US 3902485 A
An electrically actuated safety alarm system for detecting the presence of toxic gases for use alone or in combination with a conventioal gas filter breathing apparatus. Spaced electrodes, at least one of which is coated with a basic nitrogen-containing polymer of high electrical resistance project into an electrical conducting medium (e.g., activated charcoal) in a container and is connected in series with signaling means with an audio and/or visual signal. The coating forms electrically conductive quaternary ammonium salts in the presence of predetermined toxic gases to lower the electrical resistance of the polymer to complete the electrical circuit between electrodes through the charcoal and activate the signaling means to generate the signal.
Description (OCR text may contain errors)
Sept. 2, 1975 CHEMICALLY ACTIVATED WARNING SYSTEM Inventor: Richard A. Wallace, 43 Kingscote Garden, Stanford, Calif. 94305 Filed: Feb. 8, 1974 Appl. No.: 440,655
G01N 27/00; G01N 31/00 Field of Search 23/254 E, 255 E, 232 E,
23/255 R, 254 R, 254 (US. only), 252 R; 55/274; 73/23 (U.S. only), 27 R; 128/1426; 117/232; 340/237 R References Cited UNITED STATES PATENTS 4/1956 Schultze 340/237 R X 8/1965 Loscher.... 55/274 X 2/1972 Byrd 117/232 X 11/1973 Wallace 128/1426 3,831,432 8/1974 Cox 23/254 E X Primary Examiner-Joseph Scovronek Attorney, Agent, or FirmFlehr, Hohbach, Test, Albritton & Herbert [S 7] ABSTRACT An electrically actuated safety alarm system for detecting the presence of toxic gases for use alone or in combination with a conventioal gas filter breathing apparatus. Spaced electrodes, at least one of which is coated with a basic nitrogen-containing polymer of high electrical resistance project into an electrical conducting medium (e.g., activated charcoal) in a container and is connected in series with signaling means with an audio and/or visual signal. The coating forms electrically conductive quaternary ammonium salts in the presence of predetermined toxic gases to lower the electrical resistance of the polymer to complete the electrical circuit between electrodes through the charcoal and activate the signaling means to generate the signal.
14 Claims, 5 Drawing Figures ING SYSTEM BACKGROUND OF THE INVENTION This invention relates to an electrically actuated safety alarm system for detecting the presence of a threshold level of predetermined toxic gases. This alarm system includes a signal of an audio or visual type. It can be used alone as an alarm system, say, in a chemical plant or mine or used in conjunction with a conventional gas filter breathing apparatus.
Gas filter breathing apparatus typically include canisters with a layer of granular sorbent material such as activated charcoal. Such canisters generally are effective only at relatively low levels of highly toxic gas (e. g., 1 percent or less). Thus, the low capacity chin-type canisters are recommended for use at toxic gas levels below 0.5 percent. At higher levels, the material in the canister either dissipates in a relatively short period of time or sorbs only part of the toxic gas. Thus, in an emergency, particularly where a lethal spill orleak of a hazardous gas occurs, the gas mask wearer does not realize that his cartridge canister has become saturated until he detects the odor during inhalation. By that time, such inhalation may cause permanent health damage or even death. The wearer may not have sufficient time to leave the hazardous area and return to fresh air as breathing the toxic gas may cause unconsciousness.
Many of the above filter systems rapidly generate heat at high concentration of toxic gases. One warning system presently employed is that such heat causes the air inhaled by the wearer of the mask to be uncomfortably hot. However, this may be too late resulting in the above harmful effects. In addition, the wearer is likely to be so pre-occupied with performance of his emergency functions that he may not notice the heating of the canister until it is too late to leave the area. If the canister is of the type that fits on the back of the gas mask wearer, the wearer is further handicapped in noticing increased temperature of the canister, especially if he is under stress.
