Safety factor judgmental

OSHA has warned compliance personnel to use a great deal of professional judgment regarding mathematical approaches. OSHA believes that the results should incorporate reasonable safety factors and be interpreted conservatively. 

The Lehman-Fitzhugh approach has been very widely used for setting limits on exposures to chemicals, not only in food, but in all other environmental media, but it has undergone significant refinement in recent years. The EPA, and others, for example, now uses the term uncertainty factor for those factors that reflect a true scientific uncertainty, and distinguishes these from safety factors, which reflect the injection of policy judgments that go beyond scientific uncertainties in the establishment of acceptable intakes. The EPA has dropped the... 

C] is a nonscientific, judgmental safety factor, i.e., a social or political value judgment. The default value is 1, indicating that no additional MOS is needed over that provided by the inherently conservative procedure above. 

The original use of the safety factor approach in regulation was by Lehman and Fitzhugh (13), who considered that animals may be more resistant to the toxic effects of some chemicals than humans are. They proposed the use of a factor of 10 when extrapolating from animals to humans and the use of another factor of 10 to account for differential sensitivities within the human population (13). These are not, however, rigid rules, and they should be applied with a strong infusion of scientific judgment. 

WEIL, C.S. (1972). Statistics versus safety factors and scientific judgment in the evaluation of safety for man, Toxicol. Appl. Pharmacol. 21, 454-463. 

The safety factor Itself may vary, depending upon the nature of the test data available and on other Judgmental factors. When long-term animal studies are available, the 100-fold safety factor generally Is applied. The food additive procedural regulations (21-CFR 170.22) refer to a safety factor of 100 to 1 in applying animal test data to humans. Exceptions to the 100-fold safety factor may be allowed for certain substances and under certain circumstances of use for example, in the case of micronutrients or macronutrients, or when information on dose-response effects in humans Is available. 

Safety factors have not been discussed inasmuch as these factors should reflect the engineer s confidence in the data he or she has, the distillation system performance deduced in manipulating these data, the reliability the equipment must demonstrate etc., in short, engineering judgment. There is never anything better than reliable experimental data on the system which is to be distilled, of course. In other, less-well-defined circumstances, conservatism is advised (9). Batch stills are usually (at least relatively) low-cost items, and increased capabilities represent small incremental costs. 

The safety factor used in the calculations is a matter of judgment based on confidence in the design. A value of 1.10 is normally not considered excessive. Typical design parameters are shown in Tables 11-1 and 11-2. 

In an expanding industry, it may be the policy to deliberately oversize critical equipment that cannot be modified for increased capacity. The safety factors in Table 1.3 account for future trends however, considerable judgment must be exercised to provide reasonable chances of equipment operating without unreasonably increasing capital investment. 

In the original safety assessment paradigm a single safety factor (SF) of 100 was used to derive an ADI from a NOEL. The justification of the SF (also called an uncertainty factor (UF)) was based on scientific considerations as well as a judgment about how to manage the inherent uncertainty associated with the... 

Health organizations throughout the world utilize a safe dose concept in the dose-response assessment of noncancer toxicity. This safe dose has often been referred to by different names, such as acceptable daily intake (ADI), tolerable daily intake (TDI) or tolerable concentration (TC), minimal risk level (MRL), reference dose (RfD), and reference concentration (RfC). The approaches used by various health organizations share many of the same underlying assumptions, judgments on critical effect, and choices of uncertainty (or safety) factors. 

There are many factors which contribute to the accuracy with which a safety factor may be determined. The most important is the accuracy of the soil formation properties used in the computation for safety factor. In fact, it is more realistic to consider the computed value as an estimated value rather than a very accurate one. Although mathematical attempts have been made to determine the range of error in an estimated safety factor, the proposed equations still depend upon an estimate of formation properties. In the end we must still rely heavily on engineering judgment. 

Predicting losses is difficult, particularly losses through and around doors, jamb, sills, tramp air, cooling losses, and losses through conveyor equipment and gaps around it. Assigning safety factors or security factors to cover these matters requires experience and careful judgment. 

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