Another problem occurs when a screen cover is lifted during operation to clean the screen
surface. This basically renders the LEV system ineffective because the increased area with the
cover lifted is so great that the screen area is not able to be kept under negative pressure. This is
a known problem throughout the industry. The only safety option currently available to workers
when performing this task is to wear fit-tested personal protective equipment (PPE) that is rated
for the levels and type of dust being processed