U.S. patent number 3,773,044 [Application Number 05/122,658] was granted by the patent office on 1973-11-20 for chemical breathing apparatus with alarm device.
Invention is credited to Richard A. Wallace.
United States Patent |
3,773,044 |
Wallace |
November 20, 1973 |
CHEMICAL BREATHING APPARATUS WITH ALARM DEVICE
Abstract
Chemical breathing apparatus for use by humans and adapted to
supply life-sustaining gases to the respiratory tract of a human
and having a canister carrying a chemical sorbent for treating the
gases to be utilized by the human and an electrically actuated
alarm device including means for measuring the resistance of the
chemicals for giving a warning as to how much longer the chemical
will be effective for treating gases and vapors in hazardous
atmospheres.
Inventors: |
Wallace; Richard A. (Stanford,
CA) |
Family
ID: |
22404003 |
Appl.
No.: |
05/122,658 |
Filed: |
March 10, 1971 |
Current U.S.
Class: |
128/202.22;
128/202.26; 340/657; 422/122; 96/418; 340/606; 422/117;
340/691.8 |
Current CPC
Class: |
A62B
7/08 (20130101); A62B 18/088 (20130101); A62B
9/006 (20130101) |
Current International
Class: |
A62B
18/08 (20060101); A62B 7/00 (20060101); A62B
9/00 (20060101); A62B 7/08 (20060101); A62B
18/00 (20060101); A62b 007/10 () |
Field of
Search: |
;128/142.6,203,146.2,146.6,191,188,202 ;55/274,275
;200/61.04,61.05,61.06,61.07 ;340/237,235 ;23/281 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gaudet; Richard A.
Assistant Examiner: Dunne; G. F.
Claims
I claim:
1. In a chemical breathing apparatus with an electrically actuated
alarm device for use by a human and adapted to supply
life-sustaining gases to the respiratory tract of the human who is
operating in a gaseous environment, a canister adapted to be
carried by the human, said canister containing at least one
chemical sorbent through which gases to be treated in the canister
must pass, a face piece adapted to be placed over the face of the
wearer and having communication with the respiratory tract of the
wearer, means forming a fluid flow passage between the canister and
the face piece so that treated gases which are treated by the
canister can travel to the face piece to be utilized by the wearer,
electrode means in contact with the chemical sorbent in the
canister and being in the form of spaced apart electrodes, one of
said electrodes being positioned only in the upper portion of the
chemical sorbent so that the chemical sorbent disposed generally in
the upper one-half portion of the canister presents a high
resistance between the electrodes, signalling means connected in
series with the electrodes and means for applying a potential to
the electrodes to give an indication when the resistance of the
chemical sorbent between the electrodes is substantially reduced to
thereby give an indication of the remaining effective life of the
canister.
2. A breathing apparatus as in claim 1 wherein said signalling
means includes a lamp mounted on the breathing apparatus in a
position where it can be readily viewed by the wearer of the
apparatus.
3. A breathing apparatus as in claim 1 wherein said canister is of
the filter type and is adapted to be opened to the atmosphere to
permit atmospheric air to be drawn into the canister to be treated
so that it can be utilized by the wearer.
4. A breathing apparatus as in claim 1 wherein said chemical
sorbent is provided for generating oxygen and wherein said means
establishing communication between the canister and the face piece
include means for introducing exhaled air into the canister where
it is recirculated through the canister to remove the carbon
dioxide and to introduce oxygen so that the exhaled air can be
reused by the wearer.
5. A breathing apparatus as in claim 1 together with means for
testing said alarm device to see whether or not it is
operative.
6. A breathing apparatus as in claim 1 wherein at lwats two
different chemical materials are utilized and in which chemical
sorbents are disposed in layers in the canister and wherein said
first named electrode is disposed in one of said layers.
7. A breathing apparatus as in claim 1 wherein said alarm device is
readily detachable.
8. In a chemical breathing apparatus with an electrically actuated
alarm device for use by a human and adapted to supply life
sustaining gases to the respiratory tract of the human who is
operating in a gaseous environment, a canister adapted to be
carried by the human, said canister containing at least one
chemical sorbent through which gases to be treated in the canister
must pass, a face piece adapted to be placed over the face of the
wearer and having communication with the respiratory tract of the
wearer, means forming a fluid flow passage between the canister and
the face piece so that treated gases which are treated by the
canister can travel to the face piece to be utilized by the wearer,
electrode means in contact with the chemical sorbent in the
canister and being in the form of spaced apart electrodes, one of
said electrodes being positioned only in the upper portion of the
chemical sorbent so that the chemical sorbent presents a high
resistance between the electrodes, signalling means connected in
series with the electrodes and direct current power supply means
for applying a potential to the electrodes to give an indication
when the resistance of the chemical sorbent between the electrodes
is substantially reduced to thereby give an indication of the
remaining effective life of the canister.
9. A chemical breathing apparatus as in claim 8 wherein said direct
current power supply means is in the form of a battery.
10. In a chemical breathing apparatus with an electrically actuated
alarm device for use by a human and adapted to supply
life-sustaining gases to the respiratory tract of the human who is
operating in a gaseous environment, a canister adapted to be
carried by the human, said canister containing at least one
chemical sorbent through which gases to be treated in the canister
must pass, a face piece adapted to be placed over the face of the
wearer and having communication with the respiratory tract of the
wearer, means forming a fluid flow passage between the canister and
the face piece so that treated gases which are treated by the
canister can travel to the face piece to be utilized by the wearer,
electrode means in contact with the chemical sorbent in the
canister and being in the form of spaced apart electrodes so that
the chemical sorbent presents a high resistance between the
electrodes, signalling means connected in series with the
electrodes and means for applying a potential to the electrodes to
give an indication when the resistance of the chemical sorbent
between the electrodes is substantially reduced to thereby give an
indication of the remaining effective life of the canister, said
electrode means being in the form of one electrode extending into
the chemical sorbent and the other electrode being in the form of a
body with the chemical sorbent disposed in the body.
11. A breathing apparatus as in claim 10 wherein said first named
electrode is in the form of a screen-like element disposed in the
chemical sorbent.
12. A breathing apparatus as in claim 10 wherein said first named
electrode makes electrical contact with two spaced layers.
