Discussion and conclusions
The respiratory exposure to formaldehyde did not ex-
ceed the Finnish occupational limit value (15 min),
which is 1.2 mg/m3. The highest concentration mea-
sured, 0.81 mg/m3, accounted for 68% of the OEL15 min.
The highest mean exposure levels were detected in the
assembly and hot pressing sections of the factory by
both stationary and breathing-zone sampling. The use of
wood-preservative-containing glue (7% free formalde-
hyde) did not have any in¯uence on air concentrations.
This study demonstrates that stationary sampling
yields reasonably accurate respiratory exposure esti-
mates in the plywood industry, where the workers only
rarely leave their working stations. It seems that the
workers are exposed mainly to process-type emissions
rather than to the manual type (Kalliokoski 1990). The
emissions are due more to the process itself, and the
worker does not have much in¯uence on the situation.
The possibility of considerably higher levels of exposure
occurring due to exceptional process situations or non-
hygienic work habits of an individual worker should,
however, be given serious attention. The variation in
concentrations measured in breathing zones was greater
than the variation in stationary samples, but on average
the breathing-zone concentrations were lower. Formal-
dehyde concentrations measured in the breathing zones
of workers were divided into four task groups and then
compared with the concentrations measured in corre-
sponding areas of the factory, e.g., at the stationary site
nearest to the worker group in question (Fig. 1).
It is convenient and practical to use stationary sam-
pling. Up to a certain level the accuracy of the assessment improves with increasing sampling time. In the
collection of breathing-zone samples it is much more
dicult to prolong the measurement time. However, it
should be noted that stationary sampling is not suitable
for all exposure situations. An important part of expo-
sure assessment is careful selection of the sampling
method to be applied.