Dust Control Handbook for Industrial Minerals Mining and Processing

CHAPTER 8: CONTROLS FOR SECONDARY SOURCESThis chapter discusses various types of secondary dust sources frequently found in mineralprocessing facilities and that may have a significant impact on workers' respirable dust exposure.In some cases, the worker's personal respirable dust exposure can be more significant from thesesecondary sources than from the exposure resulting from the worker's primary job function.Because of this, these dust sources need to be recognized, identified, and controlled. Not onlydoes this chapter identify these sources, but it provides methods and techniques that are availableto minimize dust exposure from these sources.CLEANING DUST FROM SOILED WORK CLOTHESA significant area of respirable dust exposure to workers at mineral processing operations is fromcontaminated work clothing. It has been documented that the level of contamination from dustladenwork clothes was so significant in some cases that it caused a ten-fold increase in aworker's respirable dust exposure [USBM 1986]. It must be noted also that once clothingbecomes contaminated, it is a continual source of dust exposure until being changed or cleaned.One option that operations can use to deal with contaminated work clothing is to use dustblockingcoveralls that can be worn by workers. The coveralls can be removed before theworker enters a clean room/area, then discarded at the end of the shift to minimize dust beingtransferred to the worker's personal clothing. These types of coveralls are also very popularwhen dealing with different types of toxic dusts. One drawback with these coveralls is that theybecome uncomfortable for workers because they do not dissipate heat very well and a secondaryconsideration is the cost.Currently in the United States, the only Mine Safety and Health Administration-approved(MSHA) method for cleaning work clothes requires the use of a HEPA-filter vacuuming system,which makes the clothes cleaning effort both time-consuming and unlikely to be performedeffectively. It is very difficult for a worker to effectively vacuum his/her clothing, particularly inhard-to-reach areas such as the legs and back.The use of compressed air to remove dust from work clothing is prohibited by MSHA; however,because the vacuuming method is very time-consuming and ineffective, workers may attempt touse this illegal method of a single compressed air hose to blow the dust from their clothing.Although this is a slightly more effective cleaning method than the vacuuming technique, it isalso time consuming and equally as difficult to clean the same hard-to-reach areas. The primaryconcern with the blowing technique is that it creates a dust cloud, elevating respirable dust levelsfor both the worker and coworkers in the work environment [Pollock et al. 2005].Once a worker's clothing becomes contaminated, dust is continually emitted from the material asthe worker performs his/her normal work activities. Given this problem and the reality thatworkers can be exposed to multiple dust sources throughout the day, the most effective solutionis to change the contaminated clothing. Although disposable coveralls have been in use forControls for Secondary Sources 201