Page 414 - Industrial Ventilation Design Guidebook

6,2 OCCUPATIONAL EXPOSURE LIMIT VALUES 369

• Patterns of contaminant generation that change with time
• Interaction among several release points
• Worker variability in relation to location and time
This implies, for example, that measurements taken over a given period of
time may give insufficient data to integrate workplace factors in the series of
activities in the period under consideration in such a way as to permit assess-
ment of the likely maximum risk to which the individual workers are exposed.
The occupational exposure assessment (OEA) should take into account
the future working conditions for the employee, which implies some degree of
uncertainty, especially if the exposure is close to the limit value. Therefore, the
initial assessment of exposure may require periodic measurements to check for
any change in exposure conditions that may increase the risk to workers—for
example, if there has been a significant change in working conditions caused
by the introduction of a new industrial process or technology or new chemical
agents, which could make the risk assessment out of date. In the case of a new
risk-involving activity, work could commence only after an assessment of the
risk of such activity has been made and any identified preventive measures
have been implemented.

6.2.4.1 Procedure for Evaluation of Exposure
The standardized procedure for evaluation of exposure to chemical agents
is done in three steps:

• Identification of potential exposure
• Determination of workplace factors
• Assessment of exposure
The first step is to identify the substances present at the workplace. As a
starting point, knowledge of the process is needed in order to formulate a list
of all chemical agents used in the establishment. The list should include not
only primary products but also intermediate and final products, as well as re-
action products and by-products. For the chemical agents in the list, it is nec-
essary to know their chemical properties, especially hazardous ones; their
OEL values, including biological limit values; and, where these are not avail-
able, other technical criteria that can be used to evaluate the risk. It is also
helpful to include any information on the safety and health risks of those sub-
stances provided by the supplier or other readily available sources. This infor-
mation on dangerous substances and preparations, in the form of safety data
sheets, is intended primarily for industrial users, to enable them to take the
measures necessary to ensure the safety and health of workers.
The next step is the determination of workplace factors that have to be
considered in estimating the potential for exposure to chemical agents. This
includes all points related to work processes and procedures which may be rel-
evant to exposure, such as
• Operations, technical installations, and processes
• Emission sources
• Job functions and activities of each worker
• Work patterns and techniques
• Process layout and workplace configuration