13. A breathing apparatus as in claim 12 wherein said first named
electrode is in the form of a pair of spaced, generally parallel
screen-like members which are connected in parallel and which are
disposed in separate spaced layers.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to chemical breathing apparatus with an
electrically actuated safety alarm device and more particularly to
such chemical breathing apparatus in which the electrically
actuated alarm device measures the resistivity of at least one
chemical sorbent being utilized to ascertain when its resistivity
is greatly decreased upon the absorption of moisture or,
alternatively, irritant gases and vapors sorbed by the chemical
sorbents within the gas-filter apparatus.
2. Description of the Prior Art
Chemical breathing apparatus has heretofore been provided. There
are two types of chemical breathing apparatus: (1) the chemical
oxygen-generating apparatus known as the "Chemox"; and (2) the gas
filter apparatus for protection against harmful and irritant gases
and vapors in contaminated atmospheres.
The oxygen-generating "Chemox" breathing apparatus utilizes a dial
mechanical timer preset by the wearer. Such an indicator has been
found to be relatively unreliable because it merely gives an
indication of the passage of time and does not show the effective
condition of the chemical sorbent in the canister. In addition, it
has been found that the ringing of a bell alarm by the dial-timer
often cannot be heard over the noise in the encironment in which
the breathing apparatus is being used. It, therefore, can be seen
that such prior indicating and warning means have very undesirable
disadvantages.
Certain gas filter breathing apparatus has been provided with a
window indicator in the canister. Normally, in such a window
indicator, two pieces of paper of different colors are located
side-by-side in the window. One paper is treated chemically to
change color as it absorbs moisture. When it has changed
sufficiently in color to match the paper, this should indicate that
the chemical sorbent or chemical sorbents have lost or will shortly
lose their effectivness. In order to make a proper observation of
the colors, it is necessary that the window indicator be observed
in daylight. In addition, because of the position of the window
indicator, it is very difficult, if not impossible, for the wearer
to observe the indicator while the mask is being worn. There is,
therefore, a need for a chemical breathing apparatus with new and
improved alarm safety means.
SUMMARY OF THE INVENTION AND OBJECTS
The chemical breathing apparatus is for use by humans and is
adapted to supply life-sustaining gases to the respiratory tract of
the human from a gaseous environment in which the human is present.
The apparatus consists of a canister adapted to be carried by the
human. The canister contains at least one chemical sorbent for
sorbing and/or neutralizing gases entering the canister and which
will react with the chemical sorbent or chemical sorbents to treat
the gases so they are more suitable for use by a human. The
chemical sorbent or chemical sorbents undergo a progressive change
as additional gases pass through the chemical. A fact mask is
adapted to make connection with the respiratory tract of the
patient for supplying gases to the respiratory tract of the
patient. Means is connected to the face mask and to the canister
for supplying gases passing through the canister to the face mask.
Electrically actuated safety means is provided for giving an
indication as to approximately how much longer the chemical sorbent
will be effective in sorbing and neutralizing the gases.
In general, it is an object of the present invention to provide a
chemical breathing apparatus which has an electrically actuated
safety alarm device for giving an indication as to how much longer
the chemical sorbent will be effective in sorbing, neutralizing
and/or treating gases to be utilized by the wearer.
Another object of the invention is to provide apparatus of the
above character which gives a good indication of the remaining
service life for the canister.
Another object of the invention is to provide apparatus of the
above character which will light a lamp to give the warning or
safety alarm.
Another object of the invention is to provide apparatus of the
above character in which the lamp will remain energized for a
substantial period of time after it is first energized.
Another object of the invention is to provide apparatus of the
above character in which it is possible periodically to check or
inspect the effectiveness of the apparatus in storage.
Another object of the invention is to provide apparatus of the
above character which will tell the wearer quite accurately while
being worn the remaining time during which the apparatus will be
effective.
Another object of the invention is to provide apparatus of the
above character in which there is given an indication which is a
direct measure of the amount of remaining unused chemical sorbent
in the apparatus.
Another object of the invention is to provide apparatus of the
above character in which the alarm device is relatively inexpensive
and can be easily manufactured.
Another object of the invention is to provide apparatus of the
above character in which the alarm device is very reliable.
Another object of the invention is to provide an alarm device of
the above character which can be adapted to apparatus already in
the field.
Additional objects and features of the invention will appear from
the following description in which the preferred embodiments are
set forth in detail in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a front elevational view of a chemical oxygen-breathing
apparatus with an electrically actuated alarm device incorporating
the present invention.
FIG. 2 is a cross-sectional view taken along the line 2--2 of FIG.
1.
FIG. 3 is a circuit diagram of the electrically actuated alarm
device utilized in the embodiment shown in FIGS. 1 and 2.
FIG. 4 is a graph showing the chemical resistance of the chemical
sorbent utilized in a typical oxygen generating chemical breathing
apparatus plotted against exhalation time in minutes.
FIG. 5 is a front elevational view of a fireman wearing a chemical
gas-filter breathing apparatus with an electrically actuated alarm
device incorporating another embodiment of the invention.
FIG. 6 is a cross-sectional view taken along the line 6--6 of FIG.
5.
FIG. 7 is a circuit diagram of the electrically actuated alarm
device utilized in the embodiment shown in FIGS. 5 and 6.
FIG. 8 is an isometric view in cross-section of a canister with
another embodiment of the electrode means.
FIG. 9 is a graph showing the electrical resistance of a chemical
sorbent in a typical gas-filter breathing apparatus plotted against
exhalation time.
FIG. 10 is a graph showing the electrical resistance of a chemical
sorbent in a typical gas-filter breathing apparatus plotted against
inhalation time.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The chemical oxygen breathing apparatus with an electrically
actuated alarm device is for use by humans and is adapted to supply
life-sustaining gases to the respiratory tract of the human while
the human is operating in a gaseous environment. The apparatus
includes a canister 11 which consists of a shell 12 formed of a
suitable material such as copper-plated steel. The shell 12 can be
in the form of a deep-drawn receptacle or body 13 having a bottom
open end which is closed by a bottom wall 14 that is secured to the
body 13 by a seam 16. The receptacle or body 13 is provided with an
open neck 17 at its upper end. An open-ended tube 18 extends
downwardly into the shell 12 from the neck 18 as shown particularly
in FIG. 2. The tube 18 is formed of a suitable material such as
copper.
A suitable oxygen-evolving chemical sorbent 21 is provided within
the shell 12. This chemical 21 fills most of the space within the
shell 12 as also shown in FIG. 2. One chemical sorbent found to be
particularly satisfactory is potassium superoxide. The lower
portion of the chemical can be impregnated with a catalyst to speed
the chemical reaction to generate oxygen.
