Toxic gases models

The Toxic Gas Model Ordinance requires all Class 1 gases to be contained in a process tube enclosed in a secondary containment tube. Class 1 materials are those with a material hazard index of greater than or equal to 500,000, or that carry a US Department of Transportation classification of Poison A. (Note The Department of Transportation no longer uses the Poison A classification, and there is no direct replacement. Reference Code of Federal Regulations, Title 49, parts 172 and 173 for guidance). 

The codes and regulations governing semiconductor gas facilities include sections of the Uniform Building Code (UBC), sections of the Uniform Fire Code (UFC), the National Electrical Code (NEC), codes of the National Fire Protection Association (NFPA), and various local and state ordinances such as the Toxic Gas Model Ordinance that has been adopted in California. 

Models toxic gas releases. Two models available SHELL SPILLS and TRPUF (based on EPA PUFF). Graphical output. Requires 512K memory and 132 column printer. 

TOXIC, PUFF, SPILLS, INPUFF, AND INPUFF 2.0 Bowman Environmental Engineering P.O. Bo 29072 Dallas, TX 75229 (214) 241-1895 In ascending order of data complexity, these systems address toxic gas releases using models designed for each type of release, based on emission rate, facility characteristics and weather data. 

TRACE II Toxic Release Analysis of Chemical Emissions Safer Emergency Systems, Inc. Darlene Davis Dave Dillehay 756 Lakefield Road Westlake Villa, CA 91361 (818) 707-2777 Models toxic gas and flammable vapor cloud dispersion. Intended for risk assessment and planning purposes, rather than realtime emergencies. 

VDI Part 1 models the dispersion of vapor plumes with output consisting of vapor ctiriccntration as a function of time and downwind distance and denser-than-air vapor releases. VDI Part 2 determines the downwind distance to the lower flammable limit of a combustible vapor. Part 2 may also be used in conjunction with Part 1 to model a toxic gas emission. 

Effect models describe the impact of the physical effects of a fire, e.xplosion, or toxic gas release on exposed people, the environment or property, based on the results of tlie source, dispersion, and fire and explosion models. 

Hydrogen sulfide is a toxic gas with the foul odor of rotten eggs. The Lewis structure of H2 S shows two bonds and two lone pairs on the S atom. Experiments show that hydrogen sulfide has a bond angle of 92.1°. We can describe the bonding of H2 S by applying the orbital overlap model. 

The analysis of the potential consequences of an accident is a useful way of understanding the relative inherent safety of process alternatives. These consequences might consider, for example, the distance to a benchmark level of damage resulting from a fire, explosion, or toxic material release. Accident consequence analysis is of particular value in understanding the benefits of minimization, moderation, and limitation of effects. This discussion includes several examples of the use of potential accident consequence analysis as a way of measuring inherent safety, such as the BLEVE and toxic gas plume model results shown in Figures 4, 5, and 6. 

Tietge, J.E., Mount, D.R. and Gulley, D.D. (1994) The Gas Research Institute freshwater salinity toxicity relationship model and computer program overview, validation and application, Topical Report, Gas Research Institute, Chicago, IL, USA. 

Researchers at the NIST developed a concept to minimize the usage of animals for the assessment of the toxic potency of a material in fires. This concept is based on the well-established hypothesis that a small number (N) of gases in the smoke accounts for a large percentage of the observed toxic potency. Research at NIST of toxicologically important gases and their interactions resulted in the development of the /V-Gas Model,65 which is expressed by the following equation ... 

Both equations have been taken from ISO 1334431 and use LC50 values for lethality to provide reference data for the individual gases to calculate toxic potency, based on rats exposed for 30 min. The N-Gas model in Equation 17.1 assumes that only the effect of the main toxicant CO is enhanced by the increase in respiration rate caused by high C02 concentrations (expressed as a step function with one value of m and b for C02 concentrations below and another for those above 5%). 

Instead of normalizing the data to an arbitrary 1 g in 200 L, the fire toxicity of a material can be expressed as an LC50, which in this case is the specimen mass M of a burning polymeric material, which would yield an FED equal to one within a volume of 1 m3. The relation to the FED from the N-Gas model is given in Equation 17.6. 

B.C. Levin, New research avenues in toxicology 7-gas N-gas model, toxicant suppressants, and genetic toxicology, Toxicology, 115, 89-106, 1996. 

Harris, N. C. 1991. Containment Building and Scrubber for Toxic Gas Plants. Proceedings of the International Conference and Workshop on Modeling and Mitigating the Consequences of Accidental Releases of Hazardous Materials, pp. 443-452. New York American Institute of Chemical Engineers. 

Buckley, R.L., Hunter, C.H., Addis, R.P., Parker, M.J. (2007). Modeling dispersion from toxic gas released after a train collision in Qraniteville, SC. J. Air Waste Manage. Assoc. 57(3) 268-78. 

The N-gas models for predicting smoke toxicity were founded on the hypothesis that a small number N)... 

The modeling of a vapor cloud following a release requires the use of highly specialized mathematical models, most of which are based on the Gaussian model, which assumes that the released gas has a normal probability distribution. Generally, the output from one of these models has a cigar shape, such as that shown in Figure 14.4, which is an elevation view for the release of the toxic gas H2S. 

Your task as a design engineer in a chemical company is to model a fixed bed reactor packed with the company proprietary catalyst of spherical shape. The catalyst is specific for the removal of a toxic gas at very low concentration in air, and the iifformation provided from the catalytic division is that the reaction is first order with respect to the toxic gas concentration. The reaction rate has units of moles of toxic gas removed per mass of catalyst per time. 

As a design engineer, you are asked by your boss to design a wetted wall tower to reduce a toxic gas in an air stream down to some acceptable level. At your disposal are two solvents, which you can use in the tower one is nonreactive with the toxic gas but is cheap, whereas the other is reactive and quite expensive. In order to choose which solvent to use, you will need to analyze a model to describe the absorption of the toxic gas into the flowing solvent (see Fig. 10.16). 

The determination of toxic release consequences consists from modelling release, dispersion, exposure and effects of toxic gas. The consequences are quantified as ... 

A case study is performed assuming an instantaneous release of the toxic liquid acrylonitrile from a rail tankwagon. After the release of the toxic liquid a pool of 600m is formed from which evaporation occurs, leading to a vapour cloud. This vapour cloud travels with the wind and disperses. The degree of dispersion is determined by the wind speed, the stability of the atmosphere and the surface roughness. The stability of the atmosphere is indicated by the pasquill-stabUity class. By day, the most common atmospheric stability class is class D and a wind speed of 5 m/s is assumed, this weather condition is abbreviated with D5. At night class F is the most common atmospheric stability, associated with a wind speed of 1.5 m/s this weather condition is abbreviated as FI.5. The evaporation and dispersion calculations are performed with EFFECTS 7.6. A neutral gas model is used for the dispersion calculations. 

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