Time factors

This time factor must be estimated for the effective design of safety measures and compared with the Time to Maximum Rate (TMRld), giving the upper limit of the time frame. In fact, by applying Van t Hoff rule, the reaction rate doubles for a temperature increase of 10 K. If a temperature alarm is typically set at 10 K 

The oxidation process takes place once a fresh coal surface is exposed to air however, the oxygen absorption rate is inversely proportional to time if the temperature remains constant. Therefore, if the coal is stockpiled so that the temperature in the pile does not rise appreciably insofar as the heat is removed at least as fast as it is generated by the oxidation process, the oxidation rate and, thus, the deterioration or weathering rate of the coal will lessen with time (Vaughn and Nichols, 1985). 

Even if polymerization reactions are critical from the point of view of thermal process safety, there are means to systematically identify the risks and to design the 

Moritz, Sichere Handhahung chemischer Reaktionen, Dechema, Frankfurt a.M., 1995, Vol. 3, p. 115. 

Barton, P. F. Nolan, Safety of chemical batch reactors and storage tanks, ECSC, EEC, EAEC, Brussels, 1991. 

Guidance for the safe production of phenolic resins, British Plastics Eederation, London, 1979. 

ESCIS (Expert Commission for Safety in the Swiss Chemical Industry), Lucerne, 1993, Vol. 8. 

---

The residue in the flask will contain the sodium (or potassium) salt of the acid together with excess of alkali. Just acidify with dilute sulphuric acid and observe whether a crystalline acid separates if it does, filter, recrystallise and identify (Section 111,85). If no crystaUine solid is obtained, the solution may be just neutralised to phenolphthalein and the solution of the alkali salt used for the preparation of a crystaUine derivative. This wiU confirm, if necessary, the results of hydrolysis by method 1. If the time factor is important, either method 1 or the product of the caustic alkali hydrolysis may be used for the identification of the acid. 

In most applications, a bar primary CT is generally used and a normal CT may be suitable. But for too small ratings, where the use of a wound primary CT is imperative, short-circuit effects must be considered, except the CTs for an LT system, where the fault level for such small ratings may be very low and may not matter (Section 13.4.1(5)). For applications on an HT system, where a wound primary CT is imperative, choice of a CT from standard wound primary CTs may still be possible, meeting the minimum requirements of class of accuracy, VA burden and short-time rating. lEC 60044-1 indicates for measuring and protection CTs the maximum short-time factors (STF) that can be obtained economically for a normal wound primary CT where... 

Table 15.11 Maximum short-time factors obtainable economically corresponding to rated output, accuracy class, accuracy limit factor and rated short-time for wound primary current transformers...

Air quality standard (AQS) A standard providing a level beyond which air pollutants in the atmosphere can cause damage to plants, animals, or materials. The concentration and time factors have to be considered. 

In theory, volatile impurities can easily be removed from the nonvolatile ionic liquid by simple evaporation. However, this process can sometimes take a considerable time. Factors that influence the time required for the removal of all volatiles from an ionic liquid (at a given temperature and pressure) are a) the amount of volatiles, b) their boiling points, c) their interactions with the ionic liquid, d) the viscosity of the ionic liquid, and e) the surface of the ionic liquid. 

The time factor in stepwise potentiostatic or potentiodynamic polarisation experiments is very important, because large differences can be caused by changes in the scanning rate. Since the steady state depends on the particular system and conditions of exposure, no set rule exists for the magnitude or frequency of potential changes. Chatfield etal. have studied the Ni/H2S04 system and have shown how becomes more passive with increase in sweep rate. 

Suppose we offset this motion by applying a Galilean transformation x = x +Pt ). In the new reference frame, the system will move just as it did in the old reference frame but, because a — /pqt = / i P )t/A, its diffusion is slowed down by a Lorentz-Fitzgerald-like time factor 1-/3. Intuitively, as some of the resources of the random walk computer are shifted toward producing coherent macroscopic motion (uniform motion of the center of mass), fewer resources will remain available for the task of producing incoherent motion (diffusion). [tofI89]... 

From a practical review, perhaps it can be stated that buildings and construction materials are exposed to the most severe environments on earth, particularity when the long time factor is included. The environments include such conditions as temperature, ultraviolet, wind, snow, corrosion, hail, wear and tear, etc. Basically the following inherent potentials continue to be realized in different plastics ease of maintenance, light weight, flexibility of component design, combine with other materials, corrosion/abrasion/weather resistance, variety of colors and decorative appearance, multiplicity of form, ease of fabrication by mass production techniques, and total cost advantages (combinations of base materials, manufacture and installation). 

Time, pressure, and temperature controls indicate whether the performance requirements of a molded product are being met. The time factors include the rate of injection, duration of ram pressure, time of cooling, time of piastication, and screw RPM. Pressure requirement factors relate to injection high and low pressure cycles, back pressure on the extruder screw, and pressure loss before the plastic enters the cavity which can be caused by a variety of restrictions in the mold. The temperature control factors are in the mold (cavity and core), barrel, and nozzle, as well as the melt temperature from back pressure, screw speed, frictional heat, and so on in the plasticator. 

