NYC-WTC_000230933

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4.3 Air Sampling Procedures

ALC's licensed technicians collected air samples using TEM Methodology. The technician collected five (5) air samples on each floor. The samples were taken in three (3) apartments and at two separate areas in the hallways on each floor. The technician identified the locations that appeared to contain the most visible dust and debris to perform, sampling.

The air samples were collected using high volume air sampling pumps. Once the pumps were in place the air sampling technician recorded the location, time, date, sample numbers, pump number, flow rate, start and stop times and his initials.

The air cassette was independent of the pump motor. Thi.s is to prevent the vibrations of the motor from affecting die fibers in the cassette. A separate stand or tripod was used to hold the cassette in place. The cassette was angled 45 degrees downward from the horizontal stand. This is to insure that no asbestos will drop into the cassette while sampling.

Using a rotameter, we calibrated each pump to the required flow rate, noting this rate on the sample record. After calibrating the pumps, the end cap from the cassette was removed; the pump was turned on and run for the required amount of time.

The sampling pumps were checked periodically to ensure they were still operating, the cassettes were still in place, and no one has disturbed the equipment. If at any time the area being sampled was suspected of having high fiber counts, the filter inside the cassettes were examined for “overloading”, or an excessive amount of fibers and/or debris on the filter.

When the pre-determined volume of air has been collected, the technician then calibrated the sampling pump again to determine the current flow rate. This rate will often be different from the flow rate measured at the beginning of the sampling period. That difference is usually’due to the clogging of the filter, thereby adding increased resistance to the flow of air.

Once the pre-determined volume of air has been reached, the time was recorded as well as on the cassette. Before the pump was turned off, the cassette was angled upward and the cap replaced and the end plug. The cassettes were placed in sealed containers, labeled with an identifying code and a sample log was kept. The samples were then submitted to the laboratory to be analyzed for asbestos content. A chain of custody record was prepared and accompanied the samples to the laboratory.

4.3. Asbestos Analysis and Methodology

Each air sample is cross-referenced by field designation and lab internal code to ensure proper, consistent handling through a chain of custody. Sample preparation takes place within a HEPA Filter clean bench to avoid any possible contamination. Air sampling was conducted at a level approximating the breathing zone of persons anticipated to be present in the area during normal operations. Samples collected represent the typical airborne fiber concentration of the area.

5. Findings and Conclusions

Twelve (12) initial background air samples were collected and analyzed via phase contrast microscopy (PCM) at building 300. Seven (7) samples were analyzed via Transmission Electron Microscopy (TEM). Afier analysis via TEM. all were below the ccrmissiblc limits.

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