INDICATOR FOR RESPIRATOR FILTERS
This application claims priority from U.S. Provisional Application Ser. No. 60/610,868, filed Sep. 16, 2004.
The invention described herein may be manufactured, licensed, and used by or for the U.S. Government.
The present invention relates in general to monitoring the status of air-purifying filter systems, and more particularly to a system and method for indicating the service-life remaining for a multiple threat agent respirator filter in an air-purifying respirator, and like apparatus.
Modern air-purifying respirators targeted to filter a range of threat agents, such as chemical, biological, radiological and nuclear (CBRN) respirators, rely on filter elements that have limited service lives. While these respirators are intended to be worn for protection against threat agent airborne concentrations that are dangerous to life and health, presently, the respirators provide no direct indication of their remaining gas-life capacity. Current military doctrine for determining how often to exchange CBRN mask filters is therefore based on evaluating factors calculated to indirectly indicate the remaining gas life, such as the physical condition of the filter, the type and extent of threat agent exposure, climatic conditions, and other criteria that are known to affect service life. The uncertain and subjective nature of these factors and the consequences of miscalculation have lead to widespread premature disposal of filters. For example, according to military doctrine, during wartime operations, respirator filters in masks that have been worn in areas previously exposed to a chemical attack are to be disposed of after 30 days. In actual practice, however, the respirator filters are often exchanged in a combat environment every 30 days whether or not there has been a confirmed chemical attack. These change-out practices, of course, are deliberately conservative but they impose substantial additional costs and logistic burdens on military and civilian authorities responsible for maintaining an adequate supply of replacement filters. Even conservative filter change-out practices provide no absolute assurance that a respirator filter is still effective.
Military and emergency responder communities including security and law enforcement personnel, tactical response units, health care workers, and a growing number of other users require a more reliable and objective means to determine when to replace a CBRN filter. Embodiments according to the present invention address these concerns, at least in part.
In general, in one aspect, an embodiment of a calorimetric display for signaling an end of service life condition for a multi-agent air-purifying respirator filter according to the present invention, includes a number of adjacent colorimetric indicator elements, each element configured to produce a distinct color change in response to detection of a predetermined level of penetration through a sorbent filter media of the respirator filter of a distinct chemical threat agent or threat agent category.
In general, in another aspect, an embodiment of a colorimetric indicator according to the present invention includes a substrate coated with a reactive chemical compound that produces an indication comprising a distinct color change in
5 response to detection of a CBRN target chemical threat agent, a mask overlay substantially conforming in color to the substrate before a colorimetric reaction has occurred, that selectively displays a region of the substrate configured to change color at a predetermined level of exposure to the target chemi
10 cal threat agent; and a protective backing that is permeable by the target chemical threat agent or threat agent category. In another aspect, the reactive chemical compound is selected from a group that essentially includes of Cu(TPP), Metanil yellow (3-(4-Anilinophenylazo)benzenesulfonic acid)
15 monosodium salt, Rosolic acid (basic form), Bromocresol green (acid), Congo Red (1-Napthalensulfonic acid), Zn(TPP) and Bromocresol purple (acid).
In yet another aspect, a method for displaying an end of service life signal for a sorbent filter media housed in a filter
20 element of a respirator for filtering a number of CBRN threat agents includes positioning a number of chemically reactive calorimetric indicator elements in contact with the sorbent filter media, configuring each colorimetric indicator element to display a distinct color change signal in response to detec
25 tion of a distinct chemical threat agent or threat agent category, providing at least one window integrated into the filter element housing for viewing signals produced by the plurality of chemically reactive calorimetric indicator elements, calibrating the colorimetric indicator elements to display signals
30 corresponding to predetermined maximum levels of filter penetration by the distinct chemical threat agent or threat agent category; and formatting the display of color change signals to produce one or more patterns, shapes or symbols.
35 BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a front perspective view of an embodiment of a multi-threat-agent multi-detector colorimetric ESLI in a threaded CBRN respirator filter according to the present 40 invention.
FIG. 2 shows a front perspective view of the inside of the filter housing of the threaded CBRN respirator filter illustrated in FIG. 1.
FIG. 3 shows a front perspective view of an embodiment of 45 a multi-threat-agent multi-detector calorimetric ESLI in a snap-in low profile "bayonet"-type CBRN respirator filter according to the present invention.
FIG. 4 shows a front perspective view of the inside of the filter housing of the snap-in low profile "bayonet"-type 50 CBRN respirator filter illustrated in FIG. 3.
FIG. 5 shows an exploded view of component layers of a calorimetric indicator according to an embodiment of the present invention.
FIG. 6 shows a cross-section view of the threaded CBRN 55 respirator filter illustrated in FIGS. 1 and 2.
FIG. 7 shows a cross sectional broken view of the "bayonet"-type CBRN respirator filter illustrated in FIGS. 3 and 4.
In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention, as claimed, may be practiced. This 65 invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth; rather, these embodiments are provided so