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Table 3.2.4 Relationship Between Final Canister Vacuum, Volume Sampled, and Dilution Factor (6 L Canister) Final Vacuum (in. Hg) 0 2.5 5 7.5 10 12.5 15 17.5 20 Volume Sampled (L) 6 5.5 5 4.5 4 3.5 3 2.5 2 Dilution Factor* 1.34 1.46 1.61 1.79 2.01 2.30 2.68 3.22 4.02 Canister pressurized to 5 psig for analysis was high. Once the vacuum decreases below 5 in. Hg, the flow rate begins to drop significantly. This scenario indicates that the sample is skewed in favor of the first portion of the sampling interval. • If the final vacuum is near ambient (i.e., less than I in. Hg), there is inadequate differential pressure to drive the flow controller. The sampler cannot be certain the desired sampling interval was achieved before the canister arrived at ambient conditions. The sample could have been acquired over a 1-hour interval (which would be the case if the connection between the canister and flow controller leaked or if the flow controller malfunctioned) or a 24-hour interval. Al- though the actual sampling interval is uncertain, the canister still contains sample from the site. 3.2.5 Considerations for Integrated Sampling with Canisters Collecting an integrated air sample is more involved than collecting a grab sample. Sampling considerations include verifying that the sampling train is properly configured, monitoring the integrated sampling progress, and avoiding contamination. • Avoid Leaks in the Sampling Train: See Section 3.1 for instructions on how to securely assemble sampling hardware. A leak in any one of these connections means that some air will be pulled in through the leak and not through the flow controller. A final pressure near ambient is one indication that there may have been a leak. • Verify Initial Vacuum of Canister: See Section 3.1. for instructions on verifying initial canister vacuum. If you are using an Air Toxics Ltd. critical orifice flow controller, note that you can use the built-in gauge. It is important to note both the canister and flow controller serial numbers on the chain-of-custody. (CD-A I R TOXICS LTD. 13