There are many highly toxic gases which are commonly used and which are difficult to detect for waming. Such gases include odorless and tasteless methyl bromide, used to manufacture rubber and as a fumigant in the food industries, hydrogen sulfide, occurring in natural gas and coal-mining operations, and sulfur dioxide present in coal burning and as a preservative and fumigant in the food industry.
There is believed to be no effective warning system in public use which can be positioned in various environments such as chemical plants which are rapidly activated by the sudden release of toxic gases. There is a need for such systems of an audio/visual type to warn not only those persons exposed to the toxic gases in the immediate vicinity of the alarm system but also those persons within hearing distance of the alarm system who would shortly be exposed to the gases if they do not immediately leave the premises.
SUMMARY OF THE INVENTION AND OBJECTS The electrically actuated safety alarm system of the present invention is used for detecting the presence of a selected threshold level of predetermined toxic gases (e.g., acid, acid precursor, and alkyl halide) to indicate a dangerously high concentration of such gases. The
alarm system includes a container and spaced apart electrodes with an electrically conductive medium (e.g., activated charcoal) disposed between the electrodes. At least one of the electrodes is coated with a basic nitrogen-containing polymer in the region of the electrically conductive medium to provide a barrier against contact between that electrode and the medium. The coating is characterized by high electrical resistance and is capable of reacting with a threshold level of predetermined toxic gases to form sufficient quaternary ammonium salts to substantially reduce the electrical resistance. Signaling means is connected in series with the electrodes to activate an audio and/or visual signal when the electrical resistance of the coating is reduced sufiiciently, responsive to a dangerously high concentration of toxic gases. This activation is caused by asubstantial drop in the resistance between electrodes. The container in the form of a metal canister or metal mesh basket, may serve as one of the electrodes.
The above alarm system may be used in conjunction with chemical filter breathing apparatus or independently as by mounting on a wall of a chemical plant or similar installation.
Generally, .it is an object of the present invention to provide an electrically actuated safety alarm system for detecting and signaling the presence of a selected threshold of predetermined toxic gases (e.g., acids, acid precursors and alkyl halides).
Another object of the invention is to provide an alarm system of the above type which generates an audible or visual signal or a combination of the two.
It is a further object of the invention to provide an alarm system of the above type in combination with a chemical filter breathing apparatus to provide a warning to the wearer when the apparatus is insufficient to filter predetermined levels of toxic gases.
It is another object of the invention to provide an apparatus of the above type in which the electrical signal, audio or audio/visual alarm is; readily removed for repeated use after exhaustion of the chemical systems.
It is another object of the invention to provide an apparatus of the above type in which the alarm device is highly reliable, relatively inexpensive, and can be easily manufactured.
It is a further object of the invention to provide an alarm device of the above character which can be adapted to chemical filter breathing apparatus already in the field.
It is a specific object of the invention to provide an alarm system with an audible signal which can (a) clearly warn the wearer of a chemical filter breathing apparatus of the danger of high concentrations of toxic gases even when he is pre-occupied with emergency functions and (b) signal other persons if the wearer becomes unconscious as a result of exposure to the gases.
It is another object of the invention to provide an alarm system which can be mounted for long-term usage in an area of potential danger for warning persons in the vicinity of the sudden release of toxic gases.
Additional objects and features of the invention will be apparent from the following description in which the preferred embodiments are set forth in detail in conjunction with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a front view in perspective of a man wearing a chemical filter breathing apparatus with an alarm systern according to the present invention.
FIG. 2 is an expanded front view partially broken away of a two probe electrode alarm system of the present invention.
FIG. 3 is a circuit diagram of an audio/visual assembly suitable for the present invention.
FIG. 4 is a side view partially broken away of a single probe electrode alarm system in accordance with the present invention.
