Exposure indicating apparatus
 An exposure indicating apparatus for monitoring air flowing along a flow-through path extending from the external environment through an air purifying respirator cartridge and into a face mask. A processor housing is releasably attached to the flow-through path so that it can be removed allowing ambient air to enter the flow-through path at the attachment location. A reversible sensor with at least one property responsive to a concentration of a target species within an environment is in fluid communication with the flow-through path. A processing device in the processor housing generates a concentration signal as a function of the at least one property of the reversible sensor. An indicator provides an active indication in response to the concentration signal. A flow-through housing may form a portion of the flow-through path. The flow-through housing may be interposed between the air purifying cartridge and the face mask. The reversible sensor may be located in the processor housing, the air purifying respirator cartridge or the flow-through housing. The sensor is coupled to the processing device by a coupler. 
Minnesota Mining and Manufacturing Company
A
A62B
inventional
Edward E. Mark K. Richard J. Gregory Lowell R.
Parsonage Debe Poirier Yuschak Miller