TABLE 5. INTRALABORATORY RESULTS FOR EVALUATION OF XRD SILICA METHOD.
| Item | Filter Loading | ||
| 69.4 µg/filter | 98.4 µg/filter | 204 µg/filter | |
| Degrees of Freedom | 12 | 11 | 12 |
| RSD for sampling and analytical methods (%)*, † | 8.8 | 6.3 | 8.1 |
Source: NIOSH, BOM [1983].
* RSD = relative standard deviation. RSD for sampling and analytical methods represents the RSD in mass estimates, accounting for intersampler and analytical variability.
† Implications for XRD: Pooled filter levels and pump error (assumed to be <5%) indicate that the overall imprecision is as follows: Total RSD for sampling and analytical methods is 9.3%. Therefore, the upper 95% confidence limit on the accuracy (35 degrees of freedom) is 21%.
TABLE 6. INTRALABORATORY RESULTS FOR EVALUATION OF IR SILICA METHOD.
| Item | Filter Loading | ||
| 67.2 µg/filter | 99.7 µg/filter | 161 µg/filter | |
| Degrees of Freedom | 10 | 12 | 11 |
| RSD for sampling and analytical methods (%)*, † | 5.8 | 7.8 | 7.4 |
Source: NIOSH, BOM [1983].
* RSD = relative standard deviation. RSD for sampling and analytical methods represents the RSD in mass estimates, accounting for intersampler and analytical variability.
† Implications for IR: Pooled filter levels and pump error (assumed to be <5%) indicate that the overall imprecision is as follows: Total RSD for sampling and analytical methods is 7.1%. Therefore, the upper 95% confidence limit on the accuracy (33 degrees of freedom) is 17%.
The airborne concentrations of silica to which these filter loadings correspond depend on the flow rate of the pre-sampler used. Currently the Occupational Safety and Health Administration (OSHA) uses the 10-mm Dorr-Oliver nylon cyclone at a sampling rate of 1.7 L/min. The concentrations relevant to the collaborative test conditions are listed in Tables 7 and 8 and assume an 8-hour sampling period. As indicated, the traditional nylon cyclone passes the accuracy criterion over a range of concentrations bracketing 100 µg/m3 (the current OSHA PEL) (see nylon cyclone data in Tables 7 and 8). In addition, since the new BGI GK2.69 cyclone (discussed in Section 4 of this chapter) is expected to conform to the ISO/CEN/ACGIH respirable aerosol sampling convention, the NIOSH accuracy criterion was applied using the 4.2 L/min sampling rate of the GK2.69 cyclone. The GK2.69 cyclone evidently is accurate over a range of concentrations bracketing 50 µg /m3 (0.5 times the current OSHA PEL) (see GK2.69 cyclone data in Tables 7 and 8).
