Ventilation rate factor

Nevertheless, it should not be concluded that any substance with a degree greater than 100% creates an inflammable environment. There is an environmental factor that was not taken into account here, which is the quantity of substance handled, the ventilation rate of the premises and the vapourisation speed of the liquid. This last factor is recommended by regulations but there are few figures available. These values are determined in conditions that cannot be compared with each real condition and are related to substances of different natures that cannot allow any direct comparison. 

Exposure and Bioavailability Issues. Primary routes of exposure to lead are via inhalation and ingestion. Lead exposure occurs through inhalation of airborne lead particles with deposition rates in adults of 30%-50% depending on factors such as particle size and ventilation rate (EPA 1986). Once deposited in the lower respiratory tract, lead appears to be almost completely absorbed (Morrow et al. 1980). 

Here we have only discussed the concentration of the radon gas. This is because the measurements have been made of this nuclide. However, the health effects are referred to the short-lived decay products. The equilibrium factor depends on the ventilation rate and the particle concentrations. 

The ventilation rate has decreased since the 1950s indicating a higher equilibrium factor and thereby a higher radon daughter increase since the 1950s than the increase of the radon gas concentration. How the particle concentrations have changed is not known. 

Figure 5. Relative standard deviation on the fitting of the deposition rate of the unattached daughters (Xun) and on the fitting of the ventilation rate (Xvent)> calculated by means of a Monte- Carlo simulation model. The lower curve is obtained with counting statistics alone. The upper curve includes one hour time fluctuations on the input parameters, with 10% rel. stand, dev. on X, un (15/h), a(.35/h), Vent(.45/h) and radon cone. (50 bq/m ) and 2% on recoil factor (.83), penetration unattached (.78) and flow rate (28 1/min).

In Figure 8 the doses per unit radon concentration are plotted as a function of the measured ventilation rate. The NEA conversion factor for low and moderate ventilation (NEA,1983, table 2.10) is multiplied by the appropriate equilibrium factor. In the figure no influence of the ventilation rate on the doses is found. 

Figure 8. Effective dose equivalent per hour and per unit radon concentration (A J B, V J-E) versus ventilation rate. The NEA conversion factor is multiplied by the mean equilibrium factor of the measurements indicated in the ventilation interval.

Equations 3-9, 3-12, and 3-14 are used to compute the ventilation rates required. Table 3-12 lists values for k, the nonideal mixing factor used with these equations. 

An MRL of 6 ppm has been derived for intermediate-duration inhalation exposure to hexachloroethane. This MRL is based on the 6-week study in rats by Weeks et al. (1979) in which tremors were observed at 260 ppm but not at 48 ppm. Based on the NOAEL of 48 ppm for neurological effects observed in the 6-week study (Weeks et al. 1979), an intermediate inhalation MRL was calculated by adjusting the NOAEL to an HEC of 174 ppm using reference ventilation rates (rat, 0.245 m3/day human, 20 m3/day) and body weights (rat, 0.236 kg human, 70 kg) from EPA (1988a) and by dividing by an uncertainty factor of 30. A factor of 3 was used to extrapolate from animals to humans, and a factor of 10 was used to account for human variability. 

However, some effects are less intuitively obvious, and have been neglected. Unstirred layer formation can have large effects on solute transport, and, on a minute-by-minute basis, animals are constantly readjusting physiological systems (e.g. gill ventilation rate, blood flow) which will affect unstirred layer formation. Ventilation and blood flow are influenced by many environmental factors, but the interrelationship between environmentally induced cardiovascular adjustment, unstirred layer formation, and the cost of solute transport remain to be explored. 

They observed that the emission factors for formaldehyde, benzaldehyde and possibly EMK were increased as the rabo of ventilation rate to loading ratio (product area per chamber volume) was increased. That is, the pollutant emission rates increased as the venblabon rate was increased or the loading rabo was decreased, indicabng that these pollutants were emibed at rates dependent on the pollutant concentrabons in the surrounding air. 