A space 22 is provided beneath the chemical and at the bottom of
the canister to permit circulation of the incoming breath through
the chemical and to ensure minimum breathing resistance. Filters 23
are provided above and below the chemical and at the top and bottom
of the canister to prevent tiny particles of the chemical from
entering the breathing system of the human while the canister is
being used. Yieldable means in the form of a spring 24 below the
lower filter 23 urges the filter 23 upwardly to provide a space 25
below the lower filter 23 so that air passing through the tube 18
will be distributed over the entire exposed surface of the lower
filter 23. When not in use, the canister is hermetically sealed to
prevent air from coming into contact with the chemical sorbent
within the canister.
The canister 11 is adapted to be inserted into a harness assembly
26. The harness assembly 26 consists of a rigid backing plate or
frame 27 that has an insulated canvas covering 28 mounted on the
same which is open at the bottom end and which is adapted to
receive the canister 11. The harness assembly also includes upper
and lower straps 29 and 31 which are adapted to encircle the body
of the human user to hold the frame 27 against the front of the
body of the user. In addition, there is provided another strap 32
which is secured to opposite sides of the frame 27 as shown and
which is adapted to pass over the shoulders and back of the neck of
the user. A U-shaped bracket 33 is pivotally mounted upon the
covering 28 and is adapted to swing below the covering 28 as shown
in FIG. 1. A screw 34 is threaded into the bracket and is provided
with a knob 36. A plate 37 is mounted on the screw 34 and is
adapted to engage the bottom of the canister.
A plunger assembly 41 is mounted upon the canister holder or
covering 28 and includes a spring-located plunger (not shown)
mounted within a hollow housing. The plunger is in the form of a
cylindrical tube with a cone-shaped tip that is adapted to pierce
an exposed copper foil provided in the neck 17 of the canister when
the canister 11 is thrust upwardly against it by the force of the
screw 34 operated by the user. The tip of the plunger is perforated
to allow the exhaled breath of the user to enter the canister. The
plunger in the form of the cylindrical tube communicates with the
tube 18 provided within the canister so that the exhaled breath of
the user will pass through the canister as hereinafter
described.
Means in the form of a face piece assembly 46 is adapted to make a
connection with the respiratory tract of the patient or user. The
face piece assembly consists of a face mask 47 formed of suitable
material such as rubber which is adapted to fit over the face of
the user and form an air-tight seal therewith. The mask is provided
with a strap assembly 48 for securing the mask to the head of the
user. The mask is provided with lens 49 to give the user visibility
through the mask. The mask is fitted with a mouthpiece assembly 51
to permit the wearer to carry on a communication while wearing the
face piece assembly 46. A manifold assembly 52 is also connected to
the face piece assembly by a pair of tubes 53 and 54. An exhalation
valve (not shown) is mounted in the left-hand side of the manifold
assembly 52 and is adapted to establish communication with an
exhalation breathing tube 56 that is connected to the plunger
assembly 41 as shown in FIG. 1. The right-hand side of the manifold
assembly 52 is provided with an inhalation valve assembly (not
shown) which is adapted to establish communication with an
inhalation breathing tube 57 that is connected to a breathing bag
58. The manifold assembly 52 is also provided with a relief valve
(not shown).
The breathing bag 58 is in the form of an inverted "U" and is
secured to the canister frame or backing plate 27. An inlet tube 59
is provided on the right-hand side or lobe of the breathing bag 58
and is in communcation with the inhalation breathing tube 57. An
outlet tube 61 is provided in the other or left-hand side or lobe
of the breathing bag and is in communication with the outer housing
of the plunger assembly 41 and with the interior of the canister 11
as shown particularly in FIG. 1. A timer 62 is carried by the
canister frame. The timer is actuated by twisting a pointer 63
clockwise as far as it will turn. This automatically sets a bell to
ring after 45 to 60 minutes as desired.
A name plate holder 65 is secured to the canister holder 28 and
carries certain instructions.
The portion of the chemical breathing apparatus thus far described
is conventional and is known under the trademark "Chemox" and is
supplied by Mine Safety Appliances Company of Pittsburgh, Pa.
Means has been provided as a part of the chemical breathing
apparatus in the form of electrically actuated alarm means for
indicating approximately how much longer the apparatus will be
effective in supplying treated life-sustaining gases to the
respiratory tract of the user. Such means consists of a pair of
electrodes 66 and 67 in which the electrode 66 is in the form of a
copper wire 68 which is covered with a layer 69 of a suitable
insulating material. The copper rod or wire 68 can be of a suitable
size such as 8 or 10 gauge. The insulation 69 for the copper wire
can be of any suitable type which will withstand high temperatures.
For example, the insulation can be formed of a polymer which will
withstand temperatures of 100.degree.C. continuously. It is
necessary that the insulation be able to withstand such a
temperature because the chemical reaction which takes place during
operation of the breathing apparatus is exothermic and generates a
large amount of heat. The electrode 66 is positioned relatively
precisely within the canister. In particular, it is positioned
sufficiently far away from the side walls of the canister so that
an appropriate resistance is developed between the two electrodes
before the canister has been used. In addition, as hereinafter
explained, the electrode 66 is positioned and has a length so it
extends to a predetermined depth within the chemical sorbent 21. It
can be readily appreciated that the greater the depth of
penetration of the chemical by the electrode, the sooner the visual
indicator will be energized. As can be seen from FIG. 2, the
electrode 66 extends downwardly into the chemical 21 for a
substantial distance and the tip of the same is free from
insulation as shown in FIG. 2 and is exposed to the chemical
sorbent.
The electrode 66 extends through an insulator 71 mounted in the top
wall of the canister and is connected to a terminal 72. The other
electrode 67 is the copper-plated canister itself. A connector 73
makes electrical contact with the copper plating on the canister
and is connected to a terminal 74 for engaging the terminals 72 and
74 and consists of snap-like connectors 76 which snap over the top
of the terminals 72 and 74 and which are carried by a flexible
carrying ring 77. Wires 78 and 79 are connected to the connector 76
and form a part of a cable 81. One end of the cable 81 is connected
to the socket 82 which carries a bayonet type lamp 83. The socket
82 with the lamp 83 are mounted in a bracket 84 which is secured to
an alligator type clip 86. The clip 86 is adapted to clip onto any
suitable part of the apparatus so that the lamp 83 can be readily
viewed by the user of the apparatus. Thus, as shown in FIGS. 1 and
2, the clip 86 can be secured to the face mask 47 adjacent one of
the lenses 49 so that when the lamp is lit, it will be readily
noticed by the user of the apparatus. The other end of the cable is
connected to snap-like connectors 87 also carried by a flexible
ring or loop 88. The connectors 87 are adapted to be secured to the
terminals 89 of a battery 91. The battery 91 is of a suitable type
which is adapted for operating with the circuitry hereinafter
described and for lighting the lamp 83. The battery 91 is removably
secured in a spring-like bracket 92 which permits the battery to be
readily inserted and removed. The bracket 92 is provided with a
hook 93 which is adapted to hook over the plate 63.
