Nominal protection factor

The nominal protection factor (NPE) describes the level of protection afforded by a specific respirator ... 

Table 11.18 Nominal protection factors of respirators and breathing apparatus...

The British Standard BS 4275 gives guidance on the selection, use and maintenance of respiratory protective equipment. The nominal protection factor (npf) measures the theoretical capability of respiratory protection and is used in the selection of equipment. 

The degree of protection required will be the factor by which it is necessary to reduce the airborne concentration of the contaminant in order to limit the exposure to below the occupational exposure limit. A fraction of the OEL, i.e. one-tenth, is usually chosen as a suitable level of protection. The degree of protection provided by a specified piece of RPE is given by a designated nominal protection factor (NPF), which is defined as the ratio of the concentration of contaminant present in the ambient atmosphere to the calculated concentration in the breathing zone when the RPE is being worn. 

Table 1. Approximate Nominal Protection Factors (NPF) for Various Types of Respiratory Protective...

To make proper selection of any type of RPE, an Indication is needed of Its likely efficiency, when used correctly. In relation to the hazard guarded against. The technical term used in respiratory protection standards to define the equipment s capability is the nominal protection factor, or NPF. For each class of equipment, it is the total Inward leakage requirement set for that class, and therefore does not vary between products meeting the class standards. Manufacturers will supply information on the NPF for their product range — it is the simple ratio between the contaminant outside the respirator (in the ambient air) and the acceptable amount inside the facepiece. Examples of typical NPFs are ... 

Several types of respiratory protective equipment may have the necessary ratio of assigned protection factor to nominal protection factor when predictions and/or measurements have been made of the physical form and concentration of contamination in the workplace. The choice could include all types of respiratory... 

The surface dose rate through the nominal protective layer of skin (7 mg/cm ) from a thin uniform deposit of 1 pCi/cm is about 9 rad/hour for beta energies above about 0.6 MeV. Note that in a thin layer, the beta dose rate exceeds the gamma dose rate, for equal energies of emission, by about a factor of 100. 

It was recently reported that the application of a protective polarization may be avoided by using corrosion-resistant activated electrodes [32], The polarization protection of the electrodes represents approximately 1-2% of the nominal electrolyzer power. Assuming the capacity factor of the electrolyzer cannot exceed the one of the wind turbine, the polarization protection should be applied during 60% of the electrolyzer s lifetime or higher depending on the relative sizes of the electrolyzer and wind turbine. 

Instantaneons overcnrrent protection wonld detect short circnits in the load and along its feeder cable. It wonld nsnally be practical to set the instantaneons elements of a monlded case circnit breaker to their lowest valne e.g. five times the nominal cnrrent. If the protection is provided by a set of fnses then the fnsing factor wonld be marginally above nnity, the nearest fnse rating above the load cnrrent would be chosen. The protection must fully cover the Pt capacity of the feeder cable. 

The second and preferred method is to apply appropriate statistical analysis to the dataset, based on linear regression. Both EU and USFDA authorities assume log-linear decline of residue concentrations and apply least-squares regression to derive the fitted depletion line. Then the one-sided upper tolerance limit (95% in EU and 99% in USA) with a 95% confidence level is computed. The WhT is the time when this upper one-sided 95% tolerance limit for the residue is below the MRL with 95% confidence. In other words, this definition of the WhT says that at least 95% of the population in EU (or 99% in USA) is covered in an average of 95% of cases. It should be stressed that the nominal statistical risk that is fixed by regulatory authorities should be viewed as a statistical protection of farmers who actually observe the WhT and not a supplementary safety factor to protect the consumer even if consumers indirectly benefit from this rather conservative statistical approach. 

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