Exposure Rate

Exposure rate is the measurement of workplace exposure of hazardous materials based upon tests conducted on laboratory animals. Values are translated to humans based on the weight ratio between an animal and a human. These are only estimations and should be used with caution. Toxicology information is expressed in parts per million (ppm) or billion (ppb) and milligrams per cubic meter (mg/m ), which are terms indicating the concentration of the toxic material. These terms are not related, 

Nervous system Skeleton and bone marrow Thyroid 

TLV-STEL Threshold limit value, short-term exposure hmit is the maximum concentration averaged over a 15-min period to which healthy adults can be exposed safely. Exposures should not occur more than four times a day, and there should be at least 60 min between exposmes. 

TLV-C or TLV-ceiling The concentration that should not be exceeded during any 

PEL The pemiissible exposure limit is the maximum concentration averaged over 8 hours, to which 95% of healthy adults can be repeatedly exposed for 8 hours per day, 40 hours per week. 

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Wollenberg, H.A., Naturally Occurring Radioelements and Terrestrial Gamma-ray Exposure Rates An Assessment Based on Recent Geochemical Data, Report LBL-18714, Lawrence Berkeley Laboratory, Berkeley CA (1984). 

In assessing total population dose it seems reasonable to assume that the exposure rate during the residual 15% of time spent indoors is the same as that received at home. 

The exposure rate characteristic for this atmosphere is then given by the potential alpha energy concentration (PAEC) Ep... 

Figure 1. Effect of filtration on radiological dose and exposure rate in an atmosphere with intermediate aerosol concentration.

It has been demonstrated that it is possible to lower the level of airborne radon progeny by filtering and/or expose the air to an electric field. If the radiological risk is measured by the potential alpha energy concentration (PAEC) or exposure rate, for instance expressed in J m 3 or WL, the level may be lowered to about 10-20 % of the value in untreated air, while the reduced level may only be about 40-50 % of the untreated one if the average dose to a certain part of the respiratory tract, for instance expressed in Gy year 1, is considered. 

The question of whether exposure rates or doses should be used in evaluating all types of remedial procedures has so far received very little attention. For reasons of convenience the PAEC is normally used, sometimes even estimated from the radon concentration assuming a rather arbitrarily chosen value of the equilibrium factor. It seems reasonable to assume that this in certain cases may give a rather misleading description of the radiological conditions. 

Cross,F.T., Palmer,R.F., Dagle,G.E., Busch,R.H., and R.L. Buschbom, Influence of Radon Daughter Exposure Rate, Unattached Fraction and Disequilibrium on Occurrence of Lung Tumors, Rad.Prot.Dosimetry 7 381 (1984). 

Cross, F., Palmer, R., F. and Busch, R., H., Influence of Radon Daughter Exposure Rate and Uranium Ore Dust Concentration on Occurrence of Lung Tumors, in Proc. of the Specialist Meeting on the Assessment of Radon and Radon Daughter Exposure and Related... 

Fig. 1. Heavy over light s-elements ratio versus metallicity. Lines are theoretical predictions for a 1.5M AGB stars with C/0=1.1 and three different choices for the neutron exposure rate (see Busso et al., 2001, ApJ, 557, 802). Black dots are for galactic carbon stars analyzed in Abia et al. (2002, ApJ 578, 817).

Table 4. Rainwater total salt content and salt deposition/exposure rates over various natural ecosystems in Eurasia.

The average sum of total ash elements in the biomass of Tropical Rain Forest ecosystems is about 8,000 kg/ha. The annual ash element turnover and heavy metal exposure rates are shown in Table 8. 

Table 13. Average biogeochemical exposure rates of heavy metals species in Mangrove ecosystems.

The comparison of biogeochemical fluxes and relevant exposure rates of heavy metals in the Mangrove and Tropical Rain Forest ecosystems shows that the total mass of ash elements per unit area is similar. However, the proportion of various elements is markedly different. The Mangrove plant uptake of Fe and Mn is less and that of Sr is higher than the uptake of these elements in Tropical Rain Forest ecosystems. 

The Mangrove ecosystems perform a role of biogeochemical barrier, which decreases significantly the runoff of chemical species from the coast to the ocean waters. This is correlated with the major biogeochemical parameters of these ecosystems such as high productivity and high values of annual biogeochemical fluxes and relevant exposure rates. 

