Airborne toxic material

Modeling of Human Exposure to Airborne Toxic Materials... 

For environmental control of airborne toxic material the most common method of choice is ventilation, for the following reasons ... 

Dispersion models describe the airborne transport of toxic materials away from the accident site and into the plant and community. After a release the airborne toxic material is carried away by the wind in a characteristic plume, as shown in Figure 5-1, or a puff, as shown in Figure 5-2. The maximum concentration of toxic material occurs at the release point (which may not be at ground level). Concentrations downwind are less, because of turbulent mixing and dispersion of the toxic substance with air. 

A system of guidelines for air concentrations of toxic materials prepared by the American Industrial Hygiene Association. An ERPG is the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour with the following results ... 

The acceptable limits for toxic exposure depend on whether the exposure is brief or prolonged. Lethal concentration for airborne materials and lethal dose for non-airbome materials are measured by tests on animals. The limits for brief exposure to toxic materials that are airborne are usually measured by the concentration of toxicant that is lethal to 50% of the test group over a given... 

SRM 1649 was originally collected in a bag house over a period of one year in the late 1970s at a site near Washington, DC, screened through a 200-mesh sieve (cutoff point 125 gm), and since then apparently stored in bottles at room temperature (Lewtas et al., 1990a). Understandably, Claxton et al. (1992a) caution While the air particles in SRM 1649 are similar to other air particulate samples, they do not represent a typical air particulate sample as collected by most researchers—they are intended as reference materials and not as samples for assessment of levels of airborne toxicants. ... 

Figure 3 shows data for a spinner atomizer in a 110 mi/hr airstream. The vmd is 140 microns, the % volume in drops less than 122 microns is now 24% while the relative span has increased to 1.23. It is this tremendous increase of drops (less than 122 microns dia.) from 2.0% for the 300 microns spray to 24% for the 150 microns spray that is a potential source of trouble from airborne transport of these small drops. These are carried away from the treatment area and a potential exists for contact with humans and animals as well as unwanted deposit on non-target crops. These small drops have been found at distances of several miles from the actual applications (5). If the material being released is of low toxicity, or in a remote area, the problem is not serious. But for high toxicity materials the 24% loss which is not controlled, poses a serious problem. 

Toxic cloud Airborne plume of gases, vapors, fumes, or aerosols containing toxic materials. 

When a flammable or toxic material is released, all the potential hazards, except for pool and jet fires, are associated with airborne concentrations of the material. The material is either released as a vapor, subsequently vaporizes from a pool of spilled material, or is entrained as an aerosol during the release and subsequently vaporizes. This section considers methods for suppressing aerosol entrainment and evaporation. 

The effects of the release of a toxic material are proportional to both its airborne concentration and the duration of the release that is, the greater the concentration or time of exposure, the greater the consequences to those who are exposed. The toxic effect can be expressed mathematically in a probit equation that calculates the probability of damage, Y (CCPS, 1989a). The equation is... 

Using dry powders for the mitigation of airborne or liquid HF and other toxic materials is possible. The technique would work well where the maximum spill is known in advance so that stationary dry powder systems of finite, yet sufficient, capacity could be designed. 

Insofar as mercury and cadmium are concerned, and lead to a lesser extent, no matter how the incinerators are operated, a significant fraction of these materials will be volatilized during incineration and enter the ecosystem via the airborne path, unless recovered from the flues by fly ash precipitation and vapor condensation, methods of questionable merit for large scale MSW operations, uie remainder of the cadmium and lead will end up in the incinerator ash and in the incinerator residues, but all the mercury may be expected to be volatilized. This means that unless the reduction of the toxic materials at the source can be practiced, the incinerator residues and flues will need to be processed to remove lead and cadmium for recycling or for safe disposal in some other manner. The most effective and also the most economical way to prevent mercury from entering the environment from batteries is to phase out the use of mercury in batteries to the ftillest extent possible, an effort already instituted by the battery manufacturers, and to maintain an effective collection system for the mercury batteries still in use. 

