Safety factors setting

All the other equipment must comply to the essential requirements. These are rather detailed, some are of a more descriptive nature. They contain precise requirements in particular with respect to the capability of a manufacturer and to a set of safety factors for the most common pressure equipment. 

Finally, under the heading Specific pressure equipment requirements specific requirements are set out for equipment with a risk of overheating, for piping and, last but not least, specific quantitative requirements which set out a series of safety factors for certain pressure equipment. These latter provisions apply as a general rule which means that a manufacturer or a harmonised standard may deviate from these factors if it can be demonstrated that appropriate measures have been taken to achieve an equivalent level of safety. 

Health and Safety Factors. Animal-feeding studies of DMPPO itself have shown it to be nontoxic on ingestion. The solvents, catalyst, and monomers that are used to prepare the polymers, however, should be handled with caution. Eor example, for the preparation of DMPPO, the amines used as part of the catalyst are flammable toxic on ingestion, absorption, and inhalation and are also severe skin and respiratory irritants (see Amines). Toluene, a solvent for DMPPO, is not a highly toxic material in inhalation testing the TLV (71) is set at 375 mg/m, and the lowest toxic concentration is reported to be 100—200 ppm (72). Toxicity of 2,6-dimethylphenol is typical of alkylphenols (qv), eg, for mice, the acute dermal toxicity is LD q, 4000 mg/kg, whereas the acute oral toxicity is LD q, 980 mg/kg (73). The Noryl blends of DMPPO and polystyrene have PDA approval for reuse food apphcations. 

The normal procedure to set design ratings for the blower is to calculate the blower design discharge pressure required for the design flow. Applying whatever safety factor is considered necessary, a design... 

The best anti-surge control is the simplest and most basic that will do the job. The most obvious parameter is minimum-flow measurement, or if there is a relatively steep pressure-flow characteristic, the differentia pressure may be used. The latter parameter allows for a much faster response system, as flow measurement response is generally slow however, the speed of response need only be fast enough to accept expected transients. One major problem with the conventional methods of measurement and control is the need to move the set point for initiation of the control signal away from the exact surge point to allow some safety factor for control response time and other parameters not directly included... 

Toxicologists tend to focus their attention primarily on c.xtrapolations from cancer bioassays. However, tlicrc is also a need to evaluate the risks of lower doses to see how they affect the various organs and systems in the body. Many scientific papers focused on tlic use of a safety factor or uncertainty factor approach, since all adverse effects other than cancer and mutation-based dcvclopmcnUil effects are believed to have a tlu cshold i.e., a dose below which no adverse effect should occur. Several researchers have discussed various approaches to setting acceptable daily intakes or exposure limits for developmental and reproductive toxicants. It is Uiought Uiat an acceptable limit of exposure could be determined using cancer models, but today tliey arc considered inappropriate because of tlircsholds. ... 

SF = safety factor to account for dynamic loads when slips are set on moving drill pipe (SF = 1.1)... 

Step 1. Determine the lightest weight of casing to resist collapse pressure for a setting depth of 12,000 ft. Because the maximum collapse pressure is (12,000)(0.52) = 6,240 psi, select N-80, 29-lb/ft casing with collapse pressure resistance of 7,020 psi. (Note assumed safety factor for collapse = 1.0.) This is Section 1. 

In the case of the ASME codes for nuclear pressurised components, the questions of fatigue design and of flaw evaluation are dealt with separately in ASME Section III and Section XI Appendix A, respectively. The design S-A curve for machined butt welds typical of thick section pressurised components is set at a factor of two on stress range or twenty on cyclic life, whichever is more conservative, below the mean of S-N data developed on smooth cylindrical specimens in air. (A somewhat similar design curve obtained by a different method from experimental S-A data for machined butt welds is given in British Standard 5500.) These safety factors are intended to encompass any adverse influence of minor weld defects, size effects, data scatter and environment. As far as environmental effects are... 

There are no hard-and-fast rules to follow in setting safety factors for any given material unless experience exists. The most important consideration is of course the probable consequences of failure. For example, a little extra deflection in an outside wall or a hairline crack in one of six internal screw bosses might not cause concern, but the failure of a pressure vessel or aircraft wing might have serious safety or product-liability implications. 

