Page 30 - Occupational Health & Safety, February 2018

INDUSTRIAL HYGIENE
Each system includes a “sensor suite” built to accept a variety of sensors for multipoint sampling of the indoor environmental pa- rameters. The sensor suite analyzes each air packet and sends smart signals to optimize ventilation. A total of 34 sensor suites were installed, with two more planned for a vi- varium on the Evanston campus.
System Offers Transparent Communication
Transparent communication with the labo- ratory users is important because most of the sensors and control elements are hid-
den from view. Additional touch screens were installed in laboratories to provide feedback on current ventilation settings. Researcher adherence to operational limits is considered to be more important in labo- ratories where the air change rates can be below 4 ACH.
Capabilities and Limitations of Optimization System Controls
The optimization system’s sensor suite ca- pabilities to measure carbon dioxide (CO2) and dewpoint are most interesting in non- laboratory applications. CO2 and dew point
sensors are in use in some non-laboratory and vivarium settings.
For laboratory applications, the opti- cal particle counter counts small particles (PM2.5) in one range: 0.3-2.5 microns (μm). For vivarium applications, particles can be counted in two ranges: 0.3-0.5μm and 0.5-2.5μm. This feature can be useful to verify HEPA filter integrity on the supply side and efficiencies in clean space opera- tions. The installed system commands the lab control system to dynamically increase the laboratory air changes above a particle count of 500,000 per cubic foot of air. This is accomplished by opening control valves in the ventilation ductwork of the affected space and also may affect the variable-fre- quency drive (VFD) controls of the ventila- tion fans. The system calls for the highest air change rate at and above 5,000,000 par- ticles per cubic foot.
For laboratories, the most useful capa- bility is the sensing of TVOC, either using a metal oxide semiconductor (MOS) or a photoionization detector (PID) calibrated to isobutylene. The PID can be calibrated to both ammonia and isobutylene. Once a sample air packet reaches the sensor suite, the response time is 30 seconds. The ac- curacy of the PID is ± 0.2 parts per mil- lion (ppm) or 2.5% of reading (whichever is greater). The resolution of the PID is 0.025ppm. The drift stability of the PID is ± 2ppm/6 months @ 5ppm isobutylene. The maximum TVOC range is 100 ppm for the MOS and 20 ppm for the PID. According to the optimization system vendor, the MOS sensor provides complementary detection capabilities, as it will detect parameters (including but not limited to methanol, methane, nitromethane, and methylene chloride) that are either not sensed or only poorly sensed by the PID.
The ventilation optimization system commands the lab control system to dy- namically increase the laboratory air changes above 0.1 ppm on the PID or 0.3 ppm on the MOS. It calls for the highest air change rate at and above 1 ppm on the PID and 3 ppm on the MOS.
Exposure Control and
Life Safety Considerations
The optimization system cannot take on life safety tasks or be used in lieu of dedicated toxic, flammable, or oxygen depletion gas alarm systems. The system should only be
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