A circuit diagram of an electrical circuitry is shown in FIG. 3. As
shown therein, there is provided a resistor 96 which is in parallel
with the lamp 83 and which is also shown in FIG. 2. A pushbutton 97
in series with a resistor 98 is provided for simulating the
condition of the chemical sorbent when it becomes impregnated with
moisture, and also for the user to test the circuitry and battery
of the alarm before entering the hazardous area.
Operation and use of the chemical breathing apparatus in
conjunction with the electrically actuated alarm device may now be
briefly described as follows. The chemical breathing apparatus can
be donned by the user in a conventional manner. Thus, the straps
29, 31 and 32 can be put in place. A canister 11 can be inserted in
the canister holder 28 and punctured by the plunger assembly 41 as
hereinbefore described. Normally, the electrically actuated alarm
system is already mounted on the breathing apparatus. However, if
not, it can be readily mounted on the chemical breathing apparatus
by placing the battery 91 with its bracket 92 on the canister
holder 28. The snap connectors 87 can be connected to the terminals
of the battery and similarly the snap connectors 76 can be
connected to the electrodes 72 and 74. The lamp 83 can then be
clipped in the desired position such as mounting the same on the
mask 47 adjacent one of the eye pieces 49 or, alternatively, on the
mouth-piece assembly 51.
The user is now in a position to don the face mask 47 whenever
required as, for example, when entering a building which is on
fire. The chemical breathing apparatus in this case is a
self-generating oxygen breathing apparatus which operates
independently of ambient air. The canister contains a chemical
sorbent which upon contact with the moisture in the exhaled breath
generates oxygen to meet the breathing requirements of the user and
also absorbs exhaled carbon dioxide from the exhaled air of the
user. In use of the breathing apparatus, the air travels in the
path indicated by the arrows shown in FIG. 1. Thus, it passes
downwardly through the exhalation tube 56 into the tube 18 and down
and outwardly through the bottom of the tube into the space 25
where any increase in pressure is distributed uniformly, after
which the air passes through the chemical 21 where the carbon
dioxide is removed and the moisture in the air reacts with the
chemical to generate oxygen.
Potassium superoxide is activated by moisture in the breath,
liberates oxygen and produces potassium hydroxide which then reacts
immediately with the carbon dioxide to form potassium bicarbonate.
The gases passing through the canister thus have the carbon dioxide
removed and have oxygen added which travels upwardly through the
exterior of the housing of the plunger assembly 41, through the
tube 61, into one lobe of the bag 58, after which it is distributed
uniformly throughout the bag and enters the tube 59 and passes
through the inhalation tube 57 into the inhalation valve assembly
and then into the face piece 47, after which it enters the
respiratory tract of the user through either the mouth or the nose
of the user. The removal of carbon dioxide from the exhaled air and
the generation of oxygen by the canister provides a supply of
treated life-sustaining gases for the user from the recycled
exhaled air. It can be appreciated that moisture from the exhaled
air is absorbed by the chemical sorbent in the canister. The
moisture is first absorbed by the bottom portion of the chemical
and then the moisture travels upwardly as the bottom or lower
portion of the chemical within the canister becomes saturated.
When the chemical within the canister has been approximately 2/3 to
3/4 utilized, the moisture from the exhaled air will begin to reach
the electrode 68 which causes the chemical to serve as an
electrolyte whereby electricity will begin to flow between the
electrodek under the influence of the potential applied across the
electrodes by the battery 91. When the chemical sorbent 21 is dry,
its resistance is very high as, for example, several million ohms.
The resistance decreases as the amount of moisture in the chemical
increases. The resistance also decreases as the moisture absorption
takes place because of the increase in temperature of the chemical
sorbent caused by heat generated by the exothermic heat of
absorption reaction. A curve which is representative of the drop in
resistance in the chemical sorbent, potassium superoxide, plotted
against breathing time is shown in FIG. 4. As can be seen from FIG.
4, the resistance drops relatively rapidly with time so that after
approximately 25 minutes, a minimum resistance of slightly below
10,000 ohms is reached. At this point, the resistance is a minimum.
Slightly above this lowermost point as determined by the parallel
resistor 96, the current flow is sufficient to light the lamp 83.
Once the lamp 83 is lit, it will remain lit for a substantial
moisture period of time. It will be noted from the curve shown in
FIG. 4 that after a period of time the resistance begins to
increase gradually. It is believed that this is due, in part, to
the fact that gradually more and more of the chemical sorbent has
reacted with the moisture and also, in part to a decline in
temperature of the potassium superoxide sorbent within the hot
canister.
The user of the apparatus knows as soon as the light has come on
that he only has a limited period of time left during which the
chemical breathing apparatus will supply him with sufficient
oxygen. This, therefore, gives a warning to the user that he has
only a very limited period of time as, for example, 15 minutes
before he must leave the area. Within a very short period of time
thereafter, the chemical breathing apparatus will fail because it
will supply insufficient oxygen to support human life. In other
words, the chemical will all be used up or reacted.
This electrically actuated alarm means can be the sole warning
means or it can be supplemental to the mechanical timer alarm 62
which is provided with the chemical breathing apparatus. It can be
appreciated that in fires where there is a great deal of smoke and
a lack of light and also because of noise, a wearer of the chemical
breathing apparatus may be unable to read or hear the timer type
alarm 62. In addition, the timer 62 would not give an accurate
indication of the amount of time that is actually left in the
remaining chemical sorbent in the canister 11. The electrically
actuated alarm means gives a much more accurate indication of the
chemical sorbent remaining because the electrically actuated alarm
means will not be operated until a predetermined portion of the
chemical has been utilized as determined by the depth of the
electrode 66. The wearer of the chemical breathing apparatus will
immediately become aware when the lamp 83 is lit because it is in
front of the eye piece or lens 49. Thus, the user will receive an
alarm even though he may be in an environment in which there is
very little or no light and in which there is a great deal of
noise. In the event that the wearer is overcome in such a
situation, the lamp 83 will also indicate to rescuers the location
of the user.