FIG. 5 is a schematic view of another embodiment of a single probe electrode system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The chemical filter breathing apparatus portion of FIG. I is of a conventional chin type such as a type GMP produced by Mine Safety Appliances Company (MSA) of Pittsburg, Pa. Because of its limited capacity, this device is recommended by MSA for respiratory protection against toxic gases and vapors in concentration not in excess of 0.5 percent by volume. This breathing apparatus is illustrated in conjunction with an alarm system in accordance with the present invention. It includes an electrically conductive canister 11 consisting of a drawn steel oval-shaped body 12 which has been copper-plated. Bottom and top closure wall 13 and 14 are provided for closing the open lower and upper ends of body 12. The bottom closure wall 13 is provided with a screen opening 16 which is sealable when the canister is not in use. In a conventional breathing apparatus, a filter, not shown, is mounted in the bottom of the canister for filtering particulate material such as toxic dust and the like. A pipe 17 provides gas communication between an opening in the top wall 14 and facemask 18. The canister body 12 defines an open gas passageway through the canister so that the respiratory tract of the wearer is in communication with air from the environment after filtering through the canister.
Referring to FIG. 2, a layer 19 conventionally granular sorbent material activated charcoal, is provided within the canister 11. Activated charcoal is used to sorb a wide variety of toxic gases including organic vapors such as alkyl halides. Such activated charcoal also serves as an electrically conductive medium for purposes of the present invention.
Portions of the above conventional chemical filter breathing apparatus are utilized as an integral part of the safety alarm system of the present invention by means of the following additional apparatus. Electrode means is provided in the form of spaced apart electrode probes 22 and 23, suitably formed of copper projecting into the sorbent material 19. The electrodes are rigidly mounted to the canister side wall 12 with a portion of each electrode projecting outwardly therefrom. The probes are suitably mounted with a strong adhesive polymer, such as epoxy resin, with electrical insulating properties. The adhesive layer 20 extends a sufficient distance along the probe walls into the canister to prevent a short-circuit between the electrodes through the canister wall. Sorbent material 19 is packed in a layer to provide an electrically conductive path between electrodes 22 and 23.
Referring again to FIG. 2, a basic nitrogen atomcontaining polymer coating 24, is formed into a complete layer about electrodes 22 and 23. Initially, coating 24 serves to rovide a barrier against an electrical path between the electrodes and activated charcoal granules since it has high electrical resistance. It is further characterized by the capacity of reacting with a threshold level of predetermined toxic gases to form sufficient electrolytic quaternary ammonium salt groups in the polymer to substantially reduce the electrical resistance.
The polymer coating is deposited on the electrodes by conventional coating techniques such as by dipping the probe into a solution of the polymer in a volatile solvent, withdrawing the probe and evaporating the solvent.
Suitable basic nitrogen atom-containing polymers for coating 24 include polyvinyl pyridine, polyvinyl amine and substituted amines, amino-styrene polymer, polyvinyl piperidine, aminated polymers, and copolymers and mixtures of the above polymers together and in combination with other polymers. Copolymers with monomers which do not contain a basic nitrogen containing monomer should include a sufficient quantity of nitrogen atom-containing polymer to reduce the electrical resistance to the desired extent. Suitable monomers for copolymerization with the monomer precursors of the above polymers include vinyl compounds, dienes (e.g., butadiene, isoprene and chloroprene), styrene, acrylonitrile, vinyl acetate, methacrylic acid, and ethyl acrylate.
The different types of highly toxic gases which react with the basic nitrogen atom of coating 24 to form electrolytic quaternary ammonium salts include organic and inorganic acids, acid precursors and alkyl halides. Suitable acids include hydrogen sulfide, hydrochloric acid, nitrous acid, acetic acid, formic acid, chromic acid, chloroacetic acid, hydrogen selenide, and hydrogen cyanide. Acid precursors are defined as those gases which form acids when mixed with water and include nitrogen oxides and sulfur dioxide. Alkyl halides include ethyl or methyl chlorides and bromides.
The chemical mechanisms or quaternization of the above nitrogen compounds with toxic gases of the above type is known. The basic nitrogen atoms become converted into solid polyelectrolytes. The electrical conductivity of the electrolytes is a function of type and concentration of the toxic gases, humidity, and temperatures of the environment. Also, it is known that the presence of plasticizers such as butyl lactate and dibutyl tartrate, in nitrogen compounds such as poly-4- vinylpyridine assists this conversion to polyelectrolyte.
