> There should be a plastic cover on the cartridge. This cover comes off
> (probably the lever in the diagram) The prefilter goes on the cartridge
> and them the cover goes on to hold it in place. The prefilters stop the
> dust particles from clogging the cartridge before the charcoal has been
> used up.

> Ian

I kind of figured that but there isn't a lever to open the cartridge, and when I pry on the plastic cover It seems like its going to break rather than come off does anyone know the trick? the cartridge is for organic vapors from 3m.