Dietrich A. Weyel

Sensory and pulmonary irritation with exposure to methyl isocyanate

Methyl isocyanate (MIC) was tested for its potency as a sensory irritant and as a pulmonary irritant in mice. To evaluate sensory irritation, animals were exposed to MIC at concentrations between 0.5 and 7.6 ppm for a period of 90 min. A characteristic reflex decrease in respiratory rate indicating sensory irritation was observed. The concentration evoking a 50% decrease in respiratory rate (RD50) was found to be 1.3 ppm. To evaluate pulmonary irritation, animals were first anesthetized and fitted with a tracheal cannula. Following recovery from anesthesia, they were exposed to MIC at concentrations between 0.4 and 7.3 ppm for a period of 90 min. A characteristic decrease in respiratory rate indicating pulmonary irritation in tracheally cannulated (TC) mice was observed. The concentration evoking a 50% decrease in respiratory rate (RD50TC) was found to be 1.9 ppm. Thus, MIC was found to be a potent sensory and pulmonary irritant.

Pulmonary reactions to inhaled cotton dust: An animal model for byssinosis☆

Groups of guinea pigs were exposed to respirable particles of cotton dust obtained from opening and carding rooms of a textile mill. The bulk cotton dust was resuspended with a modified sonic sifter. Exposures were conducted 6 hr/day at concentrations varying between 16 and 25 mg/m3. The particle size for these exposures varied around a 3 micron aerodynamic equivalent diameter. In animals exposed for 5 days, a pulmonary effect began to develop 3 hr after the start of exposure on the first day and was maximal 18 hr postexposure. The pulmonary effect faded during the ensuing weekdays as daily exposures continued. In one group exposed for 6 weeks, 5 days/week, the pulmonary effect was apparent on each Monday and faded during the week. The pulmonary response can best be characterized as a reflex restriction of breathing from stimulation of vagal nerve endings, resulting in rapid shallow breathing. This effect was exaggerated upon challenge of the animals with air containing 10% CO2. In humans this pattern of rapid shallow breathing is associated with symptoms of shortness of breath, dyspnea, breathlessness, and fatigue upon exertion. Such symptoms are characteristic of those reported by workers exposed to cotton dust. This animal model is proposed for further evaluation of the possible relationship between the acute responses to cotton dust and the development of a chronic response.

Sensory irritation, pulmonary irritation, and acute lethality of a polymeric isocyanate and sensory irritation of 2,6-toluene diisocyanate

Abstract The use of monomeric and polymeric isocyanates in a wide variety of industries has been increasing. Little is known about the toxicity of polymeric isocyanates and the widely used 2,6-toluene diisocyanate (TDI) isomer. The pulmonary and sensory irritation of an aliphatic polyisocyanate (DES-N) based on hexamethylene diisocyanate (HDI) was studied in Swiss-Webster male mice during aerosol exposures in the range of 25 to 131 mg/m 3 . The sensory irritation of 2,6-TDI vapor was studied in the range of 0.37 to 7.6 mg/m 3 (0.05 to 1.1 ppm). The aerodynamic equivalent diameter and geometric standard deviation for the DES-N aerosol were 0.6 μm and 2.4, respectively. High-speed liquid chromatography was used to determine both free HDI in DES-N and HDI in the exposure chamber. Each exposure was for 3 hr during which the tidal volume pattern and respiratory rate of groups of four mice were recorded. Unlike the monomeric isocyanates, DES-N acted predominantly as a pulmonary irritant, evoking little sensory irritation. The concentration needed to reduce the respiratory rate 50% due to pulmonary irritation was 57.1 mg/m 3 . The LC50, determined by counting the number of deaths within the 24 hr period following a 4-hr exposure, was 91.2 mg/m 3 . In groups of animals killed 2 hr after the 4-hr exposure, the concentration of DES-N needed to increase lung weight by 50% was 45 mg/m 3 . Based on comparisons with another pulmonary irritant, nitrogen dioxide, the maximum concentration for DES-N permitted in industry should be 1 mg/m 3 with a time-weighted average for an 8-hr period of 0.5 mg/m 3 . From the concentration-response relationship due to sensory irritation for 2,6-TDI, the RD50 was determined to be 1.8 mg/m 3 (0.26 ppm) which is close to the value of 1.4 mg/m 3 (0.20 ppm) determined previously for 2,4-TDI. No pulmonary irritation was observed. For industrial applications the exposure limit for 2,4-TDI of 0.04 mg/m 3 (0.006 ppm) is also suggested as appropriate for the 2,6-TDI isomer.

An aerosol generator for the resuspension of cotton dust.

