Working levels

Elemental fluorine and the fluoride ion are highly toxic. The free element has a characteristic pungent odor, detectable in concentrations as low as 20 ppb, which is below the safe working level. The recommended maximum allowable concentration for a daily 8-hour time-weighted exposure is 1 ppm. 

Biological limits are also in force for lead and its compounds under the Control of Lead at Work Regulations 1998 different blood lead action, and suspension from work, levels apply to women of reproductive capacity, young persons and other employees. 

The term inventory refers to liquid hydrocarbon contents at the top of the working level range. Tray holdup is included, but piping contents are disregarded. 

The enclosure is also capable of storing fume surges during bucket charging. With proper design, the top of the enclosure will fill with fume while the lower working level remains clear. The key to producing this effect is to reduce fume recirculation in the enclosure by proper placement of the air curtain with respect to the exhaust off-take. 

Working level (WL) The allowable level ot exposure of a person to an atmosphere that contains any combination of Radon daughters. 

Working level month (WLM) An exposure ot I WLM can be taken to be received by a person working in a Radon daughter concentration of 1 WL for 170 hours. 

It was shown above that the total erystal number, surfaee area and the mass mean size are affeeted by the mean residenee time and the rates of nueleation and erystal growth respeetively. Sinee both these kinetie proeesses depend upon the working level of supersaturation whieh will itself depend on the amount of surfaee area available and erystal mass deposited, the question arises what will be the effeet of a ehange in residenee time on erystallizer performanee Consider the idealized MSMPR erystallizer depieted in Figure 7.8. 

It has been shown that an increase in crystallizer residence time, or decrease in feed concentration, reduces the working level of supersaturation. This decrease in supersaturation results in a decrease in both nucleation and crystal growth. This in turn leads to a decrease in crystal surface area. By mass balance, this then causes an increase in the working solute concentration and hence an increase in the working level of supersaturation and so on. There is thus a complex feedback loop within a continuous crystallizer, illustrated in Figure 7.11. 

Cleanliness Based on British Standard 5295 measured at working level ... 

Two methods of preventing overheating are available either general ventilation to provide fairly even conditions over the whole space at working level or local ventilation to give spot cooling for localized hot spots. 

Next, the boiler must be passivated. The boiler is filled above normal working level and ammonia/hydrazine or a similar passivation treatment is added. The boiler is first given a hydrostatic test. Following this, the water level is dropped, and the boiler is lightly fired for 4 to 6 hours to ensure adequate passivation of the boiler surfaces. 

Working Level (WL)—Any combination of short-lived radon daughters in 1 liter of air that will result in the ultimate emission of 1.3x105 MeV of potential alpha energy. 

Working Level Month (WLM)—A unit of exposure to radon daughters corresponding to the product of the radon daughter concentration in Working Level (WL) and the exposure time in nominal months (1 nominal month =170 hours). Inhalation of air with a concentration of 1 WL of radon daughters for 170 working hours results in an exposure of 1 WLM. 

In our study, volunteers wearing either WBDs or bathing suits performed a set of choreographed Jazzercize routines on chlorpyrifos-treated carpet. These exercises at a low work level were designed to represent a maximum daily surface contact and transfer of chemicals such as pesticides. Results were similar to exposures of two sets of adults who used insecticide foggers in their homes. 

MeV. WL-R = 100% x WL/radon concentrations (pCi/1). The dose conversion factor of 0.7 rad/working level month (WLM) (Harley and Pasternack, 1982) was used to calculate the mean absorbed dose to the epithelial cells and a quality factor (OF) of 20 was applied to convert the absorbed dose to dose equivalent rate. For example, from the average value of (WL) obtained from the arithmetic mean radon concentrations measured in the living area during winter and summer in South Carolina (Table I), the calculated dose equivalent rate is 4.1 rem/yr, e.g.,... 

A survey of the radon concentrations in a representative sample of more than 2000 dwellings in the UK has been completed and provisional results are now available. On average, concentrations are 29% lower in bedrooms than in living areas. The mean radon concentration weighted for room occupancy is 22 Bq m 3. Assuming an equilibrium factor of 0.35 and a mean occupancy of 75%, the mean annual exposure in UK homes is assessed as 0.08 Working Level Months (WLM) and the mean annual effective dose equivalent as 0.43 mSv. 

An equilibrium factor of 0.35, derived from measurements made during the local surveys, has been assumed to typify conditions in UK dwellings. This value has been used to convert the average radon concentrations measured in the national survey to potential alpha-energy concentration of radon decay-products. On average, persons in the UK spend 75% of their time in their homes and 15% of their time elsewhere indoors (Brown, 1983). The occupancy factor of 0.75, together with an equilibrium factor of 0.35, results in an annual exposure of 1.3 10"5 J h m"3 (0.0037 Working Level Months,... 

Fleischer, R.L., Theory of Passive Measurement of Radon Daughter and Working Levels by the Nuclear Track Technique, Health Physics 47 263-270 (1984). 

Three different experimental protocols were used throughout the work. Two protocols were used to determine the activity size distribution, the first protocol, based on individual progeny, for the bulk of the measurement days (Jan 29 to Feb 6) and the second, based on Working Level, for the last two days (Feb 7 and 8). The third experimental protocol was used for general determination of Working Levels from Jan 29 to Feb 6. 

The radon progeny Working Levels for calculation of activity distributions were calculated using the equation ... 

The first sample of the day was counted at 270-285 minutes after sampling in order to allow counting to be completed in the underground working period. Equation (7) was used to calculate the thoron progeny Working Level in this case, with 1(330-345) replaced by 1(270-285). 

On the last two days, Working Levels determined by equations (6) and (7) for activity size distribution were used. 

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