Determination of amorphous silica in the alveolar dust fraction (A-dust) according to IFA 7710 & IFA 6068

Sampling

For sampling A-dust the following sampling systems are available at the GSA: 

• SG10-2 with FSP-10 (personal sampling)   
• PM4-2 with fine dust head (stationary sampling)
• VC25-2 with fine dust head (stationary sampling) 

Prior to the determination of amorphous silica (silica glass, silica material, silica smoke, diatomaceous earth) in the alveolar dust fraction, the mass of A-dust on the filter medium to be analysed must be determined.

We recommend to choose a measuring duration so that a volume of 2 m³ is reached in order to be able to detect 1/10 of the limit value (0.3 mg/m³).

Analysis

• FTIR spectrometer Spectrum TWO and Spectrum 100 by Perkin Elmer

Preparation of sampling

The collected cellulose nitrate filter is incinerated with the aid of a cold ashing device under oxygen supply. In the cold ashing device (60 °C), the filter substrate as well as interfering organic components of the dust sample are oxidised away. The resulting residue is then homogenised with potassium bromide and pressed into a compact. 
 

Evaluation

An absorption spectrum in the range of 4000 cm-1 to 400 cm-1 is recorded from this compact with the aid of the FTIR spectrometer, which is then used for evaluation. Furthermore, a pure specific reference sample of the amorphous silica to be analysed is required in order to be able to record a calibration or comparison spectrum.

The detection limit here is 20 µg absolute. We recommend to analyse a blank value.

Limit value

The occupational exposure limit for fired amorphous silica is 0.3 mg/m³ in the alveolar dust fraction (A-dust) according to TRGS 900. The occupational exposure limit for unfired amorphous silica is 4.0 mg/m³ in the inhalable dust fraction (E-dust) according to TRGS 900.