The easiest means for assessing occupational exposure hazards associated with materials used in a process is through the use of Permissible or Occupational Exposure Limits (OEL or PEL) which go by a variety of names for example, TLV (U.S. - American Conference of Government Industrial Hygienists), MAK (Germany), or individual company established values. Occupational exposure limits are usually set based on a combination of the inherent toxicological hazard of a chemical and a series of safety factors such as intraspecies variability in test results, nature and severity of the effect, adequacy and quality of... 

An added ten-fold safety factor shall be added in setting pesticide reference doses (RfDs) (i.e. acceptable daily intakes) to account for the unique risks faced by infants and children, unless the EPA administrator has solid data supporting a determination that existing RfDs are fully health protective, even for infants and that exposures are fully and accurately characterized and... 

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... 

ERA concludes that the maximum amounts of heptachlor and heptachlor epoxide present in your drinking water and in the seafood you eat each day through your lifetime should not exceed 2.78 ppt. In theory, this would limit the risk of developing cancer to one in 100,000. For contaminated seafood alone, the maximum amounts of heptachlor and heptachlor epoxide that your consume each day throughout your lifetime should not exceed 2.85 ppt. This recommendation is made because harmful effects may occur in people after exposure to heptachlor. Because the exact levels that might cause these effects are not known, ERA has set a very low limit as a safety factor. 

Residue must be < 0.1 ppm in meat and < 10 ppb in milk and eggs. + - If teratogenic activity is demonstrated, the safety factor is 1,000 may also be < 100 when human exposure data are available or when a sensitive measurement is used to set a no-effect concentration. 

The question of an extra assessment factor in the hazard and risk assessment for chemicals of concern for children is specifically addressed in Section 5.2.1.13. The U.S. Food Quality Protection Act (FQPA) (US-EPA 1996) directed the US-EPA to apply an extra safety factor of 10 in assessing the risks of pesticides to infants and children. The US-EPA (2002) noted the overlap of areas covered by the FQPA factor and those addressed by the traditional UFs, and it was concluded that an additional UF (children-specific) is not needed in the setting of reference values because the currently available UFs (interspecies, intraspecies, LQAEL-to-NOAEL, subchronic-to-chronic, and database-deficiency) were considered sufficient to account for uncertainties in the database from which the reference values are derived. Renwick et al. (2000) concluded that the available data did not provide a scientific rationale for an additional 10-fold UF for infants and children and pointed out that when adequate reproduction, multigeneration, or developmental studies are conducted, there will be no need for an additional 10-fold factor. 

With respect to veterinary medicines, the US-FDA establishes tolerances to include a safety factor to assure that the drug will have no harmful effects on consumers of the food product. The US-FDA first determines the level at which the dmg does not produce any measurable effect in laboratory animals. From this, the US-FDA determines an acceptable daily intake (ADI), and the drug tolerance and withdrawal times are then determined so that the concentrations of dmg residues in edible tissues are below the ADI. Depending on the dmg, safety factors of between 100-fold to 2000-fold are included in the calculations used to set the tolerances. 

The cure of thermoset resins involves the transformation of a liquid resin, first with an increase in viscosity to a gel state (rubber consistency), and finally to a hard solid. In chemical terms, the liquid is a mixture of molecules that reacts and successively forms a solid network polymer. In practice the resin is catalyzed and mixed before it is injected into the mold thus, the curing process will be initialized at this point. The resin cure must therefore proceed in such a way that the curing reaction is slow or inhibited in a time period that is dictated by the mold fill time plus a safety factor otherwise, the increase in viscosity will reduce the resin flow rate and prevent a successful mold fill. On completion of the mold filling the rate of cure should ideally accelerate and reach a complete cure in a short time period. There are limitations, however, on how fast the curing can proceed set by the resin itself, and by heat transfer rates to and from the composite part. 

The 1997 consultation addressed the topic of safety factors, which is vitally important for die protection of public health. Setting MRLs is in fact based on a series of assumptions. One assumption is that humans are at least as sensitive as the most sensitive laboratory animal to a potentially toxic residue. Another assumption is diat all the residues covered by the MRLs are as toxic as the parent substance. A third assumption is that residues free from the human gastrointestinal tract are all totally bioavailable. A fourth assumption is the safety factor used to infer an ADI from a NOEL, including the additional safety factor, generally with a value of 2, to establish a provisional ADI until further information is available to convert this into a definite ADI. Other assumptions are the overestimation of consumer exposure to drug residues and the reduction of MRL values to take account of normal conditions under which the veterinary drugs are administered. 

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