Excursion factors

The TLVs for airborne contaminants are based on the premise that although all chemical substances are toxic at some concentration for some period of time, a concentration exists for all substances from which no toxicity may be expected no matter how often the exposure is repeated. A similar premise holds for substances producing irritation, discomfort and nuisance. In using these limits, items such as excursion factors, ceiling values, "skin" notations, mixtures of substances, and inert material should be considered. These factors are discussed below. 

The limiting excursion factors should be considered "rule-of-thumb" guidelines for listed substances, but are not appropriate for all materials (such as those designated "C"). 

Maximum values measured were 63.7 and 33.9 mg/w which corresponds to an excursion factor of 12.7 and 6.8 re p tively. 

Short-Term Exposure Limit, STEL, is a 15-minute TWA concentration that may not be exceeded, even if the 8-hour TWA is within the standards. TWA-STEL are given for contaminants for which short-term hazards are known. For the rest, an excursion factor of 3 has been often used STEL should not exceed 3 times the TWA limit. ... 

It is a property of this family of differential equations that the sum or difference of two solutions is a solution and that a constant (including the constant i = / ) times a solution is also a solution. This accounts for the acceptability of forms like A (t) = Acoscot, where the constant A is an amplitude factor governing the maximum excursion of the mass away from its equilibrium position. The exponential form comes from Euler s equation... 

Criticality Precautions. The presence of a critical mass of Pu ia a container can result ia a fission chain reaction. Lethal amounts of gamma and neutron radiation are emitted, and a large amount of heat is produced. The assembly can simmer near critical or can make repeated critical excursions. The generation of heat results eventually ia an explosion which destroys the assembly. The quantity of Pu required for a critical mass depends on several factors the form and concentration of the Pu, the geometry of the system, the presence of moderators (water, hydrogen-rich compounds such as polyethylene, cadmium, etc), the proximity of neutron reflectors, the presence of nuclear poisons, and the potential iateraction with neighboring fissile systems (188). As Httle as 509 g of Pu(N02)4 solution at a concentration Pu of 33 g/L ia a spherical container, reflected by an infinite amount of water, is a critical mass (189,190). Evaluation of criticaUty controls is available (32,190). 

The effect of pulsating flow on pitot-tube accuracy is treated by Ower et al., op. cit., pp. 310-312. For sinusoidal velocity fluctuations, the ratio of indicated velocity to actual mean velocity is given by the factor /l + AV2, where X is the velocity excursion as a fraction of the mean velocity. Thus, the indicated velocity would be about 6 percent high for velocity fluctuations of 50 percent, and pulsations greater than 20 percent should be damped to avoid errors greater than 1 percent. Tne error increases as the frequency of flow oscillations approaches the natural frequency of the pitot tube and the density of the measuring fluid approaches the density of the process fluid [see Horlock and Daneshyar, y. Mech. Eng. Sci, 15, 144-152 (1973)]. 

In addition, it may be necessary to limit permissible upward excursions from the TWA. In practice, concentrations of chemical agents in workplace air fluctuate frequently and to a considerable extent. The amount by which the OEL-TWA may be exceeded for short periods without impairment of health depends upon several factors, such as the nature of the substance, the frequency with which high concentrations occur, and the duration of such periods. 

Figure 25a, as an example, shows the potential dependence of the single-junction conductances of 44-BP measured in 0.1 M HCIO4 solution (pH 1) in —0.10 V < E < 0.90 V in a semi-logarithmic representation. The values of L, M, and H decrease with more positive electrode potentials, and follow nearly the same trend for each family. The single-junction conductances decrease by a factor of 3-5 upon potential excursion towards positive values in the accessible potential region. A similar trend is also observed for electrolytes with variable pH ranging between 1 and 10, as... 

In the preceding discussion, we have calculated the attenuation factors for 10Be for three periods, 200, 7 x 103 and 10s years. Of these the 200 and 7000 year periods are well established and have been ascribed to solar cycle variations and earth s magnetic field excursions, respectively. For detailed calculations on the effect of these variations on the production rates of isotopes by cosmic rays reference is made to Castagnoli and Lal, 75.)... 

Slow periodic variation of the T plot are usually the result of uncontrolled environmental factors. Seasonal variations related to poor laboratory temperature control have been frequently identified by this pattern. Instruments are seldom sensitive to small ambient temperature changes. However, if an instrument is operating near its suggested nominal operating temperature short term excursions from this temperature can affect both accuracy and precision. CYCLES in the T plots are usually accompanied by similar behavior in the D plots. 

A very profound temperature effect was observed for the emission intensity. Figure 1 presents an emission-temperature profile at open circuit in sulfide electrolyte the relative invariance of the sample s spectral distribution with temperature allowed us to monitor emission intensity at the band maximum. Emission intensity was matched for 501.7 and 514.5 nm excitation at 20°C using 17 times as much 501.7 nm intensity. Over the 20-100°C excursion emission intensity is seen to drop by factors of 8 and 30 for 501.7 and 514.5 nm excitation, respectively. 

Our starting point is the decomposition of the normal modes of a larger system into those of independently computed fragments [12], An exact decomposition is possible if the number of the nuclei of the fragments equals those of the supersystem, and provided all normal modes are considered, which means rotations and translations must be included in the treatment. In order to avoid the otherwise ubiquitous mass factors, it is convenient to use the matrix L which gives the transformation between the mass-weighted excursions of the nuclei a and the normal modes Qp, rather than Lx. The elements of the two matrices are related by Laip = /mJtLxai p [59], A normal mode Lsp of the system S can be written as linear combination of the normal modes Lf, Lf, Lcr of the independent subunits A, B, C - - with the numbers NA, NB, Nc - of nuclei ... 

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