Contamination, sources

During the site visit, auditors should identify any potential groundwater contamination sources or unusual odors observed at the facility. If any, explain. 

Indoor air contaminants can originate within the building or be drawn in from outdoors. If contaminant sources are not controlled, problems can arise, even if the HVAC system is properly designed and well-maintained. Sources can be from outside the building from operating equipment, from human activities, and other or miscellaneous sources. Sources outside a building include contaminated outdoor air, emissions from nearby sources, soil gas, or moisture or standing water. 

Check the outdoor air intakes to see whether they are located near contaminant sources (e.g., plumbing vents, exhaust outlets, dumpsters, loading docks, or other locations where vehicles idle). See if the space containing the HVAC system is clean and dry. Examples of problems include cleaning or other maintenance supplies... 

An initial walkthrough of the problem area provides information about all four of the basic factors influencing indoor air quality (occupants, HVAC system, pollutant pathways, and contaminant sources). The initial walkthrough may provide enough... 

If the hypothesis or model does not seem to be a good predictor of what is happening in the building, you probably need to collect more information about the occupants, HVAC system, pollutant pathways, or contaminant sources. Under some circumstances, detailed or sophisticated measurements of pollutant concentrations or ventilation quantities may be required. Outside assistance may be needed if repeated efforts fail to produce a successful hypothesis or if the information required calls for instruments and procedures that are not available in-house. Analysis of the information collected during the LAQ investigation could produce any of the following results ... 

Pollutant pathway information helps the investigator to understand airflow patterns in and around the complaint area. The pollutant pathway data may indicate a need to enlarge the complaint area, or may direct attention toward contaminant sources that deserve close study. 

Ventilation modification is often used to correct or prevent indoor air quality problems. This approach can be effective either where buildings are underventilated or where a specific contaminant source cannot be identified. Ventilation can be used to control indoor air contaminants by ... 

Ventilation equipment can be used to isolate or remove contaminants by controlling pressure relationships. If the contaminant source has been identified, this strategy can be more effective than dilution. Techniques for controlling air pressure relationships range from adjustment of dampers to installation of local exhaust. 

Fleikkinen, M, Study of Contaminant Sources in the Manufacturing hidustry, Proceedings of the 4th International Symposium on Ventilation for Contaminant Control, Stockholm, Sept S-9, 1994. 

Knowledge of the process or operation and contaminant sources is essential before ventilation systems can be selected and designed. Contaminant sources affecting the working environment may be external, associated with the elements of HVAC systems, or internal. 

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. 

Theories of hood performance with nonbuoyant pollution sources are based on the equation of turbulent diffusion. The following equation allows the engineer to determine the contaminant concentration decay in the uniform airflow upstream from the contaminant source ... 

The geometry of the contaminant source can be compact or linear. The source geometry affects the hood geometry round, rectangular, or slot. 

For nonenclosing hoods, the airflow rate that allows contaminant capture is called a target airfloitO The target airflow rate is proportional to some characteristic flow rate Qg that depends on the type of contaminant source ... 

For a nonenclosing hood with a nonbuoyant contaminant source, the characteristic airflow can be calculated using the following equation ... 

The following equations separately outline calculating contaminant concentration inside a room with central and local recirculation. The assumptions for the room are that it has one main ventilation system with supply and exhaust air and that the contaminant concentration is the same in the whole volume (except very close to the contaminant source or in the ducts, etc.). The contaminant source is steady and continuous. The model for local ventilation assumes also one main ventilation system to which is added one local exhaust hood connected to a local ventilation system (see Chapter 10) from which all the air is recirculated. In the central system the number of inlets and outlets could vary. The flow rates are continuous and steady. 

Typically, when central recirculation is used the contaminant in the supply air is the main source. This is not the case for industrial use, where the main source is in the ventilated room. This usually results in the concentration being somewhat higher when using recirculation than when not using it. Figure 8.1 outlines the ventilation system, the contaminant source, and the cleaning system. 

FIGURE 8.1 Model of a central recirculating system used for calculating the connection between contaminant concentrations, airflow rates, contaminant source strength, q, and air cleaner efficiency, rj. Cj p is the concentration in the supply (outside) air, c is the concentration in the room, c is the concentration in the returned air, (JaMot the total flow rate through the room, ic is the ratio between recirculated airflow rate and total air flow rate, T is the time constant for the room, and V is the room volume. 

One of the most common systems for cleaning air in homes, offices, schools, etc. is the room air cleaner. Figure 8.2 outlines a model of a local recirculating system. Usually these units are situated inside the room if they are small and movable (see Chapter 10). For the model it does not matter if the unit is placed inside or outside the room with the contaminant source, as long as the exhaust and return air openings are inside. 

The convection flows from the heat sources V and Z as well as contaminant flows from contaminant sources are flows loading the room. In the sources additional heat and pollutant flows may be generated, which are exhausted directly out by local ventilation and are not included in the balance calculation. 

The contaminant removal effectiveness can be used when emission data for contaminant sources are available. 

When detailed information on heat and contaminant sources is available, assessment of design is improved by evaluating the effectiveness of contaminant removal achieved by space ventilation. The set of contaminant removal effectiveness indices in Table 8.5 is given in accordance with contemporary use of indices. 

Application of the age of air concept can be justified by the fact that the content of contaminants found in the exhaust air normally rises from the value found in supply air entering the room. On its voyage through the room, the air is likely to pick up more contaminants the longer it stays in the room. This is a very simple assumption. It can be argued, however, that using the age of air concept is the best way to evaluate ventilation design for scenarios where little or no information is available on use of the room and locations and emission rates for heat and contaminant sources. 

In the stratification strategy the supply air is used to substitute the outgoing air from the ventilated (in most cases occupied) zone, thus preventing circulation patterns between the zones. The supply air has to be distributed in such a way that the buoyancy flows are not disturbed. Exhaust air openings are to be located downstream in order to avoid reverse currents within the room. The location of the contaminant sources and the heat sources causing density differences must be the same in order to carry out the contaminants with equal or higher density than air. 

K. Hagstrom, A. Zhivov, K. Siren, and L. L. Christianson, The influence of heat and contaminant source non-uniformity on the performance of three different room air distribution methods. ASHRAE Transactions, 1999, 2, 105. 

---