Types of Air Contaminants

There are precise meanings for certain words commonly used in industrial hygiene. These must be used correctly to understand the requirements of OSHA s regulations effectively communicate with other workers in the field of industrial hygiene and intelligently prepare purchase orders to procure health services and personal protective equipment. 

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The type of air contaminants that occur in the workplace depends on the raw materials used and the processes involved. Air contaminants can be classified into two groups based on their physical properties (1) aerosols (a suspension of liquid or solid particles in the air), and (2) gases/vapors. 

The types of air contaminants have been identified, concentrations measured, and an air-purifying respirator is available that can remove the contaminants and... 

Table 21 provides a detailed logic sequence to respiratory protection for different types of air contaminants. 

Physiological Classifications of Contaminants. The physiological classification of air contaminants is difficult, because the type of action of many gases and vapors depends on concentrations (55). For example, a vapor at one concentration may exert its principal effect as an anesthetic but, at a lower concentration, the same vapor may iujure the nervous system, the hematopoietic (blood-forming) system, or some visceral organ (see Toxicology). 

Airborne contaminant movement in the building depends upon the type of heat and contaminant sources, which can be classified as (1) buoyant (e.g., heat) sources, (2) nonbuoyant (diffusion) sources, and (d) dynamic sources.- With the first type of sources, contaminants move in the space primarily due to the heat energy as buoyant plumes over the heated surfaces. The second type of sources is characterized by cimtaminant diffusion in the room in all directions due to the concentration gradient in all directions (e.g., in the case of emission from painted surfaces). The emission rare in this case is significantly affected by the intensity of the ambient air turbulence and air velocity, dhe third type of sources is characterized by contaminant movement in the space with an air jet (e.g., linear jet over the tank with a push-pull ventilation), or particle flow (e.g., from a grinding wheel). In some cases, the above factors influencing contaminant distribution in the room are combined. 

Powered air-purifying respirator (PAPR) A type of air-purifying respirator that utilizes a battery-powered fan to draw contaminated air through the cartridge or filter into the facepiece. 

A wide range of types of air cleaners is available to match the number of contaminants needing removal from air. Figure 28.5 shows typical particle size ranges and the range of operation of each type of air cleaner. 

Applicability of air-stripping methods with respect to the type of groundwater contaminants is the most important factor. The major constituents of interest, such as benzene, toluene, xylene, and ethylbenzene, are all fairly volatile and thus are easily removed by this technique. Compounds with low volatility such as 1,2-dichloroethane (DCE) cannot be readily removed. 

When designing a local exhaust ventilation system for a process that generates dust particles, it is important to consider the minimum air velocity. The minimum air velocity is the velocity required to prevent settling of dust particles in the air ducts. The minimum velocity is a function of dust particle size and particle density. Listed in the table below are the minimum air velocities recommended for the transport of various types of particulate contaminants. 

Facilities, equipment procedures and, as necessary, air-flow rates and directions, should be such as to minimize the risk of cross-contamination, although the precautions which need to be taken vary according to the type of potential contamination. 

It is unusual to think of any type of atmospheric contamination - especially by a radioactive species -as beneficial however, bomb-produced radiocarbon (and tritium) has proven to be extremely valuable to oceanographers. The majority of the atmospheric testing, in terms of number of tests and production, occurred over a short time interval, between 1958 and 1963, relative to many ocean circulation processes. This time history, coupled with the level of contamination and the fact that becomes intimately involved in the oceanic carbon cycle, allows bomb-produced radiocarbon to be valuable as a tracer for several ocean processes including biological activity, air-sea gas exchange, thermocline ventilation, upper ocean circulation, and upwelling. 

Laboratory scale" excludes those workplaces whose function is to produce commercial quantities of materials. "Laboratory-type hood" means a device located in a laboratory, enclosure on five sides with a movable sash or fixed partial enclosed on the remaining side constructed and maintained to draw air from the laboratory and to prevent or minimize the escape of air contaminants into the laboratory and allows chemical manipulations to be conducted in the enclosure without insertion of any portion of the employee s body other than hands and arms. Walk-in hoods with adjustable sashes meet the above definition provided that the sashes are adjusted during use so that the airflow and the exhaust of air contaminants are not compromised and employees do not work inside the enclosure during the release of airborne hazardous chemicals. 

