Note: Descriptions are shown in the official language in which they were submitted.
Field of the Invention
This inventlon relates to improvements in respirator
cartridges with particular reference to means and method for
indicating end-of-service life of organic vapor~gas respirator
cartridges.
Summar~ of the Invention
Broadly speaking the present invention provides the
method of indicating end-of-service life of an organic vapor/
gas respirator cartridge having a shell containing an organic
vapor/gas sorbent comprising: placing within the shell and
adjacent the sorbent an indicator incorporating an organic ..
vapor/gas oxidizing agent supported in a substantial depth of
a translucent carrier, the agent being characterized to undergo
a drastic change in color concomitant with exposure to con-
c~ntrations of organic vapors and gases substantially below a
threshold limit value known to be safe to inhale; and arranging
for the indicator to be visible from outside the cartridge shell
whereby perception of the drastic change in color of the indicator
may be taken as indication of end-of-service life of the
respirator cartrldge.
~ he above method may be carried out by providing a
respirator cartridge having a shell including perforated bottom
and co~er sections and a wall extending therebetween, the bottom
and cover sections permitting passage of air and gases through .:
the shell, and an organic vapor/gas sorbent within the shell
between the bottom and cover for purif~ing the air and gases
passing through the shell wherein the improvement comprises:
an organic vapor/gas oxidizing indicator agent characte.rized to
undergo drastic change in color concomitant with exposure to
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concentra-tions of organic vapors and gases which are sub-
stantially below a threshold limit value known to be safe to
inhale; a -translucent carrier of substantial depth Eor supporti.ng
the indicator agent, the carrier being porous and the agent being
supported therewithin, the carrier with inclicator agent being
disposed internally of the shell against the wall and surrounded
by the sorbent for exposure to organic vapors and gases not
absorbed by the sorbent; means for restraining the carrier
against appreciable mixing with the sorbent; and window means in
the shell through which the indicator agent may be viewed into
the depth of the translucent carrier for ready perception of an
incidence of color change of the agent and indication of an
existing condition of exposure of the indicator agent to the
unsafe concentrations of organic vapors and gases.
Thus, the present invention provides, in an organic
vapor/gas respirator cartridge, visual.indicator means for
determining when the cartridge has exhausted its capacity to
provide respiratory protection at or below a ha~ar concentration
le~el. The indicator comprises an organic vapor/gas oxidizing
agent which undergoes a color change concomitant with exhaustion
of the cartridge $orbent. The oxidizing agent is supported by
a porous translucent carrier, e.g. granular silica gel.
One or more windows are provided in the cartridge
shell against which the carrier with its oxid.izing agent is
placed for ease of observation and is otherwise surrounded by
the usual organic vapor~gas sorbent, e.g. activated carbon.
With formulation of the indicator being such that its
color change is drastic and concomitant with the organic vapor/
gas sorbency of the respirator cartridge at a point where
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effluent air contains a concentration of the vapor or gas at
or above an acceptable threshold limit value (TLV), perception
of the color change through the window indicates cartridge
exhaustion, i.e. end-of-service life.
This ability to visually indicate a condition of low
concentration o:E o.rganic vapors or gases in a cartridge effluent
affords a positive and dependable method of indicati.ng ca.rtridge
exhaustion. It overcomes the need for complicated time-
consuming and less than.optimally,.reliable conventional
administra-tive
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control procedures, their uncertainties and/or those of
other presently practiced approaches to the problem~
Details of the invention will become more readily
apparent from the following description when taken in con-
junction with the accompanying drawings.
IN THE DRA~INGS
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Fiy. 1 is a side elevational view of an organic
vapox/gas respirator cartridge embodying an end-of-service
indicator system according to the invention;
Fig. 2 is an enlarged cross-sec~ional view of the
cartridge taken generally along line 2-2 of Fig. 1, and
Fig. 3 is a fragmentary cross-sectional view taken
from the position of line 3-3 in Fig. 2 and looking in the
direction of the arrows~
DESCRIPTION O~ THE PREFERRED EMBODIMENTS
The present invention provides/ in an organic vapor/
gas respirator cartridge 10, an indicator 12 which may be used
to determine end-of-service life of the cartridge.
The indicator 12 comprises an organic vapor/gas
20. oxidizing agent suppor-ted by a poxous translucent carrier 14
of, or~example, granular silica gel and undergoes a color
change concomi-tant with exhaustion of the cartridge sorbent 16
which may, for example, comprise the customary activated gran-
ular carbon. The oxidizing agent being, for example, a dried
solution of sodium dichromate/ water and sulfuric acid deposit-
ed upon and throughout th~ porous carrier 14 cannot be illus-
trated in the drawings and, accordingly, the granular carrier
14 will be hereinafter referred to as indicator 14, .it being
understood that a color change of the oxidizing agent will be
perceived as a change of color of the translucent granular
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carrier.
In a preferred embodiment of the invention, a
conventional respirator car-tridge shell 18 is provided with
one or more apertures 20~ each covered :internally or ex-
ternally as illustrated with a transparent window 22
which, in its simplest form may comprise a strip of heavy-
duty transparent plastic tape.
Behind each window 22 J i.e. internally of shell
18, and fixed to shell 18 is a foraminous barrier 24 of
fine mesh plastic or metallic screen functioning to res-
train indicator 14 in the illustrated position adjacent
window 22 for viewing before, duxing and/or after use of
cartridge 10. The usual organic vapor/gas sorbent 16 is
caused to fill the remaining interior of shell 18 around
barriers 24.
