Abstract: The problems of non-uniform treatment of paper pulp that may be caused by differential flow velocities within a vessel, channeling, and/or disruption of the pulp flow, are substantially eliminated by providing a non-circular cross-section substantially atmospheric pressure vessel with at least one screen surface, and typically a liquid introducing device. The vessel, screen surface, and liquid introducing device are constructed and positioned with respect to each other so that during the treatment of a pulp slurry the slurry has substantially uniform width in a treatment zone, and there is substantially uniform resistance to the flow of slurry over the screen surface over any particular cross-section of the vessel in the treatment zone, and its consistency varies less than 6% in the treatment zone (e.g. between 8-14%).

Abstract: In asbestos abatement or decontamination work, negative pressure is established within a work area, and air entering the work area in response to the negative pressure is caused to pass through or past a HEPA filter in an air inlet to the work area. If the negative pressure within the work area ceases, as in an emergency situation, any air exiting the work area through the air inlet is caused to pass through the HEPA filter. This may be accomplished by pivotally mounting the HEPA filter for rotation about a horizontal axis so that it moves out of the way of inflowing air, while outgoing air must pass through the filter.