With the development of accurate real-time monitors to measure aerosol and gas concentrations, the potential exists for the development of a feedback control system to automatically manipulate building ventilation rates in relation to contaminant levels. The proposed studies are concerned with the development of such a system with the use of an animal inhalation chamber. This device will allow for a controlled setting in which contaminant concentration and flow rate can be maintained at predetermined levels.
The specific aims of this study will be to investigate (l) the response of chamber concentration levels of cristobalite to various changes in dust generator speed and air flow rate and, (2) the use of statistical process control (SPC) techniques to implement feedback control of the concentration. Preliminary studies have been conducted to develop devices to automated the production of cristobalite with a computer controlled dust feed and chamber air valve actuator. This system has proven to be capable of producing and maintaining a chamber concentration level equivalent to a desired value chosen by the operator. The proposed studies will expand this system to incorporate feedback control based on information sent to the computer from a real-time aerosol monitor. We hypothesize the main difficulties to be overcome in the development of this system include: inconsistent response of the concentration level to a change in generator speed or flow rate and, a need to accurately predict the mean level of the chamber concentration when the reading exhibit a high degree of instantaneous variation. We will attempt to use an SPC technique known as an exponentially weighted moving average (EWMA) to both indicate the mean level and provide statistically derived control limits about the EWMA derived value to buffer the control system from spikes in the monitor readings which may cause an over-reaction of the control system. Results from this study will have immediate implications to the field of inhalation toxicology where strict control of chamber conCentration levels is important to results of dose- response relationships. We believe this information may also be of use to industrial hygienists involved with ventilation systems which use dilution air to control contaminant levels-in factories, mines and office buildings.
