Occupational history
In 2000 a 45 year old Caucasian male worker (never smoker) started to work in a RCF processing plant. For the first three years he was employed at a suction station for processing vacuum mouldings by transferring RCF manually from packages into the suction station. He also operated a dry kiln for these vacuum mouldings. After drying the vacuum moulds they had to be cut or sawed to length manually, polished, and holes had to be drilled to attach heating units. The heating units were glued and clenched to the moulds. Finally two half-round moulds were assembled to form one round heating furnace. While working at the suction station and especially at the dry kiln, dust concentrations of RCF were measured. Since 2004 he was assigned to the cartridge production line also working at the works bench with a lower exposure to RCF.
Personalised measurements were taken at different production sectors within the plant in 2012, 2015, 2017 and 2018 as shown in Table 1.
Table 1:
Personalised measurements of RCFs at different production sectors in Fibres per cm³
production sector
|
2012
|
2015
|
2017
|
2018
|
suction station 1
|
|
0,037
|
0,120
|
|
suction station 2
|
0,293
|
0,118
|
0,30
|
|
suction station 3
|
|
|
0,270
|
0,256
|
kiln
|
0,781
|
0,492
|
0,650
|
0,766
|
saw position 1
|
|
0,35
|
0,64
|
0,30
|
saw position 3
|
|
1,10
|
1,21
|
0,99
|
work bench
|
|
|
0,34
|
0,31
|
booth M9
|
|
0,11
|
|
0,15
|
cartridge production
|
|
|
|
0,32
|
final assembly
|
|
|
|
0,14
|
Clinical examination
The worker performs endurance sport as running and soccer playing on a regular base. No pulmonary disease has been described before. No complaints were reported while being exposed to fumes, gases, dust or being in wet and cold weather. Breath sounds were reduced in the lower left side and the percussion note was dull. Lung expansion was decreased on the left side. Crackles could not be detected.
Lung function analysis
In 2018 restrictive lung function was revealed during an occupational medical examination. For grading the pulmonary function, VC, FEV1, TLC, RV, DLCO, DLCO/VA, ITGV, and MEF50 were expressed and analysed as a percent of the predicted value in the reference population (pred.) as recommended by the guidelines GLI 2012 (5-11). In our outpatient clinic lung function analysis confirmed a reduced vital capacity (VC) of 3.35 L with a lower limit of normal (LLN) of 4.01 L according to GLI 2012. Forced expiratory volume in 1 second FEV1 was reduced with 2.8 L (LLN 3.18 L) whilst FEV1/FVC ratio 82% (LLN 69%) was normal. The defusing capacity (DLCO) of 7.93 mmol/min/KPa (pred. 8.34 mmol/min/KPa) was reduced as well as residual volume divided by total capacity (RV/TC) 28% (pred.: 41%) and total gas volume (TGV) 2.6 L (pred.: 4.44 L) .
Radiological findings
In chest X-rays (p.a. and lateral) showed localised pleural thickening with adhered costodiaphragmatic sinus on the left side and consecutively reduced volume of the left hemi thorax (Figure 1).
Computer tomography scans presented bilateral pleural thickening especially paravertebral, with embedded pleural calcification. Besides this a beginning rounded atelectasis with a “comet tail” sign is visible adherent to the pleura in the left. A volume reduction of the left lower lobe (Figure 2) is seen.
Analysis of the insulating material
Techniques used for the material characterisation
RC Fibre samples (aluminium silicate fibres) called F3, F17 and F14 obtained from the processing plant as raw material RCF (indicated a) and RCF vacuum moulds (indicated b) were analysed. Scanning electron microscopy (SEM; Hitachi S-2300; Hitachi, Ltd., Tokyo, Japan) was used to identify fibre geometry in addition to the microstructure of the fibres. Energy dispersive X-ray spectroscopy (EDX) was used to determine the elementary composition. To increase the conductivity, all samples were sputtered with a fine layer of Au.
X-ray powder diffraction is a common technique to determine the crystal structure of materials. It was used to analyse the crystallinity of the RCF. X-ray powder diffraction in reflection mode was performed with an X’Pert Pro from PANalytical (CuKα radiation (λ = 1.5418 Å), 40 kV, 40 mA). The measurements occurred between 10° and 80° with a step size of 0.033°. With this technique, monochromatic X-ray radiation, generated by a cathode ray tube, creates constructive interference with the sample when the conditions fulfil Bragg’s law:
(1)
Here n is an integer, λ is the wavelength of the monochromatic X-ray radiation (most common: CuKα radiation λ = 1.5418 Å), d is the distance between two lattice planes and θ (Theta) is the diffraction angle.
The intensity of the diffracted beam is detected in dependence of the angle 2θ, measured in degree (deg), between the incident beam and the detector. The resulting diffraction “peaks” (reflections) can be converted into d-spacings, which allows the identification of the material since these d-spacings are unique for each compound. While crystalline substances produce a pattern of sharp reflections with different intensities, amorphous compounds only produces a broad background signal. Further information about this technique can be found, for example, in the review article of Bunaciu et al. (12).
The crystallinity of the RC fibres was additionally investigated with transmission electron microscopy (TEM) and electron diffraction. The TEM images were recorded with a Philips CM30/STEM (300 kV, LaB6 cathode) equipped with a GATAN digital camera.
In figure 6 the results of the X-ray powder diffraction of the samples F3 and F17 were presented. The raw material (indicated a) as well as the RCF vacuum moulds (indicated b) showed no reflections, only a broad background signal, which indicates the amorphous character of these samples. The electron diffraction confirms these results; no reflections were visible as well.
In contrast, the fibres of the samples F14 are crystalline. The X-ray powder diffraction (Fig. 7) of the sample F14a and F14b shows sharp reflections for specific angles, which indicates the crystallinity of this sample. The fibres were identified with a crystallographic data base by the diffraction pattern as mullite (3Al2O3∙2SiO2).
The electron diffraction confirms these results. Figure 9 shows the electron diffraction pattern of the samples F14a and F14b. The different arrangement of the reflections originates from different crystallographic orientations of the fibres. The distance between the centre and the reflections can be converted into d-spacings, which can be assigned to the Miller indices shown in figure 8.
The lattice planes are usually depicted through the Miller indices h, k, l. These three digit numbers describe the orientation of a single lattice plane or a set of parallel planes and result from the points, where a plane cuts the crystallographic axes (a, b, c). The Miller indices are depicted in curvilinear bracket as (hkl). Further information about crystallography can be found, in the review article of Ameh (13).