Health & Safety

Sandburg Garage Indoor Air Quality Survey


Evaluation of carbon monoxide (CO) and general hydrocarbon levels in the Sandburg Parking Garage during move-in day, September 2, 2000.

Placement of fan (left) near north tower staging area.


  • GasTec Passive Dosimeters (length of stain tubes)
  • MSA Passport 5-Star Multi-gas Monitor
  • Br�el & Kj�r Type 1302 Photoacoustic Gas Analyzer

Occupational Exposure Limits and Hygienic Values (2000): Carbon Monoxide:


OSHA PEL-TWA (8-hour): 35 ppm (1990 limit, vacated)

OSHA PEL-TWA (8-hour): 50 ppm (2000)


NIOSH REL (8-hour): 35 ppm

NIOSH "Ceiling" (15 minute exposure): 200 ppm

IDLH: 1,200 ppm


ACGIH TLV: 25 ppm

Odor Threshold: NA


  • Graph of exhaust levels near north-tower staging area
  • The time-weighted average CO level near the north tower staging area (CB1R) was 6 ppm; the average general hydrocarbon level was 3 ppm.
  • Dosimeter Tube Results:
    • 5 ppm near fan in southeast corner (CB1T)

    • 6 ppm near southwest corner (CB1S)
    • 4 ppm near ramp to lower level
    • 9 ppm near north tower parking meter (CB1R)
  • Peak reading with MSA Passport was 159 ppm, near north staging area during heavy traffic.


  • Time weighted average (TWA) values for CO were below the ACGIH hygienic level of 25 ppm.
  • CO levels around the perimeter of the garage were in the range of 0 to 10 ppm; CO and exhaust levels in the interior spaces were higher.
  • Exhaust levels were largely dependent on the volume of traffic at any given time. Exhaust and CO levels tend to be higher when cars leave the garage (i.e., from a cold start), opposed to when vehicles enter the facility and are working at normal operating temperature.
  • Exhaust values dropped significantly when a fan was relocated near the north staging area (see graph). This helped to dilute the exhaust, as well as providing some cooling-effect to those waiting in line. For future move-in days, we recommend placement of the fans in the interior spaces opposed to along the perimeter areas. Optimization of dilution of the exhaust may largely be due to trial and error.
  • Removal of the temporary east wall at the completion of the east tower construction should significantly increase flow-through ventilation and reduce exhaust levels below those recorded on 9/2/2000.

Updated November 16, 2007