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Monitoring Carbon Monoxide
in Parking Garages and Tunnels

A description of a system installed in a parking garage and a tunnel in Switzerland follows:


During installation, sensors are strategically located, taking into consideration airflow around each sensor. In the tunnels, sensors are located approximately 50 to 150 feet apart. They are mounted near shoulder height, making them easily accessible for maintenance and calibration. In parking garages, sensors are located near the ceiling, between adjacent parking aisles or at intersections of roadways within the garages.

Sensors are designed for monitoring concentrations from 0-300 or 0-500 PPM. Each sensor/controller can activate relays (one WARN, one ALARM) at different concentration levels. A typical WARN (LOW LEVEL) activate point is 50 PPM, and ALARM (HIGH LEVEL) is 150 PPM.


At 50 PPM, a 3 minute timer is activated. If gas is still present (above 50 PPM) after 3 minutes, the WARN relay is activated, turning on a low speed fan. When the concentration drops below 50 PPM, the WARN relay is deactivated, and the fan shuts off. If the CO concentration increases over 150 PPM, a high speed ventilation fan is activated and a 15-minute timer is started. Should the CO level remain over 150 PPM for 15 minutes, the timer activates an audible or visual alarm advising management of the situation. Management determines the appropriate course of action. The timers are used to prevent frequent activation and deactivation of fans due to heavy momentary traffic near a sensor location, and helps conserve energy.

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View/download PDF versions of:

Gas Sensor Selection Guide (File size: 196K)

Hazardous Gas Data - comprehensive reference on physical and chemical properties for industrial hygiene and occupational health & safety applications (File size: 396K)

PID Correction Factors - a comprehensive reference on PID correction factors for 222 gases (File size: 100K)

Installation & Instructions Manuals for:
MP Controller (File size: 1.1MB)
b) 4-20 IQ (File size: 536K)
SM95 (File size: 567K)

How to Calibrate Sensors
(File size: 427K)

Introduction - from "Hazardous Gas Monitors" book (24 pages)- includes descriptions, "Terms, Definitions & Abbreviations," fully illustrated with charts and graphs, and types of protection (File size: 544K)

About Alarms (File size:148K)

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