10 degree rule

A 100 Degree Rule was often used in the past throughout the chemical industry to assess whether an accident would occur. According to this rule, if the operating temperature of a process is 100 "C away from the nearest detectable exotherm observed in DSC (Differential Scanning Calorimetry) experiment the operation will not experience this thermal event. In such a case no more detailed information on hazards need be searched for. The 100°C degree rule is, however, often far from the safety margin The use of this rule was the reason of many accidents. 

Hofelich, T. C. and R. C. Thomas, "The Use/Misuse of 100-Degree Rule in the Interpretation of Thermal Hazard Tests," in Proceedings of the International Symposium on Runaway Reactions, Center for Chemical Process Safety/AIChE, New York, NY (1989). 

Often misused rules-of-thumb in the evaluation of thermal hazards are the 100 Degree Rule and similar rules which state that, if the operating temperature of a process is 1(X)°C or some other temperature difference lower than the nearest detectable exotherm observed in a small-scale test, then the process operation will not experience this thermal event and it is not necessary to obtain more detailed information from other, more sensitive tests. Several factors govern the temperature dependent rates of heat generation as detected in small-scale tests. These include the physical aspects of the test procedure such as sample size, the Phi factor, sensitivity and agitation, and the thermokinetic aspects of the reaction being studied, in particular the activation energy. ... 

Hofelich, T.C. and Thomas, R.C., 1989. The use/misuse of the 100 degree rule in the interpretation of thermal hazard tests, Int Symp on Runaway Reactions, 74-85... 

The most universal elimination ordering is given by the Markowitz s rule, reduced to the minimum degree rule in the symmetric case. Let p, and qj denote the numbers of nonzeros in row i and column j of the coefficient matrix A, respectively. Then the Markowitz rule requires us to choose the nonzero entry (Z, j) that minimizes the value iPi — l )iqj - 1) and to move that entry into the pivot position (1, 1) in the first elimination step. (The ties can be broken arbitrarily.) The same rule is applied to the subsystem ofn—k + l remaining (last) equations in elimination step A for = 2, 3,. .., n - 1. In the symmetric case, pi = qt for all i, so the Markowitz rule is reduced to minimization of Pi [rather than of (pi — l)(g - 1)]. For instance, let A be symmetric. 

Hukins et al. (2008) show that, substituting/ = 2 and AT = 10 °C (the 10-degree rule), into equation [8.4], gives an activation energy of 107 /loge2, which if substituted into equation [8.3] yields a value for/that is identical to the predictions of/with the empirical 10-degree rule. 

The predicted life was 580,000h, which was more than 5 times the 100,000h estimated by the empirical ten degree rule This suggested that the results of the hot water immersion test were valid. 

A conical intersection needs at least two nuclear degrees of freedom to form. In a ID system states of different symmetry will cross as Wy = 0 for i j and so when Wu = 0 the surfaces are degenerate. There is, however, no coupling between the states. States of the same symmetry in contrast cannot cross, as both Wij and Wu are nonzero and so the square root in Eq. (68) is always nonzero. This is the basis of the well-known non-crossing rule. 

This is a question of reaction prediction. In fact, this is a deterministic system. If we knew the rules of chemistry completely, and understood chemical reactivity fully, we should be able to answer this question and to predict the outcome of a reaction. Thus, we might use quantum mechanical calculations for exploring the structure and energetics of various transition states in order to find out which reaction pathway is followed. This requires calculations of quite a high degree of sophistication. In addition, modeling the influence of solvents on... 

Polyatomic molecules vibrate in a very complicated way, but, expressed in temis of their normal coordinates, atoms or groups of atoms vibrate sinusoidally in phase, with the same frequency. Each mode of motion functions as an independent hamionic oscillator and, provided certain selection rules are satisfied, contributes a band to the vibrational spectr um. There will be at least as many bands as there are degrees of freedom, but the frequencies of the normal coordinates will dominate the vibrational spectrum for simple molecules. An example is water, which has a pair of infrared absorption maxima centered at about 3780 cm and a single peak at about 1580 cm (nist webbook). 

From the earliest days, the BET model has been subject to a number of criticisms. The model assumes all the adsorption sites on the surface to be energetically identical, but as was indicated in Section 1.5 (p. 18) homogeneous surfaces of this kind are the exception and energetically heterogeneous surfaces are the rule. Experimental evidence—e.g. in curves of the heat of adsorption as a function of the amount adsorbed (cf. Fig. 2.14)—demonstrates that the degree of heterogeneity can be very considerable. Indeed, Brunauer, Emmett and Teller adduced this nonuniformity as the reason for the failure of their equation to reproduce experimental data in the low-pressure region. 

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. 

Resistance to Chemical Environments and Solubility. As a rule, amorphous plastics are susceptible, to various degrees, to cracking by certain chemical environments when the plastic material is placed under stress. The phenomenon is referred to as environmental stress cracking (ESC) and the resistance of the polymer to failure by this mode is known as environmental stress cracking resistance (ESCR). The tendency of a polymer to undergo ESC depends on several factors, the most important of which are appHed stress, temperature, and the concentration of the aggressive species. 

As a general rule, there is an economic break-even point at ca 0.08 mm, which coincides with the defined difference between film and sheet. Film is made mote economically by the bubble method and sheet by the tenter-frame method. The exact thickness for break-even depends on technological improvements, which can be made in both processes, in the degree of control used in regulating them and in quaUty requirements. 

Physical and ionic adsorption may be either monolayer or multilayer (12). Capillary stmctures in which the diameters of the capillaries are small, ie, one to two molecular diameters, exhibit a marked hysteresis effect on desorption. Sorbed surfactant solutes do not necessarily cover ah. of a sohd iaterface and their presence does not preclude adsorption of solvent molecules. The strength of surfactant sorption generally foUows the order cationic > anionic > nonionic. Surfaces to which this rule apphes include metals, glass, plastics, textiles (13), paper, and many minerals. The pH is an important modifying factor in the adsorption of all ionic surfactants but especially for amphoteric surfactants which are least soluble at their isoelectric point. The speed and degree of adsorption are increased by the presence of dissolved inorganic salts in surfactant solutions (14). 

Saccharin imparts a sweetness that is pleasant at the onset but is followed by a lingering, bitter aftertaste. Sensitivity to this bitterness varies from person to person. At high concentration, however, most people can detect the rather unpleasant aftertaste. Saccharin is synergistic with other sweeteners of different chemical classes. For example, saccharin—cyclamate, saccharin—aspartame, saccharin—sucralose, and saccharin—aUtame combinations all exert synergy to various degrees. The blends, as a rule, exhibit less aftertaste than each of the component sweeteners by themselves. 

Although PVT equations of state are based on data for pure fluids, they are frequently appHed to mixtures. 7h.e virial equations are unique in that rigorous expressions are known for the composition dependence of the virial coefficients. Statistical mechanics provide exact mixing rules which show that the nxh. virial coefficient of a mixture is nxh. degree in the mole fractions ... 

---