By way of example, in one embodiment of the apparatus, the resistor
96 had a value of 180,000 ohms. The lamp was an NE-67 neon bulb.
The battery 91 had a suitable voltage output such as 671/2 volts.
The adjustable resistor simulates the chemical sorbent 21 in the
canister 11. It was found that when the resistance of the chemical
21 in the canister was reduced to approximately 19,000 ohms as set
by the parallel resistor 96, the lamp 83 was lit to give the
indication of the impending exhaustion of the oxygen generation. As
pointed out previously, the time required before the lamp will be
lit can be adjusted by positioning of the electrode 66. In
addition, it can be adjusted by the voltage on the battery 91 and
it also can be changed by the value of the parallel resistance 96.
As the parallel resistance is increased, the neon lamp 83 will be
fired at a lower resistance and after a greater period of time. By
way of example, when the resistance 96 had a value of 180,000 ohms,
the lamp 83 fired at 12,000 ohms and had a period of use by the
wearer of approximately 21 minutes. With this resistor, the light
remained on after the canister was completely used up. When the
resistance 96 was reduced to 120,000 ohms, the lamp fired at 8,000
ohms or after approximately 30 minutes of use by the wearer. The
light remained on for a pierod of approximately 40 minutes.
It should be appreciated that other means than that shown can be
utilized for connecting the battery to the lamp and to the
electrodes.
Thus, it can be seen that the lamp 83 serves as electrically
actuated alarm means which has many advantages over the mecbanical
timer type alarm 62 previously provided. It is relatively light and
compact and merely requires the use of a power supply in the form
of a battery and a pair of electrodes. Such alarm means is
relatively simple and gives a very positive indication of the
impending exhaustion of oxygen generation by the canister. The
alarm means can be readily removed from the apparatus if
desired.
The pushbuttom 97 is provided for testing the electrical circuitry
to be sure that it is operative before the wearer goes into a
hazardous location.
Another embodiment of the chemical breathing apparatus is shown in
FIGS. 5 and 6 and is typically called the Universal All-Service
Model Type N which utilizes a filter type canister 101. This filter
canister is generally a conventional type such as supplied by Mine
Safety Appliances of Pittsburgh, Pa.; by Wilson Products Div. of
Electric Storage Battery, Inc., Reading, Pa.; and by Acme, Inc.,
Pittsburgh, Pa. The canister 101 consists of a drawn steel
oval-shaped body 102 which has been copperplated. A bottom closure
wall 103 is provided for closing the open end of the body 102 and
is connected to the body 102 by a seam 104. A plurality of chemical
sorbents are provided within the canister 101 and are arranged in
layers in the canister 101. Thus, there is provided a large layer
106 formed of "Hopcalite" which acts as a catalyst to convert
carbon monoxide to carbon dioxide by uniting the oxygen in the air
to the carbon monoxide thus forming carbon dioxide which is a
relatively harmless gas. The Hopcalite also has considerable
absorbing powers for organic vapors and acid gases. Screens 107 and
108 are provided above and below the Hopcalite layer 106. A
suitable drying agent 109 is positioned immediately above the
Hopcalite and is formed of a suitable material such as pure
anhydrous calcium chloride and serves to prevent moisture from
reaching the Hopcalite from the top side. Another screen 111 is
provided above the drying agent 109 and a high efficiency filter
112 is provided above the screen 111. A molecular sieve 113, such
as silica gel, is positioned below the screen 108 and serves as an
absorber of ammonia and also as a drying agent to prevent moisture
from reaching the Hopcalite. A screen 114 is provided below the
molecular sieve 113. A caustite layer 116 is provided below the
screen 114 and is a soda lime which is a mixture of caustic soda
(NaOH) plus lime [Ca(OH).sub.2 ]. A screen 117 is provided below
the layer 116 and a layer 118 formed of activated charcoal is
provided for absorbing organic vapors. A screen 119 is provided
below the layer 118. An ultra high efficiency filter 120 is mounted
in the bottom of the canister and is provided for filtering toxic
dust, fumes, mist, fogs and smokes including radioactive
particulates. The bottom closure member 108 is provided with an
opening 121 which is sealed when the canister is not in use to
permit outside ambient air to enter. A spring 122 is provided in
the upper end of the canister for holding the chemical layers in
position in the canister. The canister 101 is provided with a
window indicator which warns the user when the canister is no
longer effective against carbon monoxide.
The body 102 of the canister is provided with a neck 122 which is
adapted to be connected to the lower end of a flexible breathing
tube 123 by a coupling 124. The upper end of the tube 123 is
connected to a face piece assembly 126 by a coupling 127. The face
piece assembly is provided with a mouthpiece assembly 128. It is
also provided with a lens 129 which provides panoramic vision to
the user of the apparatus. The face piece is adapted to be secured
to the head of the wearer by a strap assembly 131. A harness
assembly 132 is provided for mounting the canister 101 on the front
of the wearer and includes a strap 133 adapted to be secured about
the waist of the wearer as shown in FIG. 5 and a strap 134 adapted
to extend over the shoulders of the wearer and behind the neck of
the wearer.
