INDUSTRIAL HYGIENE MICKOSCOPY 



^\ilh a phase contrast microscope. With a 

 normal microscope these fibrils are visible 

 as structureless slime. The fibers are often 

 so badly affected by pulping that they can 

 be distinguished only by staining methods. 

 The large vessels are also torn apart. Often, 

 however, the fragments of these vessels are 

 sufficient for identification. 



On the whole, soft w^ood pulp shows a 

 similar picture. Here again it is mainly the 

 occurrence of two-dimensional fibrils that 

 distinguishes them from rag fiber. As a rule, 

 soft wood fiber disintegrates more than hard 

 wood fiber. For strongly pulped specimens, 

 pieces of tracheides with the typical single 

 row bordered pits are important for identifi- 

 cation, in addition to staining methods. 



Pulping of straw and esparto fibers has 

 much less effect. Straw fibers are only very 



slightly affected (Fig. lb). Comparatively 

 slight internal fibrillation, in addition to ex- 

 ternal fibrillation of the ends of the fibers to 

 fibril bundles is the sole result, even after 

 protracted pulping. The skin cells j^how a 

 strong tendency to ci'imible, while the paren- 

 cyma cells are badly torn and pulped into 

 large pieces. Difficulties in identification are 

 hardly ever caused by pulping. 



REFERENCES 



Herzog, "Handbuch der Mikroskopischen Tech- 



nik fiir Fat^ertechnologen," Berlin, 1951. 

 Herzog, "Mikrophotographischer Atlas der Teeh- 



nisch-wichtigen Pflanzenfaser," Berlin, 1955. 

 Stoves, J. L., "Fiber Microscopj'," London, 1957. 

 Wolff, Tobler, F.v.G., "Mikroskopische Untersu- 



chung Pflanzlicher Faserstoffe," Leipzig, 



1951. 



J. ISINGS 



HiSTORADIOGRAPHY. See X-RAY MICROSCOPY 



Industrial hygiene microscopy (including refrac- 

 tive INDEX MEASUREMENT) 



The microscope is used as a qualitative 

 instrument in the field of industrial hygiene 

 to determine w'hether the type of dust preva- 

 lent in the working environment of the in- 

 dustrial worker is of a toxic nature and thus 

 may be injurious to health. Determination 

 of the amount of the toxic dust in the air is 

 also usually necessary to evaluate the degree 

 of hazard. Approximate percentages, such 

 as in the case of quartz dust, can sometimes 

 be determined with the microscope. How- 

 ever, in most instances, use of wet chemical 

 analysis or additional instrumentation such 

 as the spectrograph or x-ray diffraction is 

 also necessary for more accurate quantitative 

 results. 



Following this preliminary cjualitative and 



quantitative investigation, the microscope 

 is used for counting the number of dust 

 particles in the air and determination of 

 their particle size. Results obtained may in- 

 dicate that a definite health hazard exists. 

 For example. Threshold Limit Values 

 adopted at the yearly meetings of Govern- 

 mental Industrial Hj^gienists state that in 

 the case of dust containing more than 50% 

 free silica, the number of dust particles in 

 the breathing area of the worker should 

 not exceed five million particles per cubic 

 foot of air. This is particularly important in 

 the case of small particle size dust which 

 presents a greater health problem. Micro- 

 scopic examination indicates that in pneu- 

 moconiosis, the particle size of dust in the 



400 



