no reaction. With the sensitive insects it would have been possible to detect even a few parts per million. In addition, there have been extensive commercial field applications of the chemical in dust and spray form to crops such as apples, pears, grapes, celery, broccoli, Brussels sprouts, and others up to within a few days of harvest there has been no detectable poison residue on any of the crops. The lack of poison residue with use of tetraethyl pyrophosphate is due to the fact that it hydrolyzes within a few hours of application, breaking down into transient nonresidual and nonpoisonous chemicals. Thus it is possible to use tetraethyl pyrophosphate well up to harvest time of food products without danger of residual poison on crops. The fact that the chemical is used in extremely small amounts is a definite advantage in respect to freedom from poison residue. 

The isotopic distribution of lead (IDMS) in shed teeth from children has been shown to be useful in studies of the history of exposure to lead, including the definition of the source of the exposure, e.g., mine dust vs. food (Gulson and Wilson 1994), so IDMS certainly has important applicability, if not for routine determinations. ICP/MS, however, is easier, more sensitive, allows for multi-element analysis, and provides isotopic data. 

High-pressure structures are capable of withstanding pressures of more than 1.5 psig (0.1 bar gauge). The vent design is based on the definition of a deflagration index for gases or dusts ... 

The Explosives Environment. The Army Materiel Command (AMC), which has the primary responsiblity for manufacture and storage of explosives for the Department of Defense, clarified its definition of the type of hazardous location involved with explosives, propellants, and pyrotechnics in its most recently revised safety manual (4). When the only consideration for hazardous environment is the presence of explosive material, it recommends that the environment be classified as Class II, Group G, with the appropriate division based on the probability of the hazardous element being present in the environment. It further states that consideration must be given to vapors which might be present or to the presence of metallic dust. 

We are all familiar with forces between bodies on a macroscopic scale. If one sits at their desk on earth pondering the view and inadvertently lets go of their lunch sandwich it falls until it lands on your manuscript, your lap or the floor—right Better yet, a cannonball and a softball fall at the same rate. It is the definition of gravity . Long after the Tower of Pisa experiments, we discovered why the moon is in seemingly stable orbit around the earth and the earth around the sun is related to forces between bodies. We are also familiar with electrostatic forces and their effects. Dust from the air in the room is attracted to the screen of everyone s TV because of the electrostatic charge it develops. It would seem reasonable that attraction occurs on a smaller scale and even on a molecular scale that does not involve energies on the order of true chemical bonds. 

Damaging fires are uncontrolled chemical reactions, so fire hazards involving ordinary flammable and combustible materials could be included in the above definition of chemical reactivity hazards. However, this publication seeks to supplement basic fire prevention and protection measures by addressing how to successfully manage other chemical reactivity hazards in the work environment. Consequently, the use of the term "chemical reactivity hazards" in this publication will not include explosion, fire and dust explosibility hazards involving the burning of flammable and combustible materials in air. Storage and use of commercial explosives is also outside the scope of this publication. 

Figure 17-46 shows such a performance curve for the collection of coal fly ash by a pilot-plant venturi scrubber (Raben "Use of Scrubbers for Control of Emissions from Power Boilers, United States-U.S.S.R. Symposium on Control of Fine-Particulate Emissions from Industrial Sources, San Francisco, 1974). The scatter in the data reflects not merely experimental errors but actual variations in the particle-size characteristics of the dust. Because the characteristics of an industrial dust vary with time, the scrubber performance curve necessarily must represent an average material, and the scatter in the data is frequently greater than is shown in Fig. 17-46. For best definition, the curve should cover as wide a range of contacting power as possible. Obtaining the data thus requires pilot-plant equipment with the flexibility to operate over a wide range of conditions. Because scrubber performance is not greatly affected by the size of the unit, it is feasible to conduct the tests with a unit handling no more than 170 m3/h (100 ftVmin) of gas.

Since the scattering due to dust is negligible relative to the very large scattering from colloidal suspensions, procedure (b) is inherently attractive. Using the definition of turbidity t and the interrelation between r and R90, the calibration constant of the instrument is given by... 

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