| Source Identification Protocol
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The following tools are useful for identifying sources of lead exposure:
| Source Identification Protocol |
Each battery manufacturing plant has literally hundreds
of sources of emission, any of which might contribute to an employee's overall daily
exposure. Limited technical and financial
resources often make
it necessary to
prioritize control needs and implement controls
in a step-wise fashion. This requires
planning so that controls can be applied on a true, "worst-case first" basis.
Therefore, a systematic evaluation of emissions, exposures, contributors to exposure,
optional controls, and costs of controls should be made prior to any attempt to install
engineering controls. This will save time, money, and provide the most cost-effective
application of controls and give the optimum control for the money spent.
The following is an inexpensive assessment procedure:
- Measure
employee exposures using 8-hour, time-weighted average, breathing zone
sampling techniques (8-hour, TWA-BZ). Standard methods for
sampling and analysis
are available.
- Conduct an emission inventory
to identify all potential emissions
in the work
environment. This inventory qualitatively identifies emission sources
that potentially contribute to employee exposure.
The second
plan view of Figure
1: Source Characterization
demonstrates the approach.
- Study
employee work practices, work locations, and air movements
to determine potential contact with emissions. See, for example, the third and fourth
plan view on
Figure
1: Source Characterization.
- Based on the available information, the industrial hygiene engineer ranks emission
sources in order of contribution to exposure. If enough information is available,
percentage contribution of emissions may also be estimated. Spot examples (short
term) may be taken to confirm the estimate.
Major data inputs to this method are:
- Employee exposure levels
- Segmented samples
- Source and area samples
- Work practices and geographical location of employee throughout shift
- Employee interviews concerning emissions, work practices, upset conditions,
machine downtime, and cleanup
- Air flow patterns in the work area (drafts and thermals)
- Appraisals of the relative importance of emission sources
- Evaluation of:
- material handling operations
- exhaust and make-up air systems
- process and product characteristics
Sample
calculation
If an employee works
seven hours stacking (average lead value from area samples: 60 µg/m3)
and one hour in the oxide plant (average lead value: 500 µg/m3), is the oxide
plant the major contributor to exposure? To "quantify" the
contribution, it is possible to calculate the expected exposure level and the
relative contribution of each major source (420 hr ×
µg/m3
vs. 500 hr. × µg/m3, or 45% from stacking and 55% from the oxide plant).
| TWA = |
(7
hrs)(60 µg/m3) +
(1 hr)(500 µg/m3)
(8 hrs) |
= 115
µg/m3 |
Now, to verify this estimate, we can imagine the monitoring records for the employee. If the average TWA exposure level is near 115 µg/m3, then we have
some evidence to support our calculations. If the actual exposure level is higher, or
lower, we should go back to the beginning and evaluate the initial assumptions (thereby
possibly identifying other sources contributing to the worker's exposure, or making an
adjustment in the initial exposure assumptions).
Having identified the major contributor, we can now make a judgment for control
(that is,
should oxide emissions be controlled? How much control of each emission source can be
achieved? What control will give the greatest reduction of lead levels versus the number
of employees exposed?).
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| Video Exposure
Monitoring |
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With video exposure monitoring (VEM), worker exposures to lead are monitored
and recorded with a direct reading instrument. At the same time, workplace activities are recorded on
a videotape. There are three examples of video exposure monitoring in this eTool.
Note: These examples illustrates the level and duration of exposure to total dust and is used to show
how VEM can be used for determining sources of employee exposure. Other sources of employee lead
exposure can be determined by using VEM sampling for a full work shift. See the Direct-Reading
Instruments Safety and Health Topic page,
the section Video Exposure
Monitoring for additional information about VEM.
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