The NMR spectra can be used to obtain kinetic information in a completely different manner from that mentioned on page 294. This method, which involves the study of NMR line shapes, depends on the fact that NMR spectra have an inherent time factor If a proton changes its environment less rapidly than 10 times per second, an NMR spectrum shows a separate peak for each position the proton assumes. For example, if the rate of rotation around... 

Compliance with U.S. EPA s design performance standards can be demonstrated through one-dimensional, steady-state flow calculations, instead of field tests. For detection sensitivity, the calculation of flow rates should assume uniform top liner leakage. For detection time, factors such as drain spacing, drainage media, bottom slope, and top and bottom liners should all be considered, and the worst-case leakage scenario calculated. 

Equilibrium thermodynamics was developed about 150 years ago. It is concerned only with the achievement of an equilibrium state, without taking into account the time which a system requires for the transition from an initial to a final state. Thus, only the thermodynamics of irreversible processes can be used to describe processes which lead to the formation of self-organising systems. Here, the time factor, and thus also the rate at which material reactions occur, is taken into account. Evolutionary processes are irreversibly coupled with temporal sequences, so that classical thermodynamics no longer suffices to describe them (Schuster and Sigmund, 1982). 

Zimmerman and Briggs explain their dosage response curves on the basis of three independent pigment systems. However, for several reasons it appears more reasonable to ascribe their complicated patterns to different secondary rather than to distinct primary processes. First, the first and second positive curvatures show essentially the same action spectra (Fig. 3 4 and 5). Second, the Bunsen-Roscoe law holds only for the first 100 s of irradiation. After that time factors other than photochemical ones clearly govern phototropism. Third, the dosage response curves are not real kinetics, i.e. they do not represent continuous traces of bending in time, as the authors assume for their calculations. However, curvature was allowed to develop for 100 min in darkness, measured and plotted as a function of dosage. 

Although many pulse sequences have been investigated for 2-D NMR, only a very limited number are of practical interest. One deterrent to their more widespread use is the time required and hence the cost of collecting the data. The time factor arises because the pulse sequences have to be repeated hundreds of times whilst varying the time interval during the evolution period, t13 in order to provide sufficient data for the final 2-D contour plot. Three of the more valuable 2-D techniques are described below. 

The time factor is the duration of exposure, with the assumption that the shorter the exposure time, the less likely it is that an individual will suffer an ill effect. The distance factor is the physical separation (e.g., in feet or miles) between an individual and the location of the terrorist event. The shielding factor refers to physical barriers between an individual and hazardous substances emanating from the attack location. These three factors are discussed in detail below, along with general rules for minimizing exposure. 

Time in this context is duration to which an individual is exposed to a hazardous substance. Time is relevant because the longer an individual remains in the open or at the site of a terrorist attack, the more likely there will be an exposure to a hazardous substance. Time is also relevant because the longer an individual is in contact with a hazardous substance (e.g., on the skin), the larger the exposure. The time factor is applied whether an individual is directly at the site of the attack or only in the vicinity. However, the time factor is applied differently in these two cases. For example, if an individual is in the vicinity of the attack site, the following time factor rule applies ... 

Different rules apply to individuals at the site of an attack. They must be concerned about potential radiation exposure, inhalation of airborne contaminants, contamination on skin and clothing, and incidental ingestion of contaminated substances. For individuals at the site of an attack, the following time factor rules apply ... 

Everyone should avoid plumes of smoke that may deposit contaminants at larger distances. It would be unfortunate for an individual to safely evacuate from a terrorist attack only to be caught in the open a mile from the attack and exposed to a plume of contaminated smoke. As with the time factor, the best practice is to move quickly from the site of the attack and seek shelter in a building with the heating and air conditioning system either set to recirculate the existing air in the building or turned off. The next step is to wait for authorities to confirm when it is safe to evacuate the area. 

Chapter 4 described methods for limiting the time of exposure to weapons of mass destruction that utilize no explosives (e.g., aerosol delivery) or use of conventional explosives (e.g., dirty bomb). The basic procedure is to leave the contaminated area as quickly as possible, enter a nearby building to shelter against airborne contamination, remove soiled articles of clothing, and wash all exposed body parts (including the mouth and hair) as soon as possible. In Chapter 4, the time factor is applied primarily to limit the chances of potential future health effects. In this section, the time factor is applied after a nuclear explosion to prevent serious bodily harm and death. 

Consider the analysis of a blood sample for alcohol content (imagine that a police officer suspects a motorist to be intoxicated). The problem here is not sampling different locations within a system, but rather a time factor. The blood must be sampled within a particular time frame in order to demonstrate intoxication at the time the motorist was stopped. 

---