Abstract: A calibrateable light ray scattering reference rod utilized in a light scattering dust monitor. This light ray rod scatters an amount of light equivalent to a given concentration of dust. Adjustability is provided so that several concentrations of dust can be represented. This adjustment is accomplished by moving a threaded opaque slug axially inside the translucent rod.

Abstract: A filter assembly (10) for the filtration of toxic gases from the air is disclosed, which includes a unitized cylindrical housing having oppositely disposed end covers (11, 12), with an inlet port (11a) in one end cover and an outlet port (13a) in the side wall. An annular, pleated filter element (21) extends between the end covers (11, 12) between perforated liners (18, 19), and a third, perforated liner (20) is spaced outwardly from the center or common liner (19) to provide an annular space therebetween which is filled with activated charcoal (27). Fines media (25, 26) are positioned on opposite sides of the activated charcoal (27). The first, pleated filter (21) and the second, charcoal filter (27) are thus mounted contiguous to one another on opposite sides of separating wall (19, 25), and extend between the end covers (11, 12) to provide filtration for air being drawn through the filter unit.