These filters are for use with the Misonix Economy Chemical Workstation part #1-4810. Hydrocarbon filters should be used if chemicals or solvents are to be used in the unit. If powders and particules are being used, a HEPA filter should be used instead. The Particulate Pre-Filters should be replaced any time a main filter HEPA or Hydrocarbon is being replaced, or in the event of low air flow through the unit.