Personal monitors estimate

Noise. Technical differences exist between personal noise dosimeters and high accuracy sound level meters and these may alter the usual preference for personal monitors. But it is exposure to noise rather than general room noise that must be estimated for comparison with noise exposure criteria, the logarithmic expression and alternative means of summation (3 vs 5 db doubling) compHcate statistics. Exposure criteria for both dose and peak exposure must be evaluated, and space and time variabiUty of noise intensity can be immense. 

Heat. Personal monitoring of the environmental conditions which impose a heat stress on a worker is impractical, so fixed station measurement of such parameters as wet bulb globe temperature are usually made (see Temperature measurements). These stations are carefully selected so that the results, plus worker location and workload data, can be combined to yield an overall heat stress estimate. Heat strain, the effect on the human, can be estimated from core body temperature, but this is usually only a research tool. 

In many external exposure circumstances, dose equivalent estimates obtained from personal monitors significantly overestimate Hz or E, particularly when the body is not uniformly irradiated due to the irradiation conditions or due to protective shielding of portions of the body. Specifically in these cases, the numerical relationships between monitoring data and Hz or E need to be better understood, so that appropriate monitoring practices are selected and monitoring data are properly evaluated. 

Section 1 of the Report presents the quantities Hz and E and the relationship of each quantity to its corresponding radiation protection system. Section 2 describes the use of personal monitors for workers in the United States, including their calibration and how they are worn on individuals in various occupational settings. Section 3 discusses practical ways to use one or two personal monitors to obtain estimates of Hz and E. Section 4 provides the NCRP s... 

Estimating Effective Dose Equivalent or Effective Dose in Practice Using Personal Monitors... 

In scenarios for which the irradiation geometry in practice is difficult to determine, investigators have recommended the use ofii/pdO) values determined from multiple personal monitors to obtain improved estimates ofi/g (Lakshmanan et al., 1991 Xu, 1994). These investigators have demonstrated that i p(10) values from personal monitors placed on the front (i.e., center of the chest) and back (t.e., center of the back) of individuals can be combined in specific algorithms that yield closer estimates of than the values of 10)... 

This alternative is denoted the (70/30) algorithm and it minimizes the differences of the ratios of (estimatel/Hg from the value of 1.0. That is, if both under- and overestimates of Hz are equally acceptable in practice, this algorithm provides the minimal spread of these estimates around the Hz values. A Monte Carlo method was utilized to obtain the optimum weighting factors (i.e., 0.7 and 0.3) for the Hp(lO) values of the two personal monitors, with the sum of the weighting factors constrained to be equal to 1.0 (Claycamp, 1996). 

The values of He (estimate) are obtained from values of Hp(lO) consistent with the calibration procedures for personal monitors used in the United States (i.e., a 30 X 30 X 15 cm PMMA slab), and... 

Table 3.1— Ratio of He (estimate) to He for various irradiation geometries and combinations of Hp(10) values from personal monitors... 

Authors preferred algorithms for estimating from the H p(lO) values for the front and back personal monitors (see Section 3.2). 

ICRU and ICRP have a joint effort underway to review and present values of E for Monte Carlo calculations in anthropomorphic phantoms, but that work is not yet published. When the data are published, a similar evaluation of the use of Hp(10) values determined from two personal monitors to estimate E will be possible. 

Hw and Hn are the values ofHp(lO) for the personal monitors worn at the waist and neck, respectively. The formula results in values between 0.97 to 1.07 He for 0.5 mm lead equivalent aprons and between 1.12 to 1.72 He for 0.3 mm lead equivalent aprons. Use of the formula is a simple and practical way to estimate He when both personal monitors are worn. 

Table 3.6—Empirical formula and estimates for He using two personal monitors and the conversions derived from Faulkner and Harrison (1988), apron present, avertable x-ray tube (Webster, 1989).

Table 3.7—Empirical formula and estimates for E using two personal monitors, derived from Faulkner and Marshall (1993) and Rosenstein and Webster (1994),...

Use of Personal Dose Equivalent for Strongly-Penetrating Radiation Values Determined from Two Personal Monitors to Estimate Effective Dose Equivalent... 

When a single personal monitor worn at the neck outside and above a protective apron is used, dividing/In, [i.e., the i/p(10) value for this personal monitor] by 5.6 to obtain a conservatively high estimate of He is recommended. Likewise, dividing/In by 21 to obtain a conservatively high estimate ofE is recommended. These modifications ofHti give appropriate credit for the protection afforded by the apron and do not overestimate the value of He by more than a factor of three or the value of E by more than a factor of 3.4. 

When two personal monitors are used, one worn under a protective apron at the waist or on the chest [where /fw is the //p(10) value for this personal monitor] and the other worn outside and above the apron at the neck, it is recommended that the value of He be estimated from the formula ... 

Use of Personal Monitors to Estimate Effective Dose Equiva-... 

USE OF PERSONAL MONITORS TO ESTIMATE EFFECTIVE DOSE EQUIVALENT AND EFFECTIVE DOSE TO WORKERS FOR EXTERNAL EXPOSURE TO LOW-LET RADIATION... 

Use of personal monitors to estimate effective dose equivalent and effective dose to workers for external exposure to low-LET radiation, p. cm.—(NCRP report no. 122)... 

This Report is one of the series developed under the auspices of Scientific Committee 46, a scientific program area committee of the National Council on Radiation Protection and Measurements (NCRP) concerned with operational radiation safety. The Report provides practical recommendations on the use of personal monitors to estimate effective dose equivalent (Hg) and effective dose (E) for occupationally-exposed individuals. The Report is limited to external exposures to low-LET radiation. Recent additions to the radiation protection literature have made the recommendations possible. In order to avoid delay in utilizing the recommendations in the United States, the quantity as well as E, has been included until such time as the federal radiation protection guidance and associated implementing regulations are revised to express dose limits in E as recommended by the NCRP. 

Use of Personal Monitors to Estimate Effective Dose Equivalent and Effective Dose to Workers for External Exposure to Low-LET Radiation (1995)... 

OSHA requires employers of workers who are occupationally exposed to 2-butoxyethanol to institute engineering controls and work practices to reduce employee exposure and maintain it at or below pennissible exposure limits (PEL). The PEL for 2-butoxyethanol is 50 ppm (OSHA 1974). Workers exposed to 2-butoxyethanol should wear personal protective equipment such as gloves, coveralls, and goggles to protect exposure to tire skin (OSHA 1974). NIOSH recommends that industrial hygiene surveys be completed at work places where airborne exposure to 2-butoxyethanol or 2-butoxyethanol acetate may occur (NIOSH 1990). If exposure levels are at or above one-half the recommended exposure limit (REL = 5 ppm), NIOSH recommends that a program of personal monitoring be instituted so that tlie exposure of each worker can be estimated. If exposure levels are at or greater than the REL, or if there is a potential for skin contact, NIOSH recommends that 2-butoxyacetic acid be measured in the urine of the workers. 

Exposure assessment estimates the number of exposed persons together with the magnitude, duration and frequency of exposure. A direct possibility to measure the human exposure to toxic substances via ambient air, for example, is the utilization of personal monitors. 

In order to get instantaneous results, continuous filter tape instruments have been developed based on modification of the colorimetric Marcali method. The instruments have been used for continuous air monitoring of production sites and for personal monitoring of isocyanates. A limitation with the filter tape instruments is that no compound-specific information is given in means of retention times or detector specific structural information. Since the instruments have to be calibrated for the different isocyanates, quantitative estimation of mixed isocyanate exposures is troublesome. Problems associated with influence of interfering compounds, humidity, and collection of particles have been reported. " ... 

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