Student Research: Patrick Moore

, , 1998
Faculty Advisor: Noah S. Seixas

An Assessment of Occupational Exposure to Respirable Particulates and Sulfur Dioxide During Aluminum Smelter Potroom Operations


Several health hazards associated with the primary aluminum reduction industry have been recognized, lung and bladder cancer has been associated with exposure to coal tar pitch volatiles in some processes. Some researchers have linked the gas, fume, and dust exposures found in aluminum smelter pot rooms with the incidence of bronchitis and asthma. The exact cause of this potroom asthma and the risk factors involved remain poorly understood despite substantial clinical and epidemiologic investigation.

As part of a prospective inception cohort study of respiratory symptoms and airway reactivity, an assessment of the short-term and full-shift particulate and sulfur dioxide exposures of twenty workers in an aluminum smelter potroom was undertaken. Short-term exposures were investigated since some researchers believe that the potroom asthma may be an irritant reaction to short-term high exposure to a respiratory irritant that is found in the potroom. A real-time continuous aerosol monitor was used with a data logger to measure and store the continuous aerosol exposure. A filter was used in-line to measure average particle and fluoride exposures. Due to the loss of particles along the length of the sample tubing, particulate exposures are expressed as pDR units instead of in mg/m3. As such, they do not directly represent actual particulate concentrations in the breathing zone, but instead are relative concentrations. Sulfur dioxide exposures were measured on a real-time basis using a toxic-gas monitor with an electrochemical sensor having an internal data logger. While real-tie exposure monitoring was taking place the work activities of each participant were also recorded for analysis purposes.

The main findings of the this exposure assessment study were:
1) Particulate fluorides accounted for 25% of the total particulate matter collected, while gaseous hydrogen fluoride made up 31% of the total fluoride concentration. Fluoride exposures, both particulate and gaseous, are one of the most prominently mentioned agents that could be involved with adverse respiratory ailments, including asthma, within potroom workers.
2) The type of job, work location, activity, and specific task that the potroom workers were involved with had a major effect upon the particulate and SO2 concentrations to which they were exposed. Evaluation of particulate and SO2 exposures and work place variables suggest that work location and activity has the greatest effect on work place exposures followed by task and job title. Generally, it was found that the variability of SO2 exposures were greater than those of particulate exposures. This is due to the fact that particulate exposures are more uniform throughout the potroom environment, while SO2 exposures are directly related to the workers proximity to an aluminum pot. Basically, correlation between particulates and SO2 exposures were elevated such as when working over a covered pot, or when both types of exposures were low such as while located outside the potroom. The largest contribution to the total variance in exposures came from within-day variability, suggesting that a primary control strategy should focus on limiting a worker's exposure by controlling high exposure tasks that occur on a daily basis, such as anode changing and covering anodes with ore.
3) That workers are exposed to short-term elevated levels of respiratory irritants during certain jobs, work locations, activities, and tasks. Data analysis was performed to examine when workers were exposed to concentrations of particulates and SO2 above the OSHA PELs. When performing activities that involve working on an aluminum pot particulate exposures were elevated 11 to 39% of the time, compared to 4 to 7% of the time when working in other parts of the potroom. When working on a pot SO2 exposures were elevated 0 to 12%, compared to less than 1% in other areas of the potroom.
4) That the present use of respirators by the potroom workers should be fairly effective at protecting them from these short-term elevated exposures to respiratory irritants. When working over an uncovered pot, where the majority of particulate and SO2 exposures take place, workers were found to be wearing their respirators over 98% of the time. However, there are other areas within the potroom where workers can receive elevated exposures where their use of respiratory protection is not as complete. Another problem is that workers are donning and doffing their respirators numerous times during the carbon exchange process, which means that the respirators may not be providing the expected respiratory protection needed.