Chemical Contaminant Measurement in the Workplace
Chemical Contaminant Measurement Methods
Direct and Indirect Measurement
The measurement of chemical contaminants in a job can be performed using the following general methods:
- Direct Measurement: This involves using direct-reading instruments in the workplace to obtain immediate, in situ results.
- Indirect Measurement: This method involves collecting test samples and using pollutant sensors for analysis.
Static vs. Personal Measurements
There are two main types of measurements:
- Static Measurements: These are based on determining concentrations in specific work areas, representative of the general environment.
- Personal Measurements: These are performed in the worker’s breathing zone.
Assessing Workplace Exposure
Personal measurements are preferred for assessing workplace exposure to chemical contaminants. This is because they provide a more accurate picture of the actual exposure experienced by the worker throughout their workday. Workers may perform various tasks that expose them to different pollutants at varying concentrations.
Direct Reading Systems for Pollutants
Extent of the Method
This method involves using direct-reading instruments to determine the concentration of a contaminant at the moment of reading.
Advantages and Disadvantages
Advantages:
- Fast determinations
- Immediate sampling at points of interest
- Economical
- Easy to handle (although interpretation requires specialization)
Disadvantages:
- Low accuracy
- Frequent interference that can distort results
Instruments for Direct Measurement
Gases and Vapors:
- Colorimetric tubes
- Non-colorimetric instruments (monitors)
Aerosols:
- Optical instruments
- Electrical instruments
- Piezoelectric monitors
Colorimetric Tubes
Colorimetric tubes are glass tubes filled with a porous material (e.g., silica gel) impregnated with a chemical reagent that produces a characteristic color stain. Contaminated air is passed through the tube using a manual vacuum pump. The length of the stain indicates the pollutant concentration (ppm or % by volume of air).
Applications
Colorimetric tubes are used for direct measurement of gases and vapors, particularly for short-term exposure measurements.
Limitations
The hygienic assessment using colorimetric tubes is not recommended due to:
- Unreliability in measurements and reading the graduated scale.
- Low specificity of the chemical reaction, which can be altered by other pollutants (interference), temperature, and relative humidity.
Monitors
Monitors for measuring gases and aerosols are based on the principle of early detection using various physical or chemical methods to quantify pollutants.