The initial ohmic resistance of the polymer coating on the electrode is very high (e.g., greater than l X 10 ohms). After forming of a significant number of quaternary ammonium salts by contact with threshold levels of toxic gas of the foregoing type (e.g., 1000 ppm) the resistance drops many orders of magnitude to a level of, say, 1 X 10 to l X 10 Unexpectedly, after the quaternization reaction occurs, the granular charcoal particles tend to adhere to the polymer surface, thereby forming good electrical contact between the charcoal and the converted polymer electrolyte. As set forth below, the circuit of the signaling means is complete at the lower ohmic resistance to trigger an audio/visual signal. The response time for the marked drop in resistance is dependent upon a number of factors including polymer coating thickness, percentage of nitrogen atoms in the polymer and reactivity of the toxic gas.
As described above, an electrically conductive medium is disposed in the canister between the two electrodes. The medium is preferably a form of carbon as it is effective and inexpensive. For example, activated charcoal is already present as a sorbent layer in a conventional canister for a chemical filter breathing apparatus. Thus, the two electrodes need only contact this pie-existing layer to form an inexpensive alarm device.
it has been unexpectedly discovered that the quaternization of polyvinyl pyridine by reaction with methyl bromide or chloride gas is catalyzed in the presence of granular activated charcoal. This is indicated by a comparison of the rate of drop in electrical resistance with and without charcoal.
Referring again to the drawing, signaling means generally denoted as 25 includes electrical circuitry contained in alarm housing 26. The circuitry is electrically insulated within the housing. Signaling means 25 includes an internal socket, not shown, or other suitable clamping mechanism for receiving the mounted electrode probes into the circuitry. Signaling means 25 can be detached from the electrodes when desired as after the chemical reagents in the canister are expended by use. The signaling means may generate a signal of either audible sound or visible light such as lamp 27, or both. The drop in resistance to trigger the audio/visual alarm is satisfied by conversion of the coating into an electrolytic quaternary ammonium salt in the presence of the above toxic gases so that an electrically conductive bridge is formed between electrodes 22 and 23 by direct contact with charcoal granules i9.
Suitable signaling means 25 to generate an audio and/or visual alarm in response to a dangerously high concentration of toxic gases is illustrated in FIG. 3. Lines 28 and 29 are coupled to electrode 22 and 23 as discussed previously. When the electrical insulating barrier of one electrode is still intact electrical resistance produced between lines 28 and 29 is relatively high; for example, greater than ohms. Thus, the current flow caused by the positive potential of the bat tery Bl through the series circuit of R4, R5 and the high effective resistance between lines 28 and 29 is very low. The base input of transistor Q3 is very close to the plus battery potential and is maintained in an off condition. The collector of Q3 is connected to light emitting diode Di and is also coupled to an oscillator circuit which includes transistors Qi and Q2, the resistors Rll, R2, R3, and the capacitor C1.
in operation when the nitrogen atoms of coating 241 form significantly quaternary ammonium salt groups by reaction with a dangerously high concentration of toxic gases the resistance between lines 28 and 29 is reduced. When this resistance reaches a certain point, for example 2,il0tl ohms, transistor switch Q3 is turned on which applies power to the visual alarm light emitting diode Di and at the same time activates the oscillator through resistor R3 to the base of transistor Qll. The oscillator circuit oscillates at an audio frequency which is converted to an audio signal by means of a suitable electro-mechanical transducer or loudspeaker which is tapped off between Cl and R1 as indicated on line 3%. in accordance with the invention even if the user of the device does not see the visual signal he is notified by the audible sound.
in the embodiment illustrated in FIG. 2, coatings are provided upon both electrodes. It should be understood that it is only necessary to coat one electrode as that will create the high resistance which prevents completion of the electrical circuit between the electrodes. Also, the electrically resistant coating only need be present in the area of the charcoal or other electrically conductive medium.
