Exhaust emissions of CO and NO2 are generated in parking garages as part of normal operations. While normal air exchange ventilation may minimize concentration build up, excessive concentrations can pose a health hazard. Continuous fan operation can be used to reduce emissions concentration but this increases maintenance costs, decreases system life, and increases energy costs. Using a gas detection system provides control for ventilation fans as well as alarming if gas concentrations reach unsafe levels.

Carbon Monoxide Safety Limits and Standards

StandardLimits
OSHA8-hour TWA: 50 ppm
NIOSH8-hour PEL- TWA: 35 ppm
ACGIH8-hour TLV – TWA: 25 ppm
International Mechanical Code section 404.1Mechanical ventilation systems for enclosed public garages shall be automatically operated by means of carbon monoxide detectors applied in conjunction with nitrogen dioxide detectors.

Typical Action and Alarm Levels for Monitoring System

ConcentrationAlarm Action
CO (35 ppm), NO2 (2.5 ppm)Engage ventilation
CO (75 ppm), NO2 (2.8 ppm)Additional ventilation
CO (100 ppm), NO2 (3 ppm)Horn and strobe alarm

The safety standards above are based on 8-hour time-weight averages. Using the recommended alarm actions ventilation occurs at the first measurement of 35ppm concentration of CO and provides a significant safety factor against the 8-hour average.

Sensor Placement

Sensors should be placed in areas where there is little or no air movement and in locations of good air circulation but not in the path of rapidly moving air which is likely to have diluted concentrations of CO and NO2. Sensor location at entrances to the parking facility, elevators, makeup air fans and any other sources of active air currents should avoided as this will result in reduced concentration readings in these areas but not areas with less air flow.  Sensors should be located in the “breathing zone” which is about 4-6’ from the floor. Sensors do not provide a “radius of coverage”, but quantity estimates can be determined by planning for one sensor for every 5,000 ft2 (465 m2).

Bacharach Solutions for Parking Garage Emissions

The Bacharach MGS-550 dual-channel gas detector has sensors for CO (0-500ppm) and NO2 (0-20ppm). Outputs include 3 relays, 2 analog outputs, and Modbus communications enabling flexible system design for alarming and ventilation fan control. The MGS-550 has an IP66 rated ABS enclosure that provides protection from dust and water intrusion.

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