Respirator cartridge end-of-service lift indicator system and method of making

Providing visual means for indicating when vapor/gas respirator cartridges have exhausted their capacity to provide respiratory protection at or below a hazardous concentration level. In combination with a vapor/gas indicator adapted to undergo a change in color with contact by an organic vapor or gas, there is provided a catalytic agent for enhancing activation and reaction of the indicator agent.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to respirator cartridges with particular reference 
to improvements in means and method for indicating end-of-service life of 
organic vapor/gas respirator cartridges. 
2. Discussion of the Prior Art 
Respirators of the type employing replaceable filter cartridges are 
commonly used for protection against a wide range of respiratory hazards 
which include toxic and disease producing dusts, mists, sprays, fumes, 
vapors and gases. The cartridges are replaced when their capacity to 
provide respiratory protection at or below hazardous concentration levels 
becomes apparent to the user or is otherwise arbitrarily or 
administratively determined. 
Detection of cartridge exhaustion by a user's taste or smell of potentially 
hazardous fumes or gases coming through the cartridge or a resistance to 
his normal breathing due to clogging with dust may provide adequate 
protection against the danger of using spent cartridges in cases where the 
respiratory hazards are, for example, ammonia fumes, acidic and alkaline 
gases or certain dusts which produce odors, tastes and/or breathing 
resistances which are detectable before reaching hazardous concentrations. 
Protection against organic vapors or gases which have no such warning 
properties, however, presents a much more serious problem which heretofore 
has required administrative control of cartridge use, i.e. its time of 
replacement being determined according to type and degree of toxicity of 
the hazard, its immediate concentration, the humidity at the sight and 
corollary environmental conditions. Variations in one or more of the 
aforesaid factors and their corrollaries during use of a particular 
cartridge can cause serious problems if not detected and, least of all, 
complicate end-of-service life calculations. 
There are in the art a number of windowed respiratory cartridges or 
cannisters having color changing indicator means therewithin which 
allegedly afford indication of residual useful life and/or impending 
exhausting of the cartridges or cannisters. U.S. Pat. Nos. 1,537,519 and 
3,966,440 are exemplary. These devices, however, involve the use of 
indicators supported by thin and/or opaque carriers such as strips of 
paper, activated alumina or the cartridge sorbent itself so that only the 
portion of the indicator against the window is visible. 
The use of a porous translucent carrier for cartridge end-of-service life 
indicators which permits viewing thereinto for perception of a substantial 
depth of an indicator has been suggested in an application for patent 
filed January 5, 1977 and having Ser. No. 757,105, now abandoned. 
While this provides an important advance in the art, i.e. by affording a 
more readily visible and reliable cartridge end-of-service life 
indication, there remains a need for still greater sensitivity to 
cartridge sorbent exhaustion, i.e. a more dramatic or vivid display of 
end-of-service life indication. 
Accordingly, a principal object of this invention is to afford novel means 
and method for enhancing the color changing activity and general display 
function of gas oxidizable color indicators used in windowed or otherwise 
transparent respirator cartridges. 
A corollary object is to enhance oxidation and color change of 
end-of-service life indicating means by catalytic action and/or 
preconditioning of vapors and gases reaching the indicating means. 
Other objects and advantages of the invention will become more readily 
apparent from the following description. 
SUMMARY OF THE INVENTION 
In a gas/vapor sorbent-containing respirator cannister or cartridge having 
window means and a toxic gas/vapor oxidizable end-of-service life color 
indicator visible therethrough, the present invention includes an upstream 
catalytic/oxidizing agent for enhancing action of the color indicator. The 
agent is so positioned and formulated as to receive and oxidize a vapor or 
gas into a product more readily detected by the cartridge indicator and/or 
to so activate the gas or vapor that it can be more easily oxidized and 
detected by the indicator. 
It is to be understood that the aforesaid window means may include any 
portion or all of the cartridge shell, the cartridge sorbent may comprise 
activated charcoal or other conventional means and use of the expression 
catalyst herein is to be interpreted in its broadest sense as meaning a 
substance that initiates a reaction enabling procedure under milder 
conditions than otherwise possible.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
According to the invention there is provided in a transparent organic 
vapor/gas respirator cartridge 10 having an end-of-service life indicator 
12 and a catalytic oxidizing agent, hereinafter referred to as catalyst 
14, located adjacent indicator 12 in a position upstream thereof. As 
indicated by arrows 16 (FIG. 2) the stream of air and gases and/or vapors 
through cartridge 10 when in use passes into and through its perforated 
end 18, sorbent 20 and outwardly of perforated end 22. Thus, with 
indicator 12 and catalyst 14 supported in a compartmented perforated 
container 24, the portion of airstream 16 adjacent container 24 is caused 
to first enter catalyst 14 and then pass into indicator 12 prior to 
proceeding downstream through end 22 as illustrated with arrow 26. 