Referring to H6. i, another embodiment of the alarm system of the present invention is illustrated with the electrode means in different form. A canister of the same general type as described with respect to FIG. 2 is provided. Electrode 12 extends into activated charcoal layer 411 and is rigidly mounted to canister 40 with a layer of a suitable electrically insulating adhesive such as epoxy resin as set forth above. Electrode 4-2 projects through the canister for clamping into the signaling means circuit. The other electrode comprises the housing wall 43 of canister 4-0 which is formed of an electrically conductive metal. Signaling means housing $4 is titted with an electrically conductive finger 45 in electrical communication with housing wall 43. Pinger 45 is connected to the same portion of the circuit of the signaling means as one of the electrode probes 22 or 23 in FIG. 2. A coating as of the type set forth above is deposited on the surface of electrode 42.
As set forth above, the canisters may serve as the base for mounting the signaling means of the present invention by drilling a hole in the canister wall and mounting at least one electrode to project into the activated charcoal compartment. However, other electrically conductive media may be used in place of activated charcoal, such as untreated carbon granules or metal particles. These would suffer from the disadvantage that they would not perform the sorbent function described above.
The foregoing alarm system is illustrated with the electrode projecting through the side of the canister. It should be understood that such electrodes could also project through other portions of the canister housing as long as activated charcoal or other electrically conductive medium is disposed between electrodes.
The foregoing description relates to a chemical filter breathing apparatus of the chin canister type. However, it should be understood that the invention is applicable to larger canisters of both frontand back-mounted types. An audio alarm system is particularly beneficial for the chin-type or back-mounted canister because of the difficulty for the wearer of the gas mask to detect the visual warning signal.
When the alarm system is used in conjunction with a chemical filter breathing apparatus, it serves to warn the wearer of dangerously high levels of toxic gases beyond the capacity of the breathing apparatus. The exact threshold level of toxic gases which will trigger the present alarm system can be adjusted in the electrical circuitry and by the type and thickness of the polymer coating.
The above electrically actuated safety alarm system is described in terms of signaling means attached to a canister of a chemical filter breathing apparatus. The invention in its broadest aspect includes the use of the alarm system independently of the chemical filter breathing apparatus. In this case, of course, no facemask or passageway to the same is required. instead, a simple container which may be of the canister type used in the breathing apparatus may be either independently constructed or the facemask portion removed from the breathing apparatus. Also, a container of a different type from the above canister, such as described with respect to FIG. 5, may be used. Otherwise, the alarm system operates on the same principle described above.
Referring to FIG. 5, another embodiment of the invention of the general type set forth in FIG. 4, is illustrated in compact form particularly suitable for use in limited space such as a flue or gas conduit or the like. It comprises a perforate tubular cylindrical container 50 formed of an electrically conductive material such as a copper mesh screen. Electrode 51 extends into activated charcoal layer 52 and is rigidly mounted to conminer 50 with a layer 53 of a suitable electrically insulating adhesive such as epoxy resin as set forth above. Container 50 forms the other electrode. Signaling means is provided of the type set forth above and includes a housing 54. Electrical leads 56 and 57 connect and are attached to electrode 51 and container 54, respectively, to provide communication with the appropriate portion of the circuit in housing 54. A coating 58 of the type set forth above is deposited on the surface of electrode 51.
The embodiment of FIG. is well adapted to placement in a conduit of flowing gas. The signaling means is remote from the conduit as in a central control panel. Also, the open mesh of container 50 exposes the chemical component of the system to the flowing gas more rapidly than in the generally solid canister. Furthermore, the container sizing can be small enough, (e.g., 1 inch diameter by 6 inch length) to fit in a confined space.
