Service life indicator for respirator cartridge

A respirator cartridge comprising:

• a cartridge shell having a sidewall, at least a portion of which sidewall is transparent;
• a chemical sensor having a color-changing display field, the sensor being securely positioned proximate an interior surface of a transparent portion of the cartridge sidewall, said display field having an upstream end and a downstream end;
• a display window defined by an opaque border positioned on the transparent portion of the cartridge sidewall, the display window being at least partially aligned with the display field of the sensor, the downstream end of the display field of the sensor extending to the downstream end of the display window formed by the opaque border;
• a chemical sorbent material contained by said cartridge shell and in touching contact with said sensor;
• said cartridge further comprising:
• an outwardly extending mounting collar joined to the cartridge shell, said mounting collar including seal-forming means,
• a threaded flange member having pawl and seal-forming means received in mating relation with said mounting collar,
• ratchet means formed in a surface of the cartridge shell to operatively engage the pawl means in the flange member, where said seal-forming means comprise an annular ring and a corresponding annular seat, whereby said flange member is securely joined to said cartridge shell in fluid-tight rotatable relation.