Objective To evaluate the uncertainty in determining free silica in dust of workplace by pyrophosphoric acid method.

Methods According to the Evaluation and Expression of Uncertainty in Measurement(JJF 1059.1-2012) and the Method for Determination of Dust in the Air of Workplace Part 4:Content of Free Silica in Dust(GBZ/T 192.4-2007), the uncertainty of pyrophosphoric acid method was sourced, evaluated and combined.

Results The repeatability and temperature were the main sources of uncertainty components in the determination process. The relative standard uncertainty of repeatability without treatment by hydrofluoric acid was 8.89×10^-2, and the relative standard uncertainty of repeatability after treatment by hydrofluoric acid was 5.90×10^-2; the relative standard uncertainty of temperature by thermometer calibration was 0.26×10^-2, and the relative standard uncertainty of temperature by muffle furnace calibration was 0.12×10^-2. The combined standard uncertainty of free silica in dust at workplace without treatment by hydrofluoric acid was 1.35%, and the expanded standard uncertainty was 2.70%;the combined standard uncertainty of free silica in dust at workplace after treatment by hydrofluoric acid was 0.57%, and the expanded standard uncertainty was 1.14%. The results of the standard uncertainty of free silica in dust at workplace were (15.18 ±2.70)% without treatment by hydrofluoric acid and (9.66 ±1.14)% after treatment by hydrofluoric acid.

Conclusion Except for maintaining the precision, operability and repeatability of all used weighing instrument, to strengthen the operation training and familiarity with the whole process of operation will reduce the uncertainty.