Attenuation or Moderation

Many of the incidents in this book were the result of leaks of hazardous materials, and the recommendations describe ways of preventing leaks by providing better equipment or procedures. As we have seen, equipment can fail or can be neglected, and procedures can lapse. The most effective methods, therefore, of preventing leaks of hazardous materials are to use so little that it hardly matters if it all leaks out (intensification or minimization) or to use a safer material instead (substitution). If we cannot do this and have to store or handle large amounts of hazardous material, we should store or handle it in the least hazardous form (attenuation or moderation). Plants in which this is done are said to be inherently safer because they are not dependent on added-on equipment or procedures that might fail the hazard is avoided rather than controlled, and the safety is inherent in the design. 

Attenuation or Moderation Another alternative to intensification is attenuation, or using a hazardous material under the least hazardous conditions. Thus large quantities of liquefied chlorine, ammonia, and petroleum gas can be stored as refrigerated liquids at atmospheric pressure instead of under pressure at ambient tempera-... 

Intensification. Reduce or ehminate hazardous materials or hazardous conditions. Substitution. Replace hazardous materials or conditions with safer ones. Attenuation or moderation. Use a hazardous material under less hazardous conditions. 

Attenuation, or moderation (principle 3), means reducing the severity of operation. If the use of a hazardous chemical in a process is unavoidable, then one needs to determine whether the severity of its usage could be moderated by operating the process at a lower pressure or temperature. Chlorine and ammonia can be... 

Many workers have measured microwave properties of blends of CPs with thermoplastics or with materials such as teflon. Fig. 12-6 shows e and e for P(Py)/teflon blends measured at 2 GHz by Lafosse [342]. It is seen that the rise in permittivity closely approximates the percolation threshold for DC conductivity, and that for the more conductive blends (P(Py)> ca. 0.15) the Loss Tangent is of the order of 10, indicating good absorption. Hourquebie et al. [483] studied P(Py) blends with a butyl elastomer, an epoxy, and teflon emulsion, and showed that a plot of log(e") vs. log(frequency) was linear over the 130 MHz to 18 GHz range their data however showed attenuation to be poor or moderate. In a study of P(Py) "latexes", Henry et al. [484] obtained typical values of e and e" at 5 GHz of ca. 945 and 1086. In a study of P(Py) blends with PVC, Jousse et al. [340] observed that for a pressed blend, classical microwave behavior, i.e. a monotonic fall of permittivities with frequency (Fig. 12-7a) is observed, whilst for injection-molded blends (Fig. 12-7b)... 

Moderate Use less hazardous conditions, a less hazardous form of a material, or facilities which minimize the impact of a release of hazardous material or energy (also called Attenuation and Limitation of Effects). 

Moderate means using materials under less hazardous conditions, also called attenuation. Moderation of conditions can be accomplished by strategies which are either physical (lower temperatures, dilution) or chemical (development of a reaction chemistry which operates at less severe conditions). 

Omalizumab is a recombinant humanized monoclonal anti-IgE antibody that inhibits binding of IgE to receptors on mast cells and basophils, resulting in the inhibition of mediator release and attenuation of the early- and late-phase allergic response. It may be a treatment option for moderate to severe persistent asthmatics 12 years of age or older whose asthma is not controlled by inhaled corticosteroids and who have a positive skin test or in vitro reactivity to perennial allergens.37 Omalizumab significantly decreases inhaled corticosteroid use, number and length of exacerbations, and increases asthma-related quality of life.37... 

Primary therapy is based on disease severity and type of hemorrhage.7 Most patients with mild to moderate disease and a minor bleeding episode can be treated with l-desamino-8-D-arginine vasopressin [desmopressin acetate (DDAVP)], a synthetic analog of the antidiuretic hormone vasopressin. DDAVP causes release of von Willebrand factor (vWF) and factor VIII from endogenous storage sites. This formulation increases plasma factor VIII levels by three- to fivefold within 30 minutes. The recommended dose is 0.3 mcg/kg intravenously (in 50 mL normal saline infused over 15 to 30 minutes) or subcutaneously or 300 meg intranasally via concentrated nasal spray every 12 hours. Peak effect with intranasal administration occurs 60 to 90 minutes after administration, which is somewhat later than with intravenous administration. Desmopressin infusion may be administered daily for up to 2 to 3 days. Tachyphylaxis, an attenuated response with repeated administration, may occur after several doses.8... 

The concentrations of other metals attenuate when the metals sorb onto the surfaces of precipitating minerals (see Chapter 10). Hydrous ferric oxide, the behavior of which is well studied (Dzombak and Morel, 1990), has a large specific surface area and is capable of sorbing metals from solution in considerable amounts, especially at moderate to high pH HAO may behave similarly. The process by which hfo or HAO form and then adsorb metals from solution, known as coprecipitation, represents an important control on the mobility of heavy metals in acid drainages (e.g., Chapman etal., 1983 Johnson, 1986 Davis etal., 1991 Smith et ai, 1992). 

Hydralazine is generally reserved for moderately hypertensive ambulatory patients whose blood pressure is not well controlled either by diuretics or by drugs that interfere with the sympathetic nervous system. It is almost always administered in combination with a diuretic (to prevent Na+ retention) and a p-blocker, such as propranolol (to attenuate the effects of reflex cardiac stimulation and hyperreninemia). The triple combination of a diuretic, -blocker, and hydralazine constitutes a unique hemodynamic approach to the treatment of hypertension, since three of the chief determinants of blood pressure are affected cardiac output (p-blocker). 

In summary, we should realize that, when applying Kioi values determined at high concentrations or derived from LFERs such as Eq. 9-26 (Table 9.2), we may underestimate equilibrium sorption at low concentrations (i.e., below 1% of the compound s solubility) by a factor of 2 or more. Due to competition with other sorbates present in a natural system, the effect of specific adsorption could, however, be significantly attenuated (Chiou et al., 2000). Furthermore, the abundance of specific adsorption sites may be rather low in certain environments. Hence, in cases in which the effect can be expected to be moderate and in which we need only to get an order of magnitude estimate of Kioc, we may decide to neglect the nonlinearity of the isotherm. In other situations, however, such as the PAH case discussed in Illustrative Example 9.3, adsorption to carbonaceous materials or other high-affinity sorbents present in significant abundances has to be taken into account. 

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