Handbook of Solvents - George Wypych - ChemTech - Ventech!

18.4 Solvent uses with exposure risks 1255
often spend most of their time in the clean control room. Thus, the workers’ exposure levels
depend mainly on their moving pattern during the work shift. In addition, the emission rate
depends on the production rate, i.e. on the consumption rate of the solvent (toluene). Stationary
sampling can be applied for exposure assessment when it is combined with questionnaire
on use of time in various areas. This can be done with a direct-reading instrument
because the airborne concentration level remains quite stable. 20
The possible skin exposure should also be taken into consideration. If skin contamination
seems possible adequate protective clothing should be used. Glove selection is an important
but difficult issue. Glove materials often tolerate organic solvents poorly. Glove
manufacturers have useful information for selecting gloves for individual solvents. Especially
difficult is, however, to find gloves protecting efficiently penetration of solvent mixtures.
Nitrile (butadiene-acrylonitrile copolymer) gloves are often chosen in such a
situation. There is, however, considerable intermanufacturer and even batch lot variability
in penetration of solvents through nitrile gloves. 19 The workers should also be instructed not
to use thinners for hand and skin cleaning.
Total quality management (TQM) is an effective way to ensure also a high quality of
the working environment. The guidance for right and safe working practices should be subjoined
to all working instructions. Employee participation is an essential feature of a well
working TQM, and also greatly assists the achievement of the hygienic goals set.
18.4.3 PRODUCTION OF PAINTS AND PRINTING INKS
Painting technology has changed over the years. The exposure levels were generally highest
between the mid-1950’s and mid-1960’s when solvent-based paints were used extensively
both as construction and industrial paints, and exposure control technology was still undeveloped.
21 Rotogravure and silkscreen printing inks contain organic solvents. Until 1950’s
benzene was used as the solvent in rotogravure inks and it remained as an impurity in toluene
until 1960’s. 22 Today, toluene used in rotogravure inks does not contain benzene.
Alkoxyalcohols and their acetates are used as silkscreen ink solvents. The development of
safer solvents has been started quite recently. First, alkoxyethanols were replaced by their
acetates which have lower vapor pressures. This did not, however, improve the safety much
because the skin is the main route of absorption for both alkoxyethanols and
alkoxyethylacetates, and they are considered to be equally toxic. Their substitution by
alkoxypropanols and their acetates is, however, a significant improvement because those do
not metabolize to toxic alkoxyacetic acids. 23
High exposures remained common in paint and printing ink industry still in 1970’s;
for example, most solvent measurements conducted in these industries in Finland exceeded
the present OELs. 24 Water-based paints are today clearly most common in construction
painting. Alkyd-based construction paints with white spirit (Stoddard solvent, mineral spirit
or solvent naphtha) as a solvent are, however, still produced. Solvent-based paints have remained
most common in industrial painting, even though the solventless powder paints are
also produced in large quantities.
The main products are nowadays manufactured in automated processes. On the other
hand, special products are also usually made in batches and include several manual tasks. In
addition to paints and inks, thinners are often canned. When the processes are provided with
proper enclosures and local exhausts, the airborne solvent concentrations can be kept well
below the OELs. An easy but important control measure is to keep all solvent containing
pots covered. Xylene (TLV 100 ppm, the Finnish OEL 100 ppm with skin notation), toluene