The effects of temperature and pressure on airborne exposure concentrations when performing compliance evaluations using ACGIH TLVs and OSHA PELs.

Occupational hygienists perform air sampling to characterize airborne contaminant emissions, assess occupational exposures, and establish allowable workplace airborne exposure concentrations. To perform these air sampling applications, occupational hygienists often compare an airborne exposure concentration to a corresponding American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) or an Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL). To perform such comparisons, one must understand the physiological assumptions used to establish these occupational exposure limits, the relationship between a workplace airborne exposure concentration and its associated TLV or PEL, and the effect of temperature and pressure on the performance of an accurate compliance evaluation. This article illustrates the correct procedure for performing compliance evaluations using airborne exposure concentrations expressed in both parts per million and milligrams per cubic meter. In so doing, a brief discussion is given on the physiological assumptions used to establish TLVs and PELs. It is further shown how an accurate compliance evaluation is fundamentally based on comparison of a measured work site exposure dose (derived from the sampling site exposure concentration estimate) to an estimated acceptable exposure dose (derived from the occupational exposure limit concentration). In addition, this article correctly illustrates the effect that atmospheric temperature and pressure have on airborne exposure concentrations and the eventual performance of a compliance evaluation. This article also reveals that under fairly moderate conditions of temperature and pressure, 30 degrees C and 670 torr, a misunderstanding of how varying atmospheric conditions affect concentration values can lead to a 15 percent error in assessing compliance.

The effect of thermal loading on laboratory fume hood performance.

A modified version of the ANSI/ASHRAE 110-1995 Method of Testing Performance of Laboratory Fume Hoods was used to evaluate the relationship between thermal loading in a laboratory fume hood and subsequent tracer gas leakage. Three types of laboratory burners were used, alone and in combination, to thermally challenge the hood. Heat output from burners was measured in BTU/hr, which was based on the fuel heat capacity and flow rate. Hood leakage was measured between 2824 and 69,342 BTU/hr. Sulfur hexafluoride (SF6) was released at 23.5 LPM for each level of thermal loading. Duct temperature was also measured during the heating process. Results indicate a linear relationship for both BTU/hr vs. hood leakage and duct temperature vs. hood leakage. Under these test conditions, each increase of 10,000 BTU/hr resulted in an additional 4 ppm SF6 in the manikin's breathing zone (r2 = 0.68). An additional 3.1 ppm SF6 was measured for every 25 degrees F increase in duct temperature (r2 = 0.60). Both BTU/hr and duct temperature models showed p < 0.001. For these tests, BTU/hr was a better predictor of hood leakage than duct temperature. The results of this study indicate that heat output may compromise fume hood performance. This finding is consistent with those of previous studies.

Exposure at home to airborne concentrations of nitrogen mustard during topical application for the treatment of mycosis fungoides: a case study.

BACKGROUND: Although effective at treating mycosis fungoides (MF), nitrogen mustard (HN(2)) creates potential exposure risks to those who administer it, including health care workers and family members. OBJECTIVE: The main objective was to examine the potential for nontarget individuals to be exposed to HN(2) vapors during and shortly after treatment with HN(2) in a home environment. METHODS: Air concentrations of HN(2) were measured during the topical treatment of MF in a patients home. RESULTS: The results demonstrate that eye and mucous membrane irritation may occur at HN(2) levels commonly encountered during the treatment of MF in the home, hospital or health clinic. Because no exposure thresholds have been developed for HN(2), the exposure thresholds of a surrogate chemical (sulfur mustard) were used. CONCLUSIONS: The study findings show that eye and mucous membrane irritation may occur at HN(2) levels below the exposure thresholds of the surrogate chemical. Recommendations for controlling exposures to HN(2) in the home are given.

Evaluation of nongermicidal handwashing protocols for removal of transient microbial flora.

A method has been described which can compare the efficacy of different nongermicidal handwashing protocols for removal of transient microbial flora without the necessity of establishing or relying on a previously determined baseline for an individual subject. The wash effluent is collected, and colony counts for the effluent reflect the number removed by the wash protocol. A second standard wash in a handwashing machine is performed, and the test criterion is the percent removed in the test wash based on the sum of total CFU recovered from the two washes. The method was used to compare an 8-s cycle for a newly developed handwashing machine with a conventional 15-s Ivory soap wash. When machine pressure was adequate (42 lb/in2), there was no statistically significant difference in the percent removal of transient flora by the two methods (48.8% from the machine versus 45.1% from the Ivory soap wash). At 32 lb/in2, the Ivory soap wash recovered 60.3%, whereas the machine recovered 45.1%.