An independent alarm system of the foregoing type may be installed in any environment of potential toxic gas presence where people might gather or be near so that it could cause a serious health hazard. It can be used to warn of a sudden massive leak or production of toxic gases to warn people to leave the area. For example, it could be employed in flue gas waste stacks, chemical plants, coal mines, pulp and paper mills, or the like. An audio alarm system is particularly effective to provide a warning in this type of environment. The alarm system could also be attached to the interior of tanker trucks which transport large amounts of toxic fluids. In the event of an unexpected leak or spill of the fluid, the driver would be alerted by the audio signal of the alarm system.
It should be understood that it may require either a longer time or a higher concentration of toxic gases to activate the independent alarm system than would be required to activate the alarm system utilized in conjunction with the chemical filter breathing apparatus. This is because in the latter case the air and toxic gases are rapidly drawn past the chemical means for generating heat during lung inflation. This is to be contrasted with the stationary independent container, say, mounted upon a wall of a chemical plant in which the toxic gases in relatively stagnant air permeate the container.
To decrease the response time of the above independent alarm system in a stagnant atmosphere, an aspirator bulb or a pump can be used to draw the surrounding air (which may contain toxic'gas) into the canister. For example, a small four-cylinder electric pump is capable of drawing a 1 percent toxic gas in air mixture into the canister at a rate of 4 liters per minute.
The alarm system of the present invention is particularly economical because it can be utilized in conjunction with a canister for a conventional gas mask as of the type manufactured by MSA. For example, in a dual electrode system, the electrodes are mounted to the canister wall to contact the signaling means. Alternatively, in a single electrode system, only one electrode probe is mounted in the canister wall since the other electrode is provided by the canister wall itself. Whether the alarm system is used alone or in conjunction with the chemical filter breathing apparatus, the signaling means may be readily mounted to a conventional canister used in such apparatus. Also, the other types of containers as described above are inexpensive to construct. Similarly, after the alarm system is triggered, the signaling means can be removed from the used canister and is reusable with fresh containers.
In order to more clearly disclose the nature of the present invention, specific examples of its practice are herein given. It should be understood, however, that this is done by way of example and is not intended to limit the scope of the appended claims.
EXAMPLE 1 The suitability of the alarm system to detect the presence of threshold levels of sulfur dioxide was tested. A conventional copper probe was used as the electrode. A coating of polyvinyl pyridine was formed on the probe by the following technique. The probe was dipped into a chloroform solution containing 10 percent by weight of polyvinyl pyridine together with 5 percent by weight of slightly crosslinked fine polyvinyl pyridine particles mesh). The purpose of using the crosslinked particles was to form a roughened textured coating. Activated charcoal of granules at a size of 8-12 mesh was deposited in an electrically conducting metal cylinder or canister to form a bed with a height of about 4 inches and a diameter of about 1 inch. The coated electrode probe was embedded into the center of the charcoal bed. The roughened texture on the probe provided good physical contact between the coating and granules.
An air stream containing 1000 ppm of anhydrous sulfur dioxide was passed through the above bed at a rate of about 4 liters of air per minute at room temperature. The following table illustrates the electrical resistance between the canister ground electrode and the copper It is apparent from the foregoing that within three to ten minutes the electrical resistance dropped many orders of magnitude as a result of the formation of quaternary ammonium salts at the nitrogen atom sites of the coating by chemical reaction with the sulfur dioxide.
EXAMPLE 2 A copper probe was coated with polyvinyl pyridine as described above. It was inserted from the top of a TABLE 2 Time (minutes) Resistance (ohms) 0.0 1.0 x 10 10.0 1.0 x 10" 11.5 3.0 10 13.0 4.0 x 10 15.0 1.5 x 10 16.0 1.0 x 10 17.0 6.0 x 10 18.0 1.0 x 19.0 4.0 x 10 20.0 3.0 x 10* EXAMPLE 3 A copper probe was coated by being dipped twice into a chloroform solution containing 10 percent by weight of polyvinyl pyridine plus 10 percent by weight of crosslinked polyvinyl pyridine particles sized at 200 mesh. Activated charcoal granules at a size of 8-12 mesh were deposited as a bed measuring five inches high in a one inch diameter copper mesh screen container. The coated probe was embedded into the center of the activated charcoal bed. The copper probe electrode and the copper cylindrical screen, serving as the other electrode, were connected to a battery-operated transistorized audio/visual alarm system of the type described herein.