Airborne (and consequently inhaled) toxic material may be encountered in gaseous or particulate form (Exhibit 9-1). Airway distribution of toxic... 

In a situation where the only problem is the generation ofairborne radioactivity, individuals should leave the space in which the airborne activity is present,closing the doors behind them and turning off any ventilation in the area, if the controls are in the room. If the ventilation controls are inaswitchroomorbreakerroomelsewhere, they can be turned off from this location. If the accident occurs in or near a fume hood that would vent the material from the laboratory, it may be appropriate to allow the hood to remain on to reduce the airborne concentration of activity within the room however, this would depend uponthe radioactive toxicity ofthe material involved. If it is one ofthe more toxic materials,it would usually be preferable to avoid dispersal into a public area even if the levels are low, because of the possible concerns of exposure to persons in theseareas.Even ifthe potential forexposure is minuscule,many persons will become very alarmed. The laboratory represents a controlled space that can be decontaminated and, in general, the best approach is to restrict the contaminated area as much as possible. 

Fire (radiological and toxic material) Forklift fire incident causes transfer cask breach with possible target exposure and airborne release Failure of electrical equipment or system in SCBs, SGB, ventilation hood, Zone 2 or Zone 2A canyon Lightning strike External fire (vehicle accident, aircraft crash, other building fire) irradiated isotope production target, up to 20,000 curies. Volatiles in process cold traps, up to 70,000 curies. Same material as toxic spill. Residual radiological contamination. 

Fire (radiological and toxic material) Forklift fire incident causes transfer cask breach with possible target exposure and airborne release (TT-4 CP-1) IV D 4... 

Respiratory protection is the most critical aspect of all protective clothing. The most common exposure route is the respiratory system. Most chemical agents are dispersed as an aerosol vapor or, in the case of biological or radiological agents, as small particles suspended in an aerosol. The atmosphere at explosion scenes will be very dusty (fine airborne particles). Working at an explosion scene requires respiratory protection, as this dust may contain asbestos or other toxic materials. 

Generic Safety Issue (GSI) 083 in NUREG-0933 (Reference 1), deals with ensuring that the control room design is adequate to preclude the loss of control room habitability following an accidental release of external airborne toxic or radioactive material or smoke which could impair the control room operators ability to safely control the reactor. 

No new design requirements were established by the NRC as a result of this and other work related to control room habitability in an accident. However, more specific review procedures were incorporated in SRP Sections 6.4.1 and 9.4.1 (Reference 2), including the habitability review provisions of TMI Action Plan Item III.D.3.4 (Reference 1) regarding analyses of toxic gas concentrations and operator exposures from airborne radioactive material and direct radiation, to ensure more effective implementation of existing requirements. 

The sample container must be clean, dry and airtight. Its function is not only to protect the sample from contamination by extraneous matter such as atmospheric moisture and carbon dioxide or airborne particulate materials, but also to prevent changes in composition through loss of volatile components, and the escape of toxic or flammable vapours. It should be filled as full as possible, leaving minimal head-space, and the closure must be put on securely. 

The range and diversity of toxic materials used in process industries are large, but common toxic and volatile chemicals include, e.g., chlorine, bromine and phosgene. Large release of any of these could present lethal risk many kilometers downwind. The hazard arising from toxic releases is a function of the chemical s toxicity (obviously), the discharge rate (which will affect airborne concentration), the chemical volatility, whether Are or other heat source are present (since this may induce buoyancy and reduce ground-level concentrations), local population density, and local weather at the time of the release. 

Accumulated toxic materials may become suspended in air, and may contribute to airborne exposures (e.g., asbestos, lead or beryllium). Bulk and wipe samples may aid in determining this possibility. 

Inhalation involves those airborne contaminants that can be inhaled directly into the lungs and can be physically classified as gases, vapors, and particulate matter that includes dusts, fumes, smokes, and mists. Inhalation, as a route of entry, is particularly important because of the rapidity with which a toxic material can be absorbed in the lungs, pass into the bloodstream, and reach the brain. Inhalation is the major route of entry for many hazardous chemicals in the work environment. 

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