Viau 2005). Indeed, such factors as varying ventilation rates associated with varying workloads and dermal exposure are unaccounted for by the air measurement this might make the biomarker a better metric of the actual exposure than the air-concentration measurement of the parent chemical. 

Simple models have been developed to screen for consequences of worst-case exposures (van de Meent et al., 1995 USEPA, 1997b). For example, these models calculate worst-case exposure by dividing the amount of active ingredient by the room size. When better estimates of exposure are needed, simple models are advanced based on mechanistic processes or statistical relations, in conjunction with experiments aimed at quantifying exposnre factors (Jayjock, 1994 Matoba et al., 1998a,c van Veen, 1996) (see the model overview below). These models describe the mechanisms of exposure and inclnde key factors that influence exposure, such as ventilation rates of rooms and vapor pressures of chemicals. In addition, they provide a more precise temporal and spatial scale of exposure and dose. These scales enable identification and exposnre assessment of persons at various distances from the application and of persons having varions time-intervals of contact with the pesticide. 

The type of buildings and their construction. Factors can include, ventilation rates, resistance to blast effects, tlie ability of overhead fixtures to remain intact, etc. 

No studies were located in humans or animals regarding the absorption of inhaled 1,1-dichloroethane. However, its use as a gaseous anesthetic agent in humans provides evidence of its absorption. Furthermore, the volatile and lipophilic nature of 1,1-dichloroethane favors pulmonary absorption. Structurally related chlorinated aliphatics and gaseous anesthetics are known to be rapidly and extensively absorbed from the lung. The total amount absorbed from the lungs will be directly proportional to the concentration in inspired air, the duration of exposure, the blood/air partition coefficient of 1,1-dichloroethane, its solubility in tissues, and the individual s ventilation rate and cardiac output. One of the most important factors controlling pulmonary absorption is the blood/air partition coefficient of the chemical. The concentration of the chemical and the duration of exposure are also important determinants of the extent of systemic absorption. 

The equilibrium state of the Rn and RnD at any stage is characterized by a so-called equilibrium or F factor. An F factor of one represents a full equilibrium between Rn and RnD, while values less than one represent realistic everyday situations. The F factor in outside air is typically 0.7-0.8. In indoor environments it varies between values of 0.33 and 0.45. In underground mining situations, where the ventilation rate of the working is often very variable, the F factor varies between 0.1 and 0.7. In the former case the air is said to be young, and in the latter case the air, or Rn, is said to be old. 

The exposure concentration was converted to a human equivalent exposure concentration (853 mg/m3) by multiplying by the ratio of the alveolar ventilation rate divided by the body weight of mice to the same parameters for humans. The human equivalent concentration was divided by an uncertainty factor of 300 (10 for interspecies variability, 3 for intraspecies variability, and 10 for the use of a LOAEL) to derive the MRL. 

If the allowable concentration is specified in volume for volume units (e.g., %, ppm, ppb, etc.), then, that is used (times the appropriate factor e.g., 100, 10 , 10 , etc.) on the left-hand side. In this instance volume per unit time in the same units should be used for both of the substitutions of the right-hand side. The ventilation rate equation is also valid for use when contaminant concentration allowed is specified in mass per unit volume units such as mg/L, mg/m , p,g/m, etc. In this case, mass per unit time units are used in the numerator and volume per unit time in the denominator of Eq. 2.21. To use Eq. 2.21 in either format does not require knowledge of the volume of enclosed space being ventilated. However, it does assume perfect uniformity of the gas mixture, and perfect mixing of the air with the contaminant. 

This vapor acts as a driving force for formaldehyde diffusion from the wood cel I towards the product surface, and for emission from the finished wood product. An internal vapor pressure of 20 Torr would approximately correspond to a formaj ehyde air concentration of about 1 ppm at 25 t, a load factor of I m and a ventilation rate of 1 ach. However, as emission continues and depletes the methylene glycol concentration in the wood moisture, the dissociation of hemiacetals will set in and add to the formaldehyde source. The bottleneck in the formaldehyde transport will be diffusion through the product towards the product surface. This process depends on the permeability of the product which, in turn, depends on diffusion... 

---