Airborne contamination ventilation

In recent years, the use of solvent-borne adhesives has been seriously restricted. Solvents are, in general, volatile, flammable and toxic. Further, solvent may react with other airborne contaminants contributing to smog formation and workplace exposure. These arguments have limited the use of solvent-bome adhesives by different national and European regulations. Although solvent recovery systems and afterburners can be effectively attached to ventilation equipment, many factories are switching to the use of water-borne rubber adhesives, hot melts or 100% solids reactive systems, often at the expense of product performance or labour efficiency. 

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. 

Brief description of ventilation systems. More details should be given for critical areas with potential risks of airborne contamination (schematic drawings of the systems are desirable). Classification of the rooms used for the manufacture of sterile products should be mentioned. 

The objective of ventilation is to ensure an adequate supply of fresh air at the workplace along with removal of airborne contaminants. There are two basic types of ventilation dilution ventilation, or general ventilation, and exhaust ventilation, or local ventilation. 

Ljungvist, B., and Reinmueller, B. (1995), Ventilation and Airborne Contamination in Clean Rooms, Pharmacia A/B, Stockholm. 

Ventilation is an important method of reducing the level of toxic airborne contaminants in the process environment. Ventilation includes general (dilution) ventilation and local exhaust (vent) ventilation. General ventilation involves dilution of air and hence the term dilution ventilation. Local exhaust ventilation is a method of removing contaminants before they enter the workplace air. Local ventilation is typically achieved by employing a hood that covers the specific area of contamination. 

Removal of particles from an indoor environment by ventilation and filtration. As a result of the operation of natural or mechanical ventilation systems particles generated indoors are removed from indoor environments, but at the same time particles from outdoors penetrate indoors. Filers remove a certain fraction of particles from the air supplied indoors. Ventilation and air filtration are the main remedial actions available to reduce the concentration of airborne contaminants indoors. The design and operation of the filtration and ventilation systems and the type of filters used are of critical importance. 

Airborne contaminants should be controlled through effective ventilation. 

Letz GA Sick building syndrome acute illness among office workers—the role of building ventilation, airborne contaminants and work stress. Allergy Proceedings 11 109-116,1990... 

Contamination may arise from use of solvents within the laboratory or from an adjacent laboratory with a shared ventilation system and can lead to airborne contamination of sample vials and other equipment. Particular care should be taken in the area where samples are handled and transferred and during the preparation of concentrated standard solutions. Many laboratories, particularly where large volumes of solvents are regularly used, find it necessary to have special room, often positively pressurised, for the preparation and analysis of samples for VOCs. Recently decorated rooms can also be a source of VOCs from surface coatings. Contamination can often be intermittent with the wind direction being the controlling factor. 

Ventilation systems—consist of air handling and vent hoods, air movers, and positive pressure environments. Ventilation is used for control of airborne contaminants. Both local exhaust ventilation and general exhaust ventilation are used. Local ventilation is more desirable because it follows the rule... 

Additionally, to limit the buildup of contamination in the above designated areas, airflow is established to continually remove airborne contaminants. Airflows in the system are established at prescribed flowrates such that they are adequately filtered prior to being discharged to the environment. All air drawn from Zone 1 is exhausted through charcoal and HEPA filters to remove halogens and particulate contaminants from the exhaust air prior to release to the atmosphere. These ventilation filter systems are equipped with test ports and are periodically checked for operating efficiency. In addition to the ventilation system filters, in-box filtere are used to reduce the levels of airborne contaminants that are drawn into the Zone 1 ducting. 

In the MER, a separate fan exhausts 400 cfm from the Zone 1 Filter Room and discharges it into the ventilation exhaust. The purpose of this system is to exhaust any airborne contamination that could result from Zone 1 ventilation system filter replacements or fan maintenance to the HCF stack. 

The residual inventory in Zone 2A outside of the SCBs is represented by an airborne concentration of 51 microcuries of iodine, which is the only specie with significant volatility. This inventory level represents a decontamination factor of 10,000 relative to the average contamination levels in the SCBs during processing operations, which should be readily achievable given that proper airflows are maintained in the HCF. Normal ventilation system operation will continuously sweep out airborne materials, and will provide airflow across surfaces that would tend to pick up any readily volatized material. It is likely that the airborne contamination levels will be much lower than that assumed here and that any residual contamination on Zone 2A surfaces would likely remain in place following a DBE. 

Equation (10-7) is the continuity equation. Sometimes there are correction factors added to Equation (10-7) for flow through orifices of various shapes. Chapter 25 has an example applying the continuity equation for ventilation of airborne contaminants. 

Ventilation Ventilation is useful for airborne contaminants. There are two types of ventilation for controlling hazardous substances. One type of ventilation is general ventilation. The second type is local exhaust ventilation. Chapter 25 gives details on ventilation. 

What are the two major types of ventilation for controlling airborne contaminants ... 

Adequate ventilation (natural, mechanical, or respiratory) must be provided for all welding, cutting, brazing, and related operations. Adequate ventilation means enough ventilation so that a person s exposure to hazardous concentrations of airborne contaminants is maintained below the level set by federal standards. 

Health and Safety Executive (2011) Controlling airborne contaminants at work. A guide to local exhaust ventilation, 2nd edn. http /Avww.hse.gov.uk/lev/index.htm... 

Despite the general outdoor nature of the work, construction workers are not immune from the hazards of airborne contaminants. Although natural wind movement will dilute dust and fumes throughout the site, operatives engaged on particular processes may have a dangerous concentration in their immediate breathing zones unless suitable extraction is provided. This is particularly relevant for work in shafts, tunnels and other confined spaces where forced draught ventilation may have to be provided. 

Local Exhaust Local exhaust ventilation is designed to capture airborne contaminants as near to the point of generation as possible. To protect you, the direction of contaminant flow must always be toward the local exhaust system inlet and away from you. 

It is also important to run checks on ventilation equipment to ensure it continues to operate at plarmed effectiveness levels. In some jurisdictions, mining law requires trained officers to regularly conduct air sampling for airborne contaminants. 

The ventilation airflow should proceed from areas of low contamination to areas of higher contamination in order to minimize the risk associated with the spread of airborne contamination. 

---