. Cartridge 10 is provided with foraminous opposite
sides 26 and 28 which may, as illustrated, comprise a per~
forated cover 26 and a similarly perforated bottom 28. It
is to be understood th.at the particular desi.gn of shell 18,
including parts 26 and 28 may be ~aried to meet particular
requirements without departure from the spirit of the
invention. This-invention relates more parti:cularly to the
adaptati.on of the above-described indicator 14 to respirator
cartridges in ~eneral regardless of their shapes, $izes,
types of vaporJgas sorbents and/or o-ther such design para
meters.
Top and bottom fill pads 30 and 32 of porous
material such as single or multipl.e layers of felt, gauze
and/or other fabric ar~ provided to suppor.t the ac-tivated
carbon sorbent 16, i.e. prevent loss of its particles of
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finer mesh through foraminous parts 26 and 28 oE the
respirator car-tridge.
It should be apparent that the illustrated screen-
ing at top and bottom of barrier 24 may be eliminated if
desired. In such a case, sorbent 16 would first be brought
to a level beneath barrier 24, indicator 14 is added there-
above within the confines of the sides of barrier 24 and the
cartridge finally completely filled with sorbent 16. In-
dicator 14 would thus be held in place ~y top and bottom con-
tact with the material oE sorbent 16 in the finished product.
In a preferred embodiment of the invention, in-
dicator 14 is comprised of a reagent grade sodium dichromate
and a rea~ent grade concentrated sulfuric acid suppoxted by
the carrier of granular silica gel. The silica gel ~eing of
from 3 to 3a mes~, for example, and inert, amorphous and
porous is caused to absorb the sodium dichromate-sulfuric
acid oxidizing agent, this absorpkion being purely physical.
An exemplary desira~le and highly effective for-
mulation for indicator 14 comprises, i`n approximately the
following proportions:
30 grams Na2Cr2Q7
30 ml concentrated H2SO~
- 200 ml distilled H2O
40 grams silica gel
The sodium dichromate is preferably first dissolved
in the water. The sulfuric acid is next slowly added to the
sodium dichromate-water solut~on. The resulting mixture is
then allowed to cool and, with constant stirring, the silica
gel is added. A-Eter being allowed to stand for a substantial
~ period oE time, e.g. two hours, excess solution is decanted
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~ff and the silica gel is dried, e.g, at approximatel~r225F in an air-circulating oven, for approximately 3
hours. The thus produced indicator 14 may be stored in a
gas-tight container. It is to be understood that K2Cr207
may be subs-tituted for the sodium dichromate if desired~
Actual evaluations of the foregoing sodium
dichromate indicator 14 formulation which exemplify its
ability to indicate when low concentrat.ions of organic
vapor/gas have penetrated cartridge 10 were conducted.
These involved passing through a freshly prepared cartri~ge
10. a challenge concentration of 1000 parts per million (ppm)
by volume in each evaluation of a vapor selected :Erom one :
of three common groups of organic vapors, namely; an aro-
matic c~pound (e.~g. benzene).; a chlorinated aliphatic
compound (,e.g. l,l,l-trichloroeth.ane); and an aliphatic
ketone t`e.g. butanone).. In each case, the challenge con-
centration of 1000 ppm of vapor in air was caused to pass
through the cartridge at a flow rate of appro~imately 64
liters per minute at 25 C and 5Q percent relative humidity.
~0 It was then determined when the concentration of vapor in
the ef1uent air reached 5 ppm by volume.
It i`s pointed out that this,. e~.fluent concentration
level was selected as a reference point for the reason that
the a~ore-mentioned vapors have threshold llmit values (TLV~
far in excess of 5 ppm, as do many other organic vapors of
the afore-mentioned three groups. Accordingly, this concen-
tration indicates a conservative lower limit which may be '
considered as establishing a suitable criteria for an in-
dica-tor system to respond to organic vapors. The TLV con-
centration is a level recommended by the American Conference
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of Governmental Industrial ~Iyqienists as being safe.
These evaluations were conducted both with and
without hiqh humidity equilibration. In the former in-
stances, the cartridges were preconditioned by passing 85
percent relative humidity air through them for approximately
6 hours at a flow rate of 25 liters per minute prior to
testing. In all cases, the concentration of ~apor in the
effluent cartridges were monitored by a calibrated Wilks
Miran I Single Beam IR Gas ~ectr,al Photometer and the 5 ppm
concentration level was correla-ted with a visual color change
in the oxidizing agent.
Results of the evaluations ~e,re t
COLOR OF INDICATOR 14
AT 5 ppm VAPOR
CONC~NTRATION IN
COLOR OF INDICATOR 14 E~FLUENT FROM
VAPO~ BEFORE VAPOR TEST CARTRIDGE l0
2-Butanone orange dark green or ~lack
~meth~lethylketonel
l,l,l-Trichloroethane orange dark green or black
Benzene orange dark green
2-Butanone orangea dark green or blacka
l,l,l-Trichlo~oethane orangea dark green or blacka
Benzene orangea dark greena
a=indicates results af-ter high humidity equilibration.
The oxidatlon recluction reactions for orqanic vapors
causing indicator l4 color change are, a-t least to some degree
catalyzed by light passing into and throuqh the translucent
silica gel granules.
It should be apparent from the foregoing that the
inc1icator system of the present invention is reaaily adaptable
to ~arious types and/or forms of respirator cartridges other
than that s~own herein for purposes of illustra-tion and that
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various modifications and adaptations of the precise
chemical and mechanical forms oE the invention here
shown and described may also be made to sui`t particular
requirements withou-t departure from the scope of the in-
vention. For example, -the cartridge shell 18 may be form-
ed in part or entirely of a transparent material with the
shell itself ~unctioning as window 22. Also, in connection
with matters of selecting a proper carrier for indicator
14, the carrier may comprise an opaque material such as
10porous pum;ce or a molecular sieve. In such a case, how-
ever, only the exterior coating of the oxidizing agent will
serve as the color indicator.
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