It is to be understood that the construction of cartridge 10 as depicted in 
FIGS. 1 and 2 has been selected for purposes of illustrating principles of 
the invention only and that various other forms of respirator cartridge 
and/or cannister designs and constructions may be used within the scope of 
the invention. For example, cartridge 10 including the illustrated 
transparent shell 28 and perforated end covers 18 and 22 may be formed of 
metal such as aluminum or opaque plastic materials and provided with 
transparent window means for visual perception of indicator 12. Such 
window means having been illustrated in copending application Ser. NO. 
757,105 will not be shown or further described herein. The cartridge 
sorbent 20, e.g. activated charcoal, is prevented from escaping through 
perforations in end covers 18 and 22 by liners 29 and 30 of felt, woven 
fabric or suitable screening. 
Catalyst 14 is fabricated as follows: 
(1) Measure 50 grams of granular petroleum base activated carbon. 
(2) Prepare impregnating solution: a. 200 ml H.sub.2 O (distilled) 
b. add 30 (.+-.20) grams Na.sub.2 CR.sub.2 O.sub.7 and dissolve 
c. add 30 (+32, -15) ml of reagent or technical grade concentrated H.sub.2 
SO.sub.4 and allow to cool. 
(3) Pour carbon into solution (2) and permit to stand for sufficient time 
to accomplish total saturation, e.g. one hour. 
(4) Decant remaining liquid from carbon and allow carbon to dry, e.g. 3 
hours at a temperature of from 150.degree. F. to 250.degree. F. in an 
air-circulating oven. 
Note: The carbon reduces the impregnating solution and functions as its 
carrier. 
Modifications of the foregoing fabrication procedure are: 
A. Delete (c) in step (2) and proceed to step (3). 
B. Delete (c) in step (2) and add 30 (.+-.5) grams FeCl.sub.3 and proceed 
to step (3). 
C. In (b) of step (2) use approximately 10 grams Na.sub.2 CR.sub.2 O.sub.7, 
in (c) of step (2) use approximately 10 ml H.sub.2 SO.sub.4 and add 10 
(.+-.5) grams FeCl.sub.3 and 5 (.+-.2) grams ZnO. Mix the foregoing in any 
order but with H.sub.2 SO.sub.4 added last. 
D. Add 40 (.+-.20) ml of commercial grade granular silica gel to the sodium 
dichromate decantate of step (4), this is reduced sodium dichromate. 
Permit the silica gel to stand in the reduced sodium dichromate solution 
for a period of time sufficient to accomplish total saturation. 
One hour will produce satisfactory results. 
Decant excess liquid from the silica gel and dry, e.g. two to four hours at 
from 150.degree. F. to 250.degree. F. Three hours at 225.degree. F. has 
demonstrated desirable results. 
With one or another of the foregoing reduced sodium chromate catalysts 
carried by either the activated carbon or silica gel and placed upstream 
of indicator 12 as illustrated, enhanced activation and intensification of 
the display of color of indicator 12 is accomplished for improved 
end-of-service life indication. 
A desirable indicator 12 may consist of a solution of a reagent grade 
sodium dichromate in sulfuric acid and water supported by granular silica 
gel. The solution is added to the silica gel and dried in place. Those 
interested in details of such indicators may refer to copending U.S. 
Application Serial No. 757,105. 
It should be apparent from the foregoing that the indicator system of the 
present invention is readily adaptable to various types and/or forms of 
respirator cartridges or cannisters other than that illustrated in the 
present drawings. Various modifications and adaptations of the precise 
mechanical and chemical forms of the invention here shown and described 
may be made to suit particular requirements, e.g. agents other than the 
above-described activated carbon may be used to reduce the sodium 
dichromate solution. Formaldehyde and hydrogen peroxide are examples. The 
foregoing illustrations are not to be interpreted as restrictive of the 
invention beyond that necessitated by the following claims.