Modeling the size of small spills of pure volatile liquids for use in evaporation rate and air concentration modeling.

Exposure modeling is a valuable tool for assessing chemical vapor exposures that occur during transient events such as small spills of volatile liquids. Models are available to estimate liquid evaporation rates and resulting air concentrations. However, liquid evaporation rate models require the surface area of the puddle in order to provide vapor generation rates in terms of mass per time. This study developed an approach to model the surface area of small spills of pure liquids. A theoretical equation exists relating puddle depth to a liquid's surface tension, density, and contact angle. A contact angle is a characteristic of liquid-solid interactions at the edge of a puddle. If the depth of a puddle can be calculated and the volume of the liquid spilled is known, the surface area of the puddle can be determined. Values for density and surface tension are published. Contact angles, however, are not readily available. Five hundred and eighty experimental spills were conducted using acetone, ethanol and water. The effective contact angle for each spill was determined. Spill volumes varied from 1.0-30.0 mL. The height of the liquid release varied from 0-15 cm onto a variety of surfaces. The effective contact angle of a puddle was most strongly associated with the liquid's polarity. The height of the liquid release and type of surface had significant, but smaller effects on the puddle size. The effective contact angle of a puddle from a spill can be estimated as ln(Ï´eff) = 3.73 - 1.17 · 1χυ/f - 0.06 · h + S. In this equation, 1χυ/f is the polarity index of the liquid, h is the height of liquid release (cm), and S is a surface constant. Ï´eff can be used with the liquid density, surface tension and volume to calculate the surface area of the puddle. The surface area of the puddle can then be used in evaporation rate models to determine a vapor generation rate for input to vapor concentration models.

Interzonal airflow rates for use in near-field far-field workplace concentration modeling.

Interzonal air flow rates (ß) for a workspace above a table were measured in 12 indoor air spaces using an experimental apparatus simulating a vapor release into an occupied near zone. The near field was modeled as a 0.32 m3 rectangular cube volume 0.60 m high above the 0.60 m × 0.90 m table. A total of 74 experimental measurements of ß were made. The apparatus consisted of photoionization detectors measuring concentrations of acetone around an evaporating liquid surface with a robot arm simulating worker motion in the near field. The vapor release rate and the resulting concentrations were used in a near-field far-field (NF-FF) model to calculate ß. Measures of mixing within the near-field supported the assumption of the NF-FF model that the near field is well-mixed. Measured values of ß ranged from 0.4-19 m3/min with an average of 4.8 m3/min. This corresponds to 1.2-59 air changes per minute in the near field and an average of 15 air changes per minute. The values of ß were log normally distributed with a geometric mean of 3.4 m3/min and a geometric standard deviation of 2.3. The 95% confidence interval on the geometric mean of ß was 2.8-4.2 m3/min. The product of the random air speed in the room and one half of the near-field free surface area was shown to be a good method of determining ß. There was a slight correlation seen between room volume and ß, but the effect size was small. Room air change rate was not found to be correlated with ß. The observed distribution of ß will be helpful in selecting values for interzonal airflow rate in NF-FF modeling of worker exposures.

Mass balance source apportionment modeling of indoor air pollution exposures during the Ethiopian coffee ceremony.

Mass balance modeling was used to apportion previously measured carbon monoxide and respirable particle exposures of women preparing coffee during Ethiopian coffee ceremonies. The coffee ceremony generates smoke indoors from the use of charcoal and incense. This creates inhalation exposures, particularly for the women preparing the coffee. Understanding the health risks associated with this practice will be improved with knowledge of the relative contribution to combustion byproduct exposures from the different sources. Source fingerprints were developed in the laboratory for carbon monoxide and respirable particle emissions from charcoal and incense. A mass balance model determined that the majority of the carbon monoxide exposures were from charcoal use and that the respirable particle exposures were approximately half from incense and half from charcoal. Efforts to decrease health risks from these exposures must be directed by Ethiopian cultural stakeholders who understand the exposure conditions, the health risks, and the societal context.

Inhalation exposures to particulate matter and carbon monoxide during Ethiopian coffee ceremonies in Addis Ababa: a pilot study.

The unique Ethiopian cultural tradition of the coffee ceremony increases inhalation exposures to combustion byproducts. This pilot study evaluated exposures to particulate matter and carbon monoxide in ten Addis Ababa homes during coffee ceremonies. For coffee preparers the geometric mean (57 µg/m³) and median (72 µg/m³) contributions to an increase in a 24-hour time-weighted average exposure were above World Health Organization (WHO) guidelines. At 40% of the study sites the contribution to the 24-hour average exposure was greater than twice the WHO guideline. Similar exposure increases existed for ceremony participants. Particulate matter concentrations may be related to the use of incense during the ceremony. In nearly all homes the WHO guideline for a 60-minute exposure to carbon monoxide was exceeded. Finding control measures to reduce these exposures will be challenging due to the deeply engrained nature of this cultural practice and the lack of availability of alternative fuels.

An application of exposure modeling in exposure assessments for a university chemistry teaching laboratory.

Chemical exposures in a university teaching lab were assessed using a tiered approach to modeling. Zero ventilation and well mixed room models estimated air concentrations of ethyl ether, n-hexane, and methylene chloride during distillation and extraction exercises. A simple, zero ventilation model determined that health risks from the ethyl ether exercise were minimum. N-hexane and methylene chloride exposures were evaluated with higher tiered, well mixed room models. An assumption that all of the solvent evaporated during the lab resulted in estimated n-hexane concentrations well below the occupational exposure limit. Methylene chloride concentration estimates using this approach were only one-half the occupational exposure limit, so the model was refined using information on the actual amount of solvent that evaporated. This resulted in a concentration estimate approximately one-fifth of the occupational exposure limit. Air sampling was done to evaluate model performance. Measured concentrations were higher than modeled concentrations by up to a factor of two but were still below applicable occupational exposure limits. The exposure models selected were deemed useful in the assessment of exposure acceptability in these labs.