Page 368 - Industrial Ventilation Design Guidebook

5.3 TOXICITY AND RISKS INDUCED BY OCCUPATIONAL EXPOSURE TO CHEMICAL COMPOUNDS 323

local exhausts cannot be used generally, the ventilation may depend on the
possibility of keeping the doors and windows open. Breathing zone sam-
ples are collected during painting of doors, window frames, floors, walls,
etc. in rooms of different size (e.g., small, medium, and large), both with
doors and windows open and with them closed. The time use distribution
can be obtained with a questionnaire.
In process industries, the areal distribution of airborne pollutant con-
centrations becomes important. Thus, workers' exposure levels depend
on their movement patterns during the working day. Ideally, the pro-
cesses are closed, but, in practice, in-plant emissions occur from openings
needed for material flows and sampling. Sometimes, in-plant emissions
are intentionally allowed to be discharged into workroom air in areas
where workers do not spend any time. In addition, fugitive emissions
commonly take place due to leaking seals in flanges, valves, pumps, and
fans. For continuous processes, the time variation of airborne concentra-
tion often depends predominantly on relatively few process parameters,
such as production rate, temperature, and pressure. These are also im-
portant for batch processes, but there are usually certain process phases
during which the emissions are heaviest. Batch processes generally also
include several manual tasks, such as emptying sacks and barrels.
Since the concentration gradients are not very steep at the actual
working areas, it is more convenient to use stationary monitoring instead
of personal sampling, and ask how much time, on average, each worker
spends in various areas. Direct reading instruments provided with a
multi-point sampling system are especially useful because they permit
long-term concentration follow-up without excessive costs. Even though
accurate information on time use cannot be obtained with questionnaires
or interviews, and the coverage of stationary sampling points remains in-
complete, the error due to these inadequacies is, nevertheless, usually
much smaller than that caused by too brief a sampling time in personal
monitoring. In addition, relationships between process parameters and
airborne concentrations may be identified. This allows the assessment of
long-term exposure because long-term statistics of the important process
parameters are usually available. In industries using batch processes, the
concentration variation during various process phases should also taken
into consideration. Figure 5.53 shows the linear relationship between air-
borne toluene concentration and toluene concentration observed at sta-
tionary sampling sites in a printing plant. The annual average
concentration is now obtained for each monitoring site simply from the
point on the line corresponding to the average use of toluene during the
year. 195

5.3.5.2 Biological Monitoring
While occupational hygiene measurements always measure only the con-
centrations of chemical compounds present in the occupational environment,
i.e., the potential dose, the analysis of biological specimens predominantly re-
flects the body burden. Furthermore, biological monitoring is always limited
to assessment of individual exposure. Personal occupational hygiene sampling
takes into consideration only some of the individual factors, e.g., working