An aerosol generator, the Pitt 3 model, was designed, fabricated, and characterized for the resuspension of inhalable particles from bulk cotton dust. The generator was constructed around a loudspeaker whose energy is transferred into an air column through latex rubber dams. This action tumbles the bulk dust, and small particles are loosened which can then be carried out of the column with the air passing through it. Thirty to forty grams of bulk cotton dust produced a stable aerosol concentration for at least 90 min. The maximum output of about 100 mg/m3 can be reduced to lower concentrations by adding dilution air. In one application, the generator produced a stable aerosol cloud in the range of 2 to 30 mg/m3 with a mass median aerodynamic diameter (MMAD) of about 3 microns and a geometric standard deviation (sigma g) of about 1.5. In another application the concentration in an animal exposure chamber was kept at 20.8 mg/m3 with an MMAD = 2.5 microns and a sigma g = 1.8 for over 6 months. The Pitt 3 generator proved to be trouble-free and produced large amounts of inhalable particles from bulk cotton dust. The generator was also used to generate dust clouds from silica powder, fly ash, and cellulose dust. The only requirement for successful resuspension of any dust with this generator is the presence of small particles in the bulk feed dust.

Assessment of the Cough Reflex Caused by Inhalation of Sodium Lauryl Sulfate and Citric Acid Aerosols

Guinea pigs were exposed for thirty minutes to a particulate aerosol of sodium lauryl sulfate at concentrations of 17.3, 28.9 and 48.6 mg/m3. The exposure chamber in which individual guinea pigs were exposed was fitted with a microphone to record coughing. As the concentration of sodium lauryl sulfate increased, the combined number and severity of the coughs increased and a fade in the response was also observed with exposure duration. Citric acid, a tussigenic agent commonly used to test antitussive agents was also tested using the same experimental protocol and was found to be about an order of magnitude less potent than sodium lauryl sulfate. This model could be useful in assessing the irritating properties of various aerosols to the tracheo-bronchial tree.

Concentration-dependent respiratory response of guinea pigs to a single exposure of cotton dust

Eight groups of guinea pigs were exposed to cotton dust at concentrations of 2 to 27 mg/m3. Each exposure was for 6 hr. The pulmonary function of each animal was assessed prior to exposure, following exposure, and 18 hr following exposure. Tidal volume decreased while respiratory frequency increased in a concentration-dependent manner. These changes were amplified when the same measurements were conducted while the animals were breathing an atmosphere containing 10% CO2 in 19% O2 and 71% N2. Greatest response was noted at 18 hr postexposure. The concentration-response effects can be applied to evaluate the respiratory potencies of different cotton dusts grown under a variety of conditions.

A note on the penetration of a circular tube by an aerosol with a log-normal size distribution

Abstract The equation of Gormley and Kennedy is used to calculate the penetration of log-normally distributed aerosols through circular tubes. Computer solutions are presented for aerosols of geometric mean radius from 10−7 to 10−5 cm and with standard geometric deviations of 1·00, 1·59, 2·00 and 2·51.

Aerodynamic properties of exhaust hoods

State of the art hood design supposes that the required rates of exhaust can be calculated using a simple centerline formula. A design based on this simplification carries the possibilities of poor capture efficiency or aerodynamic efficiency. In this paper, the theoretical and experimental determination of three dimensional velocity contours for right quadrilateral exhaust hoods is reported. The results show that the theoretical equation can be used effectively to quantitate the three dimensional velocity contours, thus opening possibilities for optimization of hood design with respect to both capture and aerodynamic efficiencies.

Design and Calibration of a Low Flow Parallel Stage Impactor

A low flow, compact Parallel Stage Impactor was designed, constructed and calibrated. This instrument has six stages: one for total collection of air particulates, and the other five with cut-off sizes of 0.34 micrograms, 0.75 micrograms, 1.90 micrograms, 3.12 micrograms and 7.43 micrograms aerodynamic equivalent diameter. Flow through the individual stages is controlled by adjustable needle valves, which act as critical orifices. Flow was 700 mL/min per stage, resulting in a total flow of 4.2 L/min. The instrument was calibrated using uranine test aerosols, photofluorescence and optical microscopy techniques. There was excellent agreement between theoretical calculations and observed performance. The instrument design details and performance suggest a rugged and reliable field instrument for particle size analysis.

Pressure Drop in Elbows

Abstract The flow of air through elbows and the attendant pressure drop is an integral part of the design of a ventilation system. The traditionally used constants which express such a pressure drop as a function of sharpness of turn and the values of such constants in widely used references were found not to be representative of the experimental values obtained. From the experiments carried out using a wide range of elbows, the results obtained suggest that a single semi-empirical equation may be used to describe pressure drop through elbows of different duct surface characteristics, diameters, and turning ratios. The results obtained for ducts of circular cross section and the resulting equations may be readily used in the design of industrial ventilation systems.