Odors

General

Based on the assumption that the inability to find a difference between air pollutant levels in buildings with registered complaints and those without any complaints is due to inadequacies of prevailing measurement techniques, some investigators changed the focus from chemical analysis to sensory analysis. Some air pollution sources can be quantified by comparing them with a well-known source-a sedentary person in thermal comfort - by using a new measurement unit, the olf. An olf is defined as the emission rate of air pollutants from a standard person. Further discussion can be found in the ASHRAE Fundamentals Handbook chapter on Odors.

Outdoor sources of odors include automotive and diesel exhausts, hazardous waste sites, sewage treatment plants, compost piles, refuse facilities, abattoirs, printing plants, refineries, chemical plants, and many other stationary and mobile sources. Odors emitted by sources in the ambient environment eventually enter the indoor environment and can contribute to occupant discomfort.

Indoor sources also emit odors. Such sources include tobacco products, bathrooms and toilets, building materials (adhesives, paints, caulks, processed wood, carpets, plastic sheeting, and insulation board), consumer products such as food, toiletries, cleaning materials, polishes, hobby materials, fabrics and foam cushions.

In offices, offset printing processes, copiers, and computer printers may produce odors. If electrostatic processes are involved, ozone may be emitted. Mildew and other processes of decay often produce odors in occupied spaces and ventilation systems (e.g., from wetted air-conditioning coils and spray dehumidifiers).

Because the physicochemical correlates of olfaction are poorly understood, no simple analytical means to predict the perceived quality and intensity of an odorant exists. Moreover, since acceptability of an odorant depends strongly on context, it is unlikely that analytical instruments will supplant human evaluation.

Dilution of Odors by Ventilation

Comparisons of occupancy odor with smoke odor have been made by relating perceived odor intensity and odor acceptability during smoking and nonsmoking under controlled chamber conditions. When smoking took place, they found that the odor intensity was nearly five times as high as the odor intensity perceived under severe occupancy conditions (hot, humid, and low ventilation) but with no smoking. Determinations of the ventilation rates required to control occupancy odor and tobacco smoke odor to acceptable levels have been incorporated in the recently revised ASHRAE Standard 62 on Ventilation for Acceptable Indoor Air Quality.

Humidity and Temperature

Odor perception of cigarette smoke (which is a suspension of tobacco tar droplets plus vapor) and pure vapors is affected by temperature and humidity. An increase in humidity, at constant dry-bulb temperature, lowers the intensity level of cigarette smoke odor, as well as that of pure vapors. This effect is more pronounced for some odorants than for others. An increase in temperature at constant specific humidity lowers the odor level of cigarette smoke slightly. Adaptation to odors takes place more rapidly during the initial stages of exposure. Although the perceptible odor level of cigarette smoke decreases with exposure time, irritation to the eyes and nose generally increases. The irritation is greatest at low relative humidities.

To keep odor perception and irritation at a minimum, the air-conditioned space should be operated at about 45 to 60% relative humidity. Because temperature has only a slight effect on odor level at constant specific humidity, it generally can be ignored; temperature should be maintained at conditions desired.

Links to Related Topics

Commissioning
Building Reuse
Humidity Control
Smoke
Sick Building Syndrome