The relevant changes in exposure rates are also of importance for predicting the behavior of Mangrove ecosystems and environmental risk assessment for their fate. 

Henderson, R.F., Barr, E.B. and Hotchkiss, J.A. (1991). Effect of exposure rate on response of the lung to inhaled particles, (abstr.) Toxicologists 11 234. 

A mutated cell may reproduce and begin the formation of a carcinogenic mass (tumor), and mutations may occur after acute or chronic exposure. The specific relationship between acute or chronic exposure rate and cancer risk is hotly debated, although current U.S. regulations conservatively adopted the linear no threshold (LNT) model. This model states that risk is linearly proportional to the total dose even at the smallest possible dose levels (risk is associated with all levels of dose no matter how small). An alternate model theorizes that no measurable adverse health effects appear below doses of about 10 to 25 rem (0.1 to 0.25 Sv). Data supporting both models are limited and, to be conservative, levels of exposure should be kept as low as reasonably achievable (ALARA). Victim and emergency responder doses and dose rate may not be easily controlled in the event of a terrorist attack. However, methods to achieve ALARA exposures are described in Chapters 4 and 5. 

After radiation, a strong upsurge in conductivity then decreased and leveled off after about an hour. This was analyzed in terms of trap filling, which showed a linear dependence on the exposure rate, X, at the radiation induced current Ir. For this polymer, mobility of the holes greatly exceeded that of electrons.(12) Additional studies done by electron pulse... 

Infants and toddlers are exposed to higher levels (based on their greater dose to surface area [or body weight] ratio) of heptachlor epoxide in the diet (particularly from milk) than are adults. Higher exposure rates in indoor air may occur for at least 1 year in homes that have been treated for termites with heptachlor in the past. Although the most likely routes of exposure at hazardous waste sites are unknown, exposure may result from ingestion of contaminated soil near these sites particularly by children. Since both heptachlor and heptachlor epoxide volatilize from soil, inhalation exposure may also be important for persons living near hazardous waste sites. Exposure via... 

Electron beam systems can be conveniently considered in two broad categories those using scanned, focused electron beams which expose the wafer in serial fashion, and those projecting an entire pattern simultaneously, onto a wafer. Electron beam projection systems have been investigated extensively since they offer the potential of higher exposure rates as a... 

SENSITIVITY Energy density Exposure rate Exposure environment Developing Post-exposure treatment Radiation efficiency Molecular weight... 

Cardiovascular Effects. The only information available is the case of an investigator who self-applied an amount of ointment containing 100 mg 1,3-DNB three times over a 24-hour period (White and Hay 1901). After the third application, he noticed that his heart rate had increased to about 100-120 beats per minute and did not return to pre-exposure rate (not specified) until 3 days later. No further information was provided. 

Calculating the dose following workplace or environmental exposure can be far more difficult. If the agent is in the air, then calculation of the dose must consider not only the concentration in the air but also the duration of the exposure, rate of breathing, and body weight. The amount of air inhaled over a period of time is... 

HERP value is the lifetime daily exposure rate experienced by humans (in milligrams per kilogram of body weight) that lowers, by one-half, the percent of tumor-free animals in a bioassay experiment over a standard lifetime of the animal. Asterisks imply that the substance acts as a promoter of cancer and is not genotoxic itself. 

Touring the formation of radioactive fallout particles, one of the most important processes is the uptake, in the cooling nuclear fireball, of the vaporized radioactive fission products by particles of molten soil or other environmental materials. Owing to the differences in the chemical nature of the various radioactive elements, their rates of uptake vary, depending upon temperature, pressure, and substrate and vapor-phase composition. These varying rates of uptake, combined with different residence times of the substrate particles in the fireball, result in radiochemical fractionation of the fallout. This fractionation has a considerable effect on the final partition of radioactivity, exposure rate, and radionuclides between the ground surface and the atmosphere. 

T he radioactive products of a nuclear explosion are said to have under-gone fractionation if their relative proportions in samples taken at various locations differ significantly from their relative proportions as formed. This report describes a study of fractionation in the early fallout from the nuclear cratering shots Danny Boy, Sedan, and Palanquin. Published fallout data for these shots was the basic information used in the study. A normalization procedure was applied to the published data as follows the amount of each radionuclide (or mass chain) of interest measured on a fallout tray is related to the gamma-radiation exposure rate measured at the tray location and to the amount of that radionuclide produced per kiloton of fission by the device. The result is an index... 

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