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
Standard | Limits |
---|---|
OSHA | 8-hour TWA: 50 ppm |
NIOSH | 8-hour PEL- TWA: 35 ppm |
ACGIH | 8-hour TLV – TWA: 25 ppm |
International Mechanical Code section 404.1 | Mechanical 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
Concentration | Alarm 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.