A ventilation system eonsisting of mechanical air movement to mix with and dilute the eontaminants in the space and exhaust them to the outside. This is not the type of ventilation that is designed to maintain normal ventilation and thermal eomfort in a space. General ventilation is not designed to control highly toxic materials or large quantities of air contaminants. 

Lights Removal Air classification methods are used to remove light contaminants such as dust, film and foam fi agments, and paper glass powder in a recycling operation in the absence of water [1, 10]. Two common types of air classifier systems, cyclone separators and multiaspirators, are shown in Figures 14.16 and 14.17. Other types of air classifiers are air knives, elutriators, zig-zag classifiers, and air tables. Air classifiers are rather simple equipment where control is often more art than science, and the equipment must be tuned for each stream of material. Separations of materials are based on differences in terminal velocities in an airstream and are highly dependent on particle size and shape. 

Air sampling n. Determining quantities and types of atmospheric contaminants by measuring and evaluating a representative sample of air. The most numerous environmental hazards are chemical, and can be conveniently divided into (a) the particulates and (b) the gases or vapors. Particulates are mixtures or dispersions of solid or liquid particles in air and included dust, smoke, mist, and similar materials. 

Frequently exhaust vents for local exhaust systems end at building roof locations. Also on roofs there are inlets for air conditioning and recirculation systems. When inlet and exit vents are close to each other and when wind conditions are just right, exhausted contaminants may travel directly to inlets and return to the building interior. There should be adequate separation of exhaust vents both vertically and horizontally from any type of air inlet to ensure that contaminants do not reenter the building. 

Very often a local exhaust ventilation system must include a capability to remove contaminants before air moves to the outdoors. Cleaning is essential for recirculated air. There are several types of air cleaning devices. Figure 25-5 illustrates properties of aerosols and related cleaning equipment. 

Canisters or Chemical Cartridge Respirators This is one type of air-purifying respirator. Breathing air moves through a container that removes gases or vapors. No single built-in process removes all types of hazardous gases or vapors. Most canisters remove one specific gas contaminant. Some are effective only for certain concentrations of a gas. 

For most radionuclides, the inhalation dose coefficient is higher for children than for adults, but the inhalation rate (I) is probably lower for children. Therefore, the inhalation dose rates for the same level of air contamination may be even less for children and infants than for adults. The inhalation rate (I), consumption habits, and committed dose conversion coefficients with respect to groups of different ages, species of contamination in air (ionic, aerosol bound, aerosol diameter, etc.) or foodstuffs, and radionuclides are listed in tables of dose assessments (Jacob et al. 1990 IBSS 1996). These values are derived from calculations assuming various types of body phantoms and measurements. 

Ever Decent" (1999—Great Britain) Collision of a container ship witii a liner. Fire on-board tiie container ship. A number of ccmtainers of hazardous materials, especially cyanide, organic lead, and pesticides. Chemical risk from fire on board ship. Towing. Fire fighting. Control of air contamination (fear of cyanide). Difficulty in knowing the exact type of cargo. 

Some details of the hazards to be faced need to be known for example, in the case of air contaminants, the type of chemical present and its concentration, or, with noise, sound level and frequency characteristics would be needed. 

Air Sampling Refers to the collection and analysis by instrument of samples of air to detemiine the presence of hazardous materials. The reader should review Chapter 2 for the objectives and types of air sampling techniques. Air Monitoring The sampling for and measuring of contaminants in the air. 

The main sources of contamination of the food chain with mono-cycHc aromatic hydrocarbons are oil spills, but also include a variety of coatings and plastics. MonocycHc aromatic hydrocarbons may also arise as products of the combustion of various materials. Food contamination occurs primarily by absorption from the air and water, and in animals from the surrounding environment. Another type of food contamination is migration from packaging materials. In recent years, much attention has been paid to contamination of yoghurt and biscuits by styrene (vinylbenzene) released from the polystyrene used to manufacture various packagings. 

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