Class division system

Zone systems are followed in area classification by ATEX and lEC, and even NFPA has included zone systems of classification in their standard. The zone classification system probably has the edge over the class/division system because many consider the zone classification system to be more flexible and safer in hazardous locations. However, zone systems do not take care of the consequence of release. In case the consequences are important, as per the advice of the HSE.UK, it is better to go for a more conservative equipment selection. Although not officially accepted yet, various sources have tried to place time limits on these zones. The most commonly used values are as shown in Table X/3.3.2-l based on probability and duration of explosive atmosphere. 

Table XI3.3.4 4 Protection Concepts Class Division System ...

Hazardous (classified) locations have traditionally been designated by Class, Division, and Group. Equipment used in areas so designated is selected and systems are designed, based on requirements established for the classification. This approach is defined in Article 500 of the NEC and API 500. 

Various types of hazardous atmospheres are classified to make it easier to discern the specific equipment needed to work in a given hazardous atmosphere. Most manufacturers use these classifications in their operating specifications. This classification system is clearly laid out in NFPA 497 and should be studied to get an understanding of the system. The most common classifications are Class, Division, Group, and Zone. 

During a total loss of off-site power, the Class IE system is powered automatically from two non-Class IE standby diesel generators. If these are not available, each division of Class IE isolates itself from the non-Class IE system, and power to safety-related loads is provided uninterrupted by the Class IE batteries. The batteries are sized to power safety-related loads for a 72 hour period. 

Division of the receptors in the adrenergic nervous system into two classes (a and P) was proposed in 1948 (39) when a difference in the rank order of potency of epinephrine (1, R = CH ), norephinephrine (1, R = H), and isoproterenol [7683-59-2], C H yNO, (1, R = CH(CH3)2) was noted to depend on the organ examined. Eurther subdivision into groups P2 proposed in 1967 (40). Both types of P-adrenoceptors are found throughout the... 

RP 14F Recommended Practice for Design and Installation of Electrical Systems for Offshore Production Platforms RP. 500 Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified As Class I, Division 1 and Division 2. 

Std. 303 Recommended Practice for Auxiliary Devices for Motors in Class 1, Groups A, B, C, and D, Division 2 Locations RP 446 Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications... 

Certain proteins endow cells with unique capabilities for movement. Cell division, muscle contraction, and cell motility represent some of the ways in which cells execute motion. The contractile and motile proteins underlying these motions share a common property they are filamentous or polymerize to form filaments. Examples include actin and myosin, the filamentous proteins forming the contractile systems of cells, and tubulin, the major component of microtubules (the filaments involved in the mitotic spindle of cell division as well as in flagella and cilia). Another class of proteins involved in movement includes dynein and kinesin, so-called motor proteins that drive the movement of vesicles, granules, and organelles along microtubules serving as established cytoskeletal tracks. ... 

The equipment used in this application included two Waters M-45 pumps, a Waters 481 UV detector with microbore cell, an air-actuated Rheodyne 7413 injection valve with a 1-pl injection loop, an air-actuated Valeo four-port sampling valve (A2CI4UW2) with no groove in the injection entry ports, an air-actuated Valeo three-port switching valve (AC3W), and a Digital Equipment LSI-11/23 microcomputer. The LC system was located in a purged cabinet suitable for use in Class I, division 2 areas. The cabinet was in a heated room about 40 feet from the reactor column. The two Valeo valves were mounted next to the reactor column, while the microcomputer was located in the control room. 

Thus, propanol, C3H70H, has a membership of 1 in the three-carbon molecule class, while ethanol, C2H5OH, has a membership of 0 in the same class. As the membership in a crisp set must take one of only two possible values, Boolean (two-valued) logic can be used to manipulate crisp sets. If all the knowledge that we have can be described by placing objects in sets that are separated by crisp divisions, the sort of rule-based approach to the development of an expert system described in the previous chapter is appropriate. 

Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, II and III, Division 1, Hazardous Locations, UL 913, Underwriters Laboratories, Inc., Northbrook, IL, July 1979 Installation of Intrinsically Safe Instrument Systems in Class I Hazardous Locations, ISA-RP12.6, Instrument Society of America, Research Triangle Park, NC... 

Quantitative models of solute-solvent systems are often divided into two broad classes, depending upon whether the solvent is treated as being composed of discrete molecules or as a continuum. Molecular dynamics and Monte Carlo simulations are examples of the former 8"11 the interaction of a solute molecule with each of hundreds or sometimes even thousands of solvent molecules is explicitly taken into account, over a lengthy series of steps. This clearly puts a considerable demand upon computer resources. The different continuum models,11"16 which have evolved from the work of Bom,17 Bell,18 Kirkwood,19 and Onsager20 in the pre-computer era, view the solvent as a continuous, polarizable isotropic medium in which the solute molecule is contained within a cavity. The division into discrete and continuum models is of course not a rigorous one there are many variants that combine elements of both. For example, the solute molecule might be surrounded by a first solvation shell with the constituents of which it interacts explicitly, while beyond this is the continuum solvent.16... 

The EC system of classification is based on the division of enzymes into six major classes according to the reaction they catalyse (Table 3.1). Each class is subdivided. In class 1, oxidoreductases, this is done according to the nature of the electron donor 1.1 with CHOH group as donor 1.2 with aldehyde or 0x0 group as a donor 1.3 with CH2-CH2 group as donor, etc. A further subdivision is achieved by consideration of the electron acceptor 1.1.1 with NAD as acceptor 1.1.2 with cytochrome as acceptor 1.1.3 with O2 as acceptor, etc. Finally, each enzyme that catalyses a unique reaction is given a fourth number so that, for... 

Aminoglycoside efflux is a significant mechanism of aminoglycoside resistance in bacteria of the genera Pseudomonas, Burkholderia, and Stenotrophomonas. There are five classes of transmembrane efflux systems associated with antibiotic resistance however, the resistance nodulation division (RND) family is the predominant class (Table 3.1). ... 

The general class of triazolopyridines includes five heterocyclic systems. Three have bridgehead nitrogen, compounds 1-3 and two do not, compounds 4 and 5. In general these two major divisions reflect differences in synthesis or in properties. Compounds 4 and 5 can exist in several tautomeric forms there is little direct evidence on the major tautomer, and the compounds are therefore shown throughout in the 1H form. 

FIGURE 26-31 Rous sarcoma vims genome. The src gene encodes a tyrosine-specific protein kinase, one of a class of enzymes known to function in systems that affect cell division, cell-cell interactions, and intercellular communication (Chapter 12). The same gene is found in... 

NFPA 497A [5.12]—All electrical systems within 15 ft of the vehicle (when in the repair bay) should be rated for use in Class 1 Division 2 locations. 

Based on NEC requirements for conventional fuels, all electrical systems both above and within 18 in. below the ventilation systems air inlet should meet NEC s Class 1 Division 2 rating. 

Radioactive wastes that arise from operations of the nuclear fuel cycle are divided into five classes, called spent nuclear fuel, high-level waste, transuranic waste, low-level waste, and uranium or thorium mill tailings. At the present time, NARM wastes are not formally divided into different classes (see Section 4.1.2.4). The division of all radioactive waste into fuel-cycle and NARM waste and the division of fuel-cycle waste into five classes constitutes the basic classification system for radioactive waste in the United States. 

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