Asbestos air and dust test results, BMCC, Feb 2002

NYC 9/11 Public Portal Document

B.M.C.C. Page 5 Dust & VOC Levels November 14, 2001 APPENDIX A: AIR MONITORING METHODS AND INSTRUMENTATION

1. Dust Trak Aerosol Monitor

The TSI Model 8520 Dust Trak Aerosol Monitor is a laser photometer, which uses light scattering technology to determine mass concentration. The sensing mechanism consists of a laser diode directed at the aerosol stream. The laser diode has a wavelength of 780 nanometers (nm) which limits the smallest detectable particle to about 0.1 pm. Scattered light is collected with optics and a photodetector at 900 to the light beam. The intensity of the scattered light is a function of the particle mass concentration, and the results are expressed in units of mass per volume (mg/m3). The instrument has a sample flowrate of 1.7 Umin. Particle measurements can be taken at 1.0, 2.5, 4.0, and 10.0 pm diameters. Inlet conditioners (impactors) are used to limit the upper size particle ranges to 1.0 and 2.5 pm. Additionally, a 10-millimeter cyclone is used for respirable sampling with a particle size cut-off at 4 pm (internationally accepted as the 50% cut-off size for respirable aerosol mass). The mass concentration range for the instrument is 0.001 to 100 mg/m3; the particle size range is 0.1 to 10 pm.

2. Photo Ionization Detector

The Mini-RAE 2000 Photo Ionization Detector (PID) is used for the measurement of most VOCs, down to a level of 0.1 ppm, with an accuracy of +/- 2%. The sensor consists of a sealed UV light source that emits photons which are energetic enough to ionize many trace species (particularly organics) but do not ionize the major components of air such as oxygen, nitrogen, carbon dioxide, carbon monoxide, or water.

The field created on an electrode will drive any ions formed by adsorption of the UV light to the collector electrode where the current (proportional to concentration) is measured. Response time for this direct reading instrument is under 5 seconds. The instrument was calibrated on site using a zero gas calibration setup (using a charcoal filter to exclude any organic gas) and a known concentration of 100 ppm isobutylene.

The findings presented in this report were valid during the times the survey was conducted and within the scope of TBE's protocol as discussed above.

NYC-WTC 000106398