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Evaluation of Optical Instruments for Real-Time Continuous Monitoring of Smoke Particulates
Tests were conducted in three phases: 1998 laboratory tests, field tests conducted in the fall of 1998 and 1999, and laboratory tests conducted in the spring of 2000. While the primary focus of these tests was to determine the accuracy and to compare the results from several identical instruments, operational and reliability characteristics were also being evaluated.t
Objectives—The objectives of the 1998 laboratory tests were to determine whether the optical and gravimetric instruments showed significant differences when measuring smoke particles produced from burning biomass under controlled conditions. If possible, we hoped to determine a correction curve for the optical instruments. A report on these tests, Laboratory Evaluation of Two Optical Instruments for Real-Time Particulate Monitoring of Smoke (9925-2806-MTDC, figure 7), was published in 1999.
Figure 7—A report (9925-2806-MTDC)
was published in 1999 detailing the
laboratory evaluation of two real-time
particulate monitors.
Location—The laboratory tests were conducted at the Fire Sciences Laboratory's large (131,000 ft³) combustion chamber. The instruments were placed side by side and operated on a platform 55 ft above the chamber floor (figure 8).
Figure 8—Instrument layout on the smoke-
sampling platform in the combustion chamber.
Instruments—Two optical instruments were evaluated in the 1998 laboratory tests, the MIE DataRam and the Radiance Research nephelometer. The MIE DataRam was configured with a PM2.5 cutoff device and inlet heater. The Radiance Research nephelometer measured total suspended particulate. Two different gravimetric devices were used, an FRM PM2.5 sampler manufactured by Rupprecht and Patachnick and a PM2.5 sampler developed by the Fire Sciences Laboratory for airborne smoke studies. The FRM was available only for a few tests. The Fire Sciences Laboratory's gravimetric sampler was used for all tests.
Test Descriptions—The experiments were conducted at ambient conditions inside the closed chamber at temperatures of 70 to 90 °F and 30- to 50-percent relative humidity. Small beds of flaming and smoldering ponderosa-pine needles on the chamber floor generated the smoke for most of the tests (figure 9). Several tests were conducted using smoke generated from burning duff. A total of 66 tests were conducted. The duration for each test varied depending on the estimated particulate concentration. Higher concentration tests were shortened to prevent clogging the filters. Lower concentration tests took longer to accumulate enough mass on the filters for accurate weighing. The average test took about an hour.
Figure 9—An example of the fire beds
of pine needles used to produce smoke
in the laboratory combustion chamber.
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