Real-time exposure monitoring allows for a comprehensive root cause analysis that can lead to effective and cost-efficient actions to lower worker


exposures to air contaminants.


the workplace environment. Poten- tial sources of exposure include: • Transport and handling new and recycled silica sand.


• Molding and coremaking processes.


• Shakeout and handling castings following shakeout.


• Sand reclamation. • Transport, staging and remelting scrap.


• Cleaning and finishing castings. • Furnace and ladle relining. • Housekeeping. • Dust collection system maintenance. Each employee’s overall expo-


sure to indoor air contaminants is a result of the sum of exposures received directly from air contam- inant sources and those received from breathing the background air surrounding the workstation. Figure 1 graphically depicts these two different exposure modes. Source emissions can be directly controlled by local exhaust hoods, and the worker may or may not breathe these emissions prior to capture occurring. Te remaining fugitive emissions,


which are not controlled at the source by close capture exhaust hoods, dis- perse into the background air, where they remain available to inhalation and are captured by local exhaust hoods (termed secondary capture) and evacuated from the building through general exhaust fans. In the majority of root cause


analysis cases, it is recommended that two real-time dust concen- tration measurements be made simultaneously: worker exposure measurements and measurements


34 | MODERN CASTING December 2014


Fig. 2. A worker is outfitted with a real-time respirable particle monitor, with the intake located within the breathing zone and a conventional sampling pump drawing air through the monitor on the waist.


of background air concentration in the vicinity of the workstation being evaluated.


Real-Time Monitoring of Respirable Particulate Matter


A number of optical measure-


ment devices are available for use in real-time root cause evaluations. One of these instruments is shown in Fig. 2, mounted on the worker’s body for exposure monitoring. When selecting an optical


device for root cause evaluation, one should put added importance on the following qualities: • Portability—the device is


mounted easily on the worker’s body within his or her breathing zone.


• Active Sampling—pollutant- laden air is drawn through the unit using an external pump. An active sampling method results in quicker responses to changing particulate concentrations than a passive instrument can provide.


• Logging—logging functionality is essential to time synchronization with written field notes and for field calibration of the instrument. Logging frequencies down to one second are useful.


• Field Calibration—the calibra- tion of optical particle monitors is affected by particle size distribu- tion in the air being sampled. Optical devices often are factory calibrated to a standardized par- ticle size distribution, such as Ari- zona road dust having a median particulate sizing of 5 µm. Unless calibration is done based on the actual aerosols tested, larger particles such as in grinding, or smaller particles such as in weld- ing, are likely to result in skewed particle concentration results. The sample train of the monitor includes a PVC preweighed filter, which allows for calibration of real-time sample data.


Stepwise Approach to Root Cause Analysis


Step 1. Industrial hygiene exposure assessment. Efforts to control worker expo-


sures to air contaminants, including the assessment of root causes of exposure, should be preceded by a thorough industrial hygiene hazard assessment of the facility. Hazard assessment is aimed at defining workers who are at risk of being overexposed to chemical and physical hazards, including potential expo- sure to respirable crystalline silica. Measurement of exposures is an integral component of hazard assess- ment. Te first step in any root causes evaluation for silica exposure is the collection of exposure compliance samples. Tese samples are full- shift TWA samples collected using


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