Issue link: https://hi.iaq.net/i/630729
112 Appendix A amount in a single puff. (Note: Avoid direct inhalation of chemical smoke, because it can be irritating. Do not release smoke directly on smoke detectors.) Using the Results Smoke released mid-room: Observation of a few puffs of smoke released in mid- room or mid-cubicle can help to visualize air circulation within the space. Dispersal of smoke in several seconds suggests good air circulation, while smoke that stays essentially still for several seconds suggests poor circulation. Poor air circulation may contribute to sick building syndrome complaints or may contribute to comfort complaints even if there is sufficient overall air exchange. Smoke released near diffusers, grilles: Puffs of smoke released by HVAC vents give a general idea of airflow. (Is it in or out? Vigorous? Sluggish? No flow?) This is helpful in evaluating the supply and return system and determining whether ventilation air actually reaches the breath- ing zone. (For a variable air volume system, be sure to take into account how the system is designed to modulate. It could be on during the test, but off for much of the rest of the day.) "Short- circuiting" occurs when air moves relatively directly from supply diffusers to return grilles, instead of mixing with room air in the breathing zone. When a substan- tial amount of air short-circuits, occupants may not receive adequate supplies of outdoor air and source emissions may not be diluted sufficiently. Carbon Dioxide (CO 2 ) as an Indicator of Ventilation CO 2 is a normal constituent of the atmo- sphere. Exhaled breath from building occupants is an important indoor CO 2 source. Indoor CO 2 concentrations can, under some test conditions, provide a good indication of the adequacy of ventilation. Comparison of peak CO 2 readings between rooms, between air handler zones, and at varying heights above the floor, may help to identify and diagnose various building ventilation deficiencies. Methodology CO 2 can be measured with either a direct- reading meter or a detector tube kit. The relative occupancy, air damper settings, and weather should be noted for each period of CO 2 testing. CO 2 measurements for ventilation should be collected away from any source that could directly influence the reading (e.g., hold the sampling device away from exhaled breath). Individual measurements should be short-term. As with many other measurements of indoor air conditions, it is advisable to take one or more readings in "control" locations to serve as baselines for comparison. Readings from outdoors and from areas in which there are no apparent IAQ problems are frequently used as controls. Outdoor samples should be taken near the outdoor air intake. Measurements taken to evaluate the adequacy of ventilation should be made when concentrations are expected to peak. It may be helpful to compare measure- ments taken at different times of day. If the occupant population is fairly stable during normal business hours, CO 2 levels will typically rise during the morning, fall during the lunch period, then rise again, reaching a peak in mid-afternoon. In this case, sampling in the mid- to late-after- noon is recommended. Other sampling times may be necessary for different occupancy schedules. Using the Results Peak CO 2 concentrations above 1000 ppm in the breathing zone indicate ventilation problems. Carbon dioxide concentrations below 1000 ppm generally indicate that ventilation is adequate to deal with the routine products of human occupancy.