The portion of the chemical breathing apparatus thus far described
in conjunction with FIGS. 5 and 6 is conventional. However, with
the present invention, electrically actuated alarm means is also
provided for giving an indication as to how much longer the
canister will be effective for treating the gases which are to be
utilized by the wearer or user. Such means takes the form of a pair
of electrodes in which one of the electrodes is in the form of a
rod 141 that is mounted in the canister and extends downwardly into
the chemical sorbents in the canister. The other electrode is the
body 102 and the bottom closure 103 of the canister which is
provided with a ground lug 142. The rod 141 is in the form of 8 or
10 gauge copper wire 143 covered by a layer 144 of high temperature
insulation of a suitable type such as a polymer. The rod 141
extends to a suitable depth within the chemicals and, as shown in
FIG. 6, the insulation from the wire 143 is removed in two
locations to expose two portions 143a and 143b of the wire 143. The
bare portion 143a is in the drying layer 109 immediately above the
Hopcalite layer and the portion 143b is disposed in the caustite
layer. The rod 141 is mounted on a terminal 146 which extends
through the top wall of the body 102 of the canister 101. A clip
147 is secured to the terminal 146 and another clip 148 is secured
to the ground lug 142. The clips 147 and 148 are connected by wires
149 and 151 to a small power supply 170. The power supply 150
consists of a housing 152 which can be clipped to the harness
assembly 132 as shown in FIG. 5. The printed circuit board 153 is
mounted within the housing and is connected to a battery 154
carried by a clip 156 within the housing. The printed circuit board
153 and the battery 154 are connected by conductors 157 and 158 to
a lamp socket 159 which is mounted upon a clip 161. A lamp 162 is
mounted within the socket 159 and is of a suitable type such as a 6
volt incandescent lamp. The clip 161 is adapted to be secured in a
location so that the lamp 162 can be readily viewed by the user of
the apparatus. Thus, as shown in FIGS. 5 and 6, the clip has been
secured to the brim of a helmet 164 so that the lamp is clearly
visible to the wearer. It also should be readily apparent that the
clip can be readily secured to other parts of the apparatus where
it would still be readily visible to the wearer.
The circuit which is utilized for energizing the lamp 162 is shown
in FIG. 7 and is mounted on the printed circuit board 153. The
circuit includes a resistor 166 that represents the variable
resistance of a chemical sorbent in the canister and a fixed
resistor 167 having a predetermined value approximately 4 - 6 times
as great as the resistance of the chemical sorbent to provide
resistance ratios ranging from 4 to 1 to 6 to 1. The junction
between the two resistors 166 and 167 is connected to the base of a
transistor Q1. The emitter of the transistor Q1 is connected to the
base of a transistor Q2. The collector of the transistor Q1 is
connected to one side of the lamp 162 and to the collector of the
transistor Q2. The emitter of the transistor Q2 is connected to one
side of the resistance 167.
There is provided a pushbutton 171 in series with a fixed resistor
172 of a suitable value such as 5000 ohms which are in parallel
with the resistance 166 representing the canister for testing the
circuit to see whether or not the circuit is operative and also to
ascertain whether or not the lamp 162 can be energized by the
circuit.
Operation and use of the chemical breathing apparatus may now be
briefly described as follows. The chemical breathing apparatus can
be donned by the wearer in a conventional manner as shown in FIG.
2. The seals (not shown) are removed from the neck of the canister
101 as well as from the opening 121 in the bottom of the canister
so that air can pass therethrough. The user can then press the
pushbutton 171 to be sure that the circuit is operative. The clip
161 is secured at a convenient location and the face piece is then
placed over the head of the user. The user is then in a position to
enter the zone in which he desires to utilize the chemical
breathing apparatus. During inhalation by the wearer of the
apparatus, air enters the opening 121 in the bottom of the canister
101 and passes into the interior. The air is thoroughly purified,
first by the filter 119, and through the various other layers of
chemical sorbents in the canister, and then through the filter at
the top, through the breathing tube 123 into the face piece, and
thence into the respiratory tract of the user. The air in passing
through the canister is thoroughly purified by the filters which
remove the large particle size dust, fumes, mists, fogs and smoke.
The layers of chemicals absorb or chemically neutralize harmful
gases and vapors.
During exhalation, the air is expelled from the face piece through
the exhalation valve 128 which, because of its location and design,
permits conversation between the wearer and others. It also serves
as a drain for moisture which may condense from the breath on the
face piece. A check valve (not shown) fitted at the top of the
canister prevents exhaled air from reentering the canister and
being rebreathed.
The Hopcalite causes the carbon monoxide to oxidize to carbon
dioxide by flameless combustion or catalysis. Thus, the canister
will gen noticably hot in the presence of carbon monoxide, in
proportion to the amount of gas passing through the canister.
Generally, filter canisters of this type are for respiratory
protection against a specific gas or group of gases which the
canister is designed in areas where there is sufficient oxygen to
sustain life (16 percent by volume) and where the total toxic gas
concentration does not exceed 2 percent volume.
Some of the chemicals utilized in such filter canisters are
particularly hygroscopic and rapidly become ineffective when they
come in contact with moisture. The electrically actuated alarm
system which iis provided as a part of the chemical breathing
apparatus is provided for sensing accumulation of moisture in the
canister. When the chemicals are dry, the resistance is very high.
The moisture begins to penetrate the chemicals from the bottom and
gradually moves upwardly in the chemicals as the chemicals on the
bottom become saturated. At the time the moisture reaches the
bottom exposed portion 143b of the electrode 141, the resistance of
the chemical will decrease very rapidly to permit operation of the
battery-operated transistor switch transistors Q1 and Q2 and to
energize lamp 162. The transistor Q1 can be of the 2N3565 NPN type.
It is a small signal silicon, high gain transistor. The transistor
Q2 can be TIP31A NPN silicon power transistor. The two transistors
Q1 and Q2 act as a voltage operated switch. Whenever the control
voltage across the resistor 167 sees the firing voltage of the
transistor switch (approximately 1.4 volts), then the transistor
switch turns on thereby allowing current to flow through the lamp
162. Thus, the decrease in chemical sorbent resistance 166 within
the canister will tend to increase the voltage developed across the
fixed resistor 167, thus turning on the lamp 162. The energization
of the lamp 162 will first be seen as a red wire glow which will
gradually be transformed to a bright light as the resistance is
decreased between the portion 143a and the canister and the circuit
is completed through the ground terminal 142. The energization of
the lamp 162 will be immediately visible to the wearer and will
warn him that he only may have a certain amount of effective time
for the filter cansiter. This will indicate to him that he must
plan to leave the area in sufficient time so that the canister will
remain effective until he is able to reach a safe area.
An exposed portion 143a is also provided on the electrode 141 and
is provided for the purpose in the event the wearer becomes sick to
his stomach and vomits, or when the wearer erroneously attaches a
different manufacturer's breathing tube to another manufacturer's
canister, or for some reason moisture comes through the neck of the
canister and starts penetrating the chemical sorbent from the top.
As soon as moisture is absorbed by the chemicals, this will be
detected by the exposed portion 143a and a circuit can be
established through the chemical sorbent serving as an electrolyte
to the side wall of the canister and to ground to activate the
transistors Q1 and Q2 to again energize the lamp 162. This again
will warn the wearer that he only has a certain amount of time
before the moisture will penetrate down to the Hopcalite and thus
warns him that the canister will only be effective for a certain
period of time so that he again must leave the area and be in a
safe place before the breathing apparatus becomes ineffective.
