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Case Presentation

 

 By: Rutgers University
Why Clean Green
Case Studies
Poison Guide

Exposure Model 1: chemical composition of the mist as a function of increases in relative humidity


The specified dilution of the cleaning compound results in 37.9 mg TSP/gram of water as the 5 gallon premix solution. When further diluted by 30 additional gallons of water, the new TSP concentration is reduced to 1.26 mg TSP/gram of water as delivered to the carpet and mist released into room air. Assuming that the mist and moisture liberated into the air from the use of the cleaner results in an increase in the humidity within the room air, and that the increased airborne moisture contains dissolved TSP in the same concentrations as in the diluted cleaner, potential exposures to the victim can be projected based upon any increase in relative humidity within the home due to the release of the TSP-containing mist.

Relative humidity refers to the amount of moisture in the air as compared to the amount that the air could contain at saturation at the same temperature (10). Assuming that the temperature within the home at the start of the project was 70°F with a relative humidity of 30%, the amount of water that could be held in the air is approximately 32 grains of water per pound of dry air. If, as a result of the hot water mist liberated during the carpet-cleaning operation, the relative humidity increased to 50%, then a total of 56 grains of water per pound of dry air would be suspended. At 70% relative humidity, 76 grains/ft3 would be contained within the air, and approximately 112 grains/ft3 would be airborne at 100% relative humidity. Using the above information, the estimated exposure to TSP (in milligrams per cubic meter) can be computed by multiplying the changes in total moisture content in air from cleaning solution humidity by the room size over which the increased humidity occurs. Equations 1 and 2 display the specifics of this conversion process, using standard industrial hygiene conversion factors (5,10,11).

Total moisture grams H2O/ft3 = (grains H2O/lb air) (0.065 g H2O/grain H2O) (0.075 lb air/ft3 air) [1]

I computed an estimate of TSP exposure by multiplying the results obtained from Equation 1 (grams H2O/ft3 air) by the computed concentration of TSP per gram of water (1.26 mg TSP/gram H2O), a conversion factor of 35.31 ft3 air/m3 of air (11), and the percent of new moisture added to air as a result of the cleaning process (new moisture refers to the percentage of total moisture added by the mist liberated during cleaning).

Milligrams TSP/m3 air = (grams H2O/ft3) (1.26 mg TSP/gram H2O) (35.31 ft3/m3) (percent new moisture) [2]

Based upon the above equations, the estimate of TSP exposure is shown to increase as a function of changes in relative humidity due to the liberation of mist from the carpet-cleaning procedure, as shown in Table 1.

Table 1 shows that even a modest increase in relative humidity posed by the carpet-cleaning solution mist results in significant increases in projected homeowner inhalation exposure to TSP. This increased exposure would occur immediately at the end of the cleaning job and during the 2- to 24-hr carpet drying period that follows, until room humidity levels return to normal. The range of estimated exposure based on this approach is 5-17 mg/m3 of TSP; this is 1-3 times the recommended 15-min exposure limit for industrial workers.

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