Air stream containing 1.5 percent by weight of sulfur ally set forth in the drawing except that it was disposed on the top wall of the canister.
Air containing 1.5 percent sulfur dioxide at 50 percent relative humidity was directed through the canister at a breathing rate of about 25 liters per minute at room temperature. Ohmic resistance between the probe and the canister was measured as a function of time in the below table.
TABLE 4 .Run l Run 2 Time Resistance Time Resistance (minutes) (ohms) (minutes) (ohms) 0.0 1.0 X 10 0.0 1.0 X l0 20.0 1.0 X 10' 2 0.0 1.0 X 10" 22.0 4.0 X 10" 25.0 5.0 X l0 23.0 6.0 X 10 2 6.0 1.0 X 10 24.0 5.0 X l0 2 6.5 3.0 X 10 26.0 2.0 X 10 EXAMPLE 5 A copper probe was coated with polyvinyl pyridine in the manner set forth in Example 1 except that the crosslinked polyvinyl pyridine particles were present at 5 percent by weight. Each polymer coated probe was embedded in a respiratory canister type GMC-SS-l manufactured by Mine Safety Appliances.
Air at room temperature including about 1 percent by volume of anhydrous hydrogen sulfide gas was directed through the canister at a breathing rate of about 30 liters per minute. The ohmic resistance between the probe and the canister ground was recorded as a function of time of exposure.
TABLE 5 Time (minutes) Resistance (ohms) dioxide was passed at the rate of 15 liters per minute 00 1, X 1 in a one foot square duct through the bed. Ohmic resis- 22-8 8 i 8: tance of the sensor probe was measured as a function X 4 of time in the below table. 48.0 4.0 x 10 49.0 2.7 x 10* TABLE 3 55.0 2.5 1.0
Run 1 Run 2 Time Resistance Time Resistance (minutes) (ohms) (minutes) (ohms) EXAMPLE 6 00 x 0 10 X A copper probe was coated with polyvinyl pyridine X 105 in the manner set forth in Example 5. The probe was 4.0 3.0 x 10 5.0 7.0 x 10 50 50 10 X 5 60 L0 X 5 pro ected into the activated charcoal layer through the 6.0 2.0 X 10" go 2.8 X :8: side of a respiratory canister type GMC-SS-l manufac- The above alarm system was tested with the same gas at a temperature of 110C. The ohmic resistance decreased from about 1.0 X 10 ohms to about 4.0 X 10 ohms after 2 minutes exposure to the hot sulfur dioxide-laden air.
EXAMPLE 4 tured by Mine Safety Appliances. Air including 1 percent hydrogen sulfide at 50 percent relative humidity was directed through the charcoal in the canister at a breathing rate of about 30 liters per minute. Ohmic resistance as a function of time was measured in the following table.
TABLE 6 Time (minutes) Resistance (ohms) 0.0 L0 X 10" 15.0 9.0 X 10' 16.0 8.0 X 10 17.0 6.5 X 10* 19.0 5.0 X 10 21.0 1.0 X 10 EXAMPLE 7 TABLE 7 Time (minutes) Resistance (ohms) 0.0 1.0 X 10 15.0 1.0 X 10 20.0 6.0 10 22.0 1.5 10 23.0 8.0 24.0 1.0 x 10 25.0 3.3 x 10 EXAMPLE 8 A copper probe was coated with a linear copolymer of 4-vinylpyridine and styrene at a ratio of 75 percent by weight of the former to 25 percent by weight of the latter in a chloroform solution at room temperature. The poly 4-vinylpyridine-styrene coated probe was inserted into the activated charcoal layer of the canister of the type set forth in Example 6. Air including 1 percent by volume of hydrogen sulfide at 50 percent relative humidity was passed into the canister at a rate of 32 liters per minute. The probe resistance as a function of time is set forth in the following table.