By positioning the electrodes in the desired location in the
chemical sorbent, it is possible to program into the electrically
actuated alarm system a predetermined amount of time after which
the breathing apparatus will no longer be effective. It is
important to note that this electrically actuated alarm system is
directly responsive to the work function which is placed on the
apparatus by the user himself and thus gives a much more accurate
indication as to how much longer the breathing apparatus will be
effective in treating the gases. This is true because the harder
the breathing apparatus is worked by the wearer, the more mosture
as well as harmful gases will be brought into the canister
filter.
In addition, the alarm device is very effective to give an accurate
warning when the breathing apparatus is being utilized in a damp or
steamy atmosphere. In such conditions, more moisture will be
brought into the canister and the breathing apparatus will be
effective for a shorter period of time. This will be indicated by
the alarm device.
The types of construction which are shown in the previous
embodiments are types in which the alarm device can be incorporated
in existing breathing apparatus. This can be readily accomplished
merely by inserting an electrode through the top wall of the
canister and by making an appropriate ground connection.
When it is desired to incorporate the alarm device as a part of the
breathing apparatus when the breathing apparatus is being
manufactured, a construction of the type shown in FIG. 8 or FIG. 6
can be utilized.
In FIG. 8 there is shown another embodiment of the electrodes for
use in electrically actuated alarm devices of the type shown in
FIG. 6 and utilized with a canister generally of the type shown in
FIG. 6. As shown therein, the terminal 146 is connected to an
insulated wire 176 which is connected at 177 to an additional
conducting screen 178 which is positioned in the middle of the
layer 109 between the screens 107 and 111 and generally parallel to
the same. Another wire 181 is connected to the wire 176 and is
connected to another additional screen 182 at 183. The screen 182
is positioned in the middle of the layer 116 parallel to the
screens 114 and 117. It can be seen that the two conducting screens
178 and 182 are disposed above and below the Hopcalite layer 106
and are connected in parallel to the terminal 146.
With this type of construction, it can be seen that the wires can
be secured to the additional screens 178 and 182 and the screens
inserted during assembly of the canister at the manufacturing
plant.
The operation of this embodiment of the invention is very similar
to that hereinbefore described. The two screens 178 and 182
connected in parallel serve as one of the electrodes, whereas the
canister itself serves as the other electrode to which the
grounding strap 142 is secured. The screens 178 and 182 are
positioned in such a manner that they are above and below the
Hopcalite and, therefore, will detect the presence of moisture in
the chemicals they are in contact with. Thus, the screens will
sense the presence of moisture coming from either direction above
or below the Hopcalite. When the resistivity of the chemicals in
which the screens 178 and/or 182 is reduced sufficiently, the lamp
162 will light to indicate to the wearer that there is only a
certain amount of effective time left in the filter canister.
With the construction shown in FIG. 8, it can be seen that very
little cost will be added to the canister in providing the
electrodes in the form of the screens 178 and 182 and the
connecting wires for the electrically actuated alarm means.
In FIGS. 9 and 10 are shown representative results which can be
obtained with an electrode system of the type shown in FIG. 8. FIG.
9 shows the curve which was obtained utilizing a Mine Safety
Appliances Model SW All-Service Filter Canister in which a copper
mesh probe having a size of 1/2 inch by 21/4 inches was inserted in
the middle of the anhydrous calcium chloride layer 109. During the
test, the check valve which prevents exhaled air from reentering
the canister was removed from the top of the canister. Continuous
heavy exhalation by the user into the canister created the curve
which is shown in FIG. 9. From the curve, it can be seen that the
resistivity remained relatively high for approximately 40 minutes
and then it dropped very sharply to approximately 10,000 ohms. This
served to indicate that the moisture penetrated to the level of the
screen which made the calcium chloride extremely conductive so that
the resistance dropped. The resistivity remained at this level for
a considerable period of time as can be seen from the curve and
thus once the light was energized, it remained on. By the
abruptness of the drop in the resistance, it can be seen that the
screen electrode is very sensitive in sensing the penetration of
moisture into the calcium chloride sorbent.
In another test of the invdntion which is shown in FIG. 10, the
same type of canister as was used in FIG. 9 was utilized. The
copper screen conductivity probe 1/2 inch by 21/4 inches in size
was inserted in the middle of the anhydrous soda lime (caustite)
layer. In this case, exhaled air was introduced through the bottom
of the canister by heavy breathing. It can be seen that the
resistance remained very high for approximately 50 minutes and then
dropped very sharply to slightly over 10,000 ohms again indicating
that as soon as the moisture reached the screen conductivity probe,
the conductivity was quite good and the circuit was operated to
energize the lamp 162. As can be seen, the resistance thereafter
remained relatively constant so that the lamp 162 remained
energized.
It should be apparent that the resistivity values are dependent
upon a number of factors, for example, the separation of the
electrodes; the length and size of the electrode mesh are also
important factors.
In any event, it can be seen that the electrically actuated alarm
device is very effective as a safety device and gives a very
accurate indication as to the remaining effective life of the
canister. Repeatable results can be readily obtained so that the
alarm device can be considered to be reliable.
The present invention is also useful in connection with gas filter
canisters for sorbing acid and basic irritable gases such as acidic
chlorine (Cl.sub.2), bromine (Br.sub.2), sulphur dioxide
(SO.sub.2), hydrogen sulphide (H.sub.2 S), hydrochloric acid (HCl),
sulphuric acid (H.sub.2 SO.sub.4), phosgene (COCl.sub.2), sulfuryl
fluoride (SO.sub.2 F.sub.2), sulfuryl chloride (SO.sub.2 Cl.sub.2),
and basic ammonia (NH.sub.3) and organic amines. It has been found
that the present invention is useful for such filter canisters
because the chemical sorbents which are utilized have their values
of electrical resistance decrease upon the absorption of moisture
and/or upon the absorption of acidic or basic gases or vapors. The
absorption of moisture is not absolutely essential since the
electrical resistance will decrease with only absorption of acid or
basic gases or vapors.
Thus, the same type of safety device as herein disclosed in
conjunction with the previous embodiments can be utilized with such
filter canisters to obtain the same mode of operation and to
thereby provide an electrically actuated alarm device which is very
effective as a safety device and gives a very accurate indication
as to the remaining effective life of the canister. Certain
representative tests utilizing canisters of this type will be set
forth below.
