Patent ID: 7442237

Claim:
A filter for an air-purifying respirator, comprising: a filter housing having a chamber for a filter media and at least one viewing window in said housing; a sorbent filter media positioned in said filter media chamber, said sorbent filter media comprising a sorbent bed effective for gas filtration; and a plurality of colorimetric indicator elements positioned adjacent to one another within the sorbent bed and behind said at least one viewing window, wherein each of said colorimetric indicator elements is configured to display a distinct color change signal in response to detection of a predetermined level of filter penetration of a chemical threat agent or threat agent category corresponding to an end-of-service-life condition of the sorbent filter media, and wherein said indicator elements are positioned within the sorbent bed so that said indicators are exposed to and detect target agent wavefront penetration in an area inside the sorbent bed adjacent a side wall of the filter, and not at the effluent side or edges of the sorbent bed, said indicator elements comprising a sensing side and a display side, the display side positioned behind said at least one viewing window and the sensing side positioned substantially in contact with an internal area of the sorbent bed having sufficient airflow.