A Mine Safety Appliance Model GML canister, filled with chemical
sorbents consisting of layers of soda lime and activated charcoal,
was used for protection against irritable chlorine vapor. The
electrode which was inserted into this canister had exposed
portions in the two soda lime or caustite layers. Before use of the
canister, it was found that the electrical resistance of the top
soda lime layer was 15 million ohms and the lower soda lime layer
had a resistance of 6 million ohms. In testing such a canister in a
1 percent by volume of chlorine gas with a 65 percent relative
humidity at 250.degree.C., it was found that the electrical
resistance of the bottom or lower soda lime layer progressively
decreased. However, the resistance decreased quite slowly at first
and then decreased much more rapidly so that after a period of
approximately 22 minutes, the resistance was 80,000 ohms. After 33
minutes, the resistance was still further reduced to 24,000 ohms,
and at 38 minutes, the resistance was reduced to 9000 ohms. The
circuitry for the alarm device was such that the lamp was energized
to give a warning of the type hereinbefore set forth. As pointed
out above, the alarm device can be preset to any desired value of
chemical resistance which would be proportional to the amount of
advance warning required by the user.
Another canister which was tested was identified as a MIL-M-12309
canister supplied by Mine Safety Appliance under Model GMC and
consists of a mixture of activated charcoal and soda lime. The
electrode was inserted in this mixture which had an electrical
resistance of 4 million ohms. After using the canister in a
breathing chamber containing 1 percent by volume of chlorine and 65
percent relative humidity at 25.degree.C. for a period of 38
minutes, it was found that the electrical resistance began to drop
markedly and after 54 minutes, the resistance had dropped to
approximately 13,000 ohms which caused the lamp to be
energized.
Another canister was the Mine Safety Appliance Model GMD-SS used
for protection against ammonia gas and organic amines and fog.
Silica gel was used as a chemical sorbent. The initial electrical
resistance of the anhydrous silica gel was approximately 200
million ohms. On use of the canister in an atmosphere containing
21/2 percent by volume of ammonia in a relatively moist atmosphere
having a relative humidity of 90 percent at a temperature of
20.degree.C., the resistance decreased slightly for approximately
55 minutes.
As the moisture and ammonia gas progressed through the silica gel
and reached the exposed portion of the electrode in the silica gel
sorbent, the electrical resistance began to drop markedly. After
approximately 95 minutes, the electrical resistance dropped to
about 340,000 ohms which caused the warning lamp to be
energized.
Satisfactory operation of the warning device was also obtained
using it with a rocket propellant canister such as the type GMN-SSW
of Mine Safety Appliance Company. The rocket propellant canister
affords protection against nitric acid, dimethyl hydrazine,
hydrazine, and hydrogen peroxide. Each canister contains the
following layers of chemical sorbents: a top layer of activated
charcoal, a middle layer of silica gel, and a bottom layer of soda
lime. This canister is equipped with a window indicator and is
manufactured by Mine Safety Appliance Co.
The electrode rod (8 gauge) was inserted from the canister top into
the soda lime layer. The polymer insulation was removed from two
portions of the electrode rod. The lower electrode portion was
exposed to the soda lime layer over a length of three-fourths inch
from its tip. The polymer insulation was also removed from the
upper portion of this same electrode over a length of one inch and
exposed to the silica gel layer. The electrical resistance of the
soda lime layer was measured to be 100 million ohms and that of the
silica gel layer was 500 million ohms.
A small breathing chamber containing a simulated rocket propellant
atmosphere consisting of 1 percent (by volume) of nitric acid
vapor, 1/2 percent hydrazine, and 0.05 percent aniline and having a
relative humidity of 70 percent at 20.degree.C. was inhaled into
the canister, equipped with our visual warning device, preset to a
sorbent resistance warning value of 150,000 ohms. On continued
inhalations, the electrical resistance of the soda-lime layer
remained essentially unchanged for a period of about 20 minutes.
Thereafter, as the vapors progressed throughout the soda-lime
layer, the electrical resistance decreased. After 30 minutes, the
electrical resistance of the soda lime was 30 million ohms and that
of the silica gel was still high at 300 million ohms. After a
period of 50 minutes of inhalations, the resistance of the silica
gel began to drop.
At the end of 120 minutes, the canister was approaching exhaustion
in this gaseous chamber. The electrical resistance of the soda-lime
layer was about 150,000 ohms and that of the silica gel was about
110 million ohms. The visual alarm device was then activated, as
determined by preset electrical resistance values in the chemical
sorbent layer.
The above examples are representative of what results can be
obtained with canisters of this type.
It should be appreciated that in connection with the foregoing
invention that the chemical breathing apparatus can be checked
while it is in storage. In particular, the condition of the
chemical sorbents in the oxygen generating canisters and in the gas
mask filter canisters can be checked merely by measuring the value
of the electrical resistance between the electrodes. Assuming that
the electrode has been inserted during manufacture, this test can
be accomplished readily and easily so as to make sure that the
canisters are all in good condition and ready for use by firemen
and the like.
Although the present invention has been described primarily in
connection with humans, it should be appreciated that, if desired,
the same principles can be utilized for breathing apparatus for
animals such as dogs and horses.
It is apparent from the foregoing that there has been provided a
new and improved chemical breathing apparatus with an electrically
actuated alarm device which is particularly adapted for use with
various chemical type canisters for giving an indication as to when
only a certain predetermined effective time remains for use of the
canister. The alarm device will give an accurate indication even
though the breathing apparatus may be used in steamy or
water-saturated areas. The alarm device will still give an accurate
indication even though the total effective life of the canister is
greatly reduced because of the high concentration of moisture in
the air which is introduced into the canister.
The warning device can be readily observed by the wearer and will
give a true indication as to how much longer the canister will be
effective for treating the gases introduced into the canister. It
certainly is much more reliable than the color indicator which is
difficult to read and certainly difficult to observe during the
time that the canister is being worn. The alarm device is directly
responsive to the amount of air which passes through the canister.
The screens which are utilized make possible good contact with the
chemical while still permitting the air to readily pass through the
screen.
It should be appreciated that in the foregoing examples, the
canister itself was utilized as one of the electrodes. It should be
appreciated that if it is desired to not use the canister one of
the electrodes, additional electrodes can be placed within the
canister to serve this function. The alarm device can be utilized
for checking the condition of the canister before it is used.
* * * * *