TABLE 8 Time (minutes) Resistance (ohms) 0.0 1.0 x 10 16.0 1.0 x 10 17.0 8.0 x 10 20.0 3.0 x 10" 22.0 4.0 10* 24.0 1.9 10 28.0 0.9 x 10* EXAMPLE 9 TABLE 9 Time (minutes) Resistance (ohms) 0.0 1.0 X 10 18.0 1.0 X 10 23.0 2.0 X 10 24.0 2.0 X 10 25.0 v 4.0 X 10 28.0 3.0 X 10 EXAMPLE 10 A copper probe was dipped once into the coating solution containing 10 percent by weight of the poly-4- vinylpyridine, 5 percent by weight of crosslinked polyvinyl pyridine, and 5 percent by weight of a high molecular weight polyester benzoate plasticizer in chloroform at room temperature. The plasticized coated probe was inserted through the top of a respiratory canister type GMA manufactured by Mine Safety Appliances containing activated charcoal only. Air including 500 ppm of methyl bromide at percent relative humidity was passed through the canister at a breathing rate of about 20 liters per minute. Probe resistance as a function of time is set forth in the following table.
TABLE 10 Time (minutes) Resistance (ohms) 0.0 10 10 15.0 10 x 10 16.0 3 0 x 10 18.0 1.0 x 10 25.0 10 10 30.0 7 5 10 EXAMPLE 11 TABLE I 1 Time (minutes) Resistance (ohms) 0.0 1.0 x 10 10.0 1.0 X 10 14.0 1.0 x 10 19.0 1.5 x 10 25.0 1.0 x 10 28.0 4.0 x 10 EXAMPLE 12 Apparatus using the canister of Example 1 l was utilized. In this case, not only was the copper probe coated with the polymer but also a copper screen separator which divides sorbent layers of activated charcoal within the canister was coated with the same polymer. The screen measured 6% inches in length by 3% inches in width. The periphery of the polymer-coated screen was covered with an electrical insulator, cotton, to prevent short-circuiting with the metal canister. The results of passing the same gas through the system were similar to the foregoing ones except that the resistance was slightly higher throughout the run.
EXAMPLE 13 A copper probe was dipped into a solution containing 10 percent linear poly (4-vinylpyridine) in chloroform in the absence of plasticizer. The coated probe was inserted through the top of an activated charcoal container respiratory container, type GMA manufactured by Mine Safety Appliances Co. The wall of the canister served as the ground electrode. Air including 2 percent methyl chloride was directed through the canister at a breathing rate of about 25 liters per minute. The canister was tapped gently to insure good electrical contact between the charcoal granules and the polymer coating. Ohmic resistance as a function of time is set forth in the following table.
T ABLE 12 Time (minutes) Resistance (ohms) 0.0 1.0 10 15.0 1.0 x 21.0 4.0 x 10 26.0 3.0 x 10 30.0 1.0 x 10 EXAMPLE 14 TABLE 13 Time (days) Resistance (ohms) O 1.0 X 10" l 9.0 X 10 2 2.0 X 10 4 5.0 X 10 The above experiment illustrates that probe resistance declines with canister shelf-life or residence time of methyl bromide absorbed on activated charcoal. The methyl bromide tends to desorb and migrate through the activated charcoal layer within the canister.
EXAMPLE A polyvinyl pyridine-coated probe was inserted into an activated charcoal layer as set forth under Example 1. In successive experiments, the probe was exposed to high concentrations of sulfur dioxide, methyl bromide, ethyl bromide, and hydrogen sulfide in humidified air at about 50 percent relative humidity at room temperature. In each case, within about 6 minutes of exposure time, the resistance dropped many orders of magnitude, from 10 ohms to about 10 ohms.
When the above experiments were repeated with the same vapors heated to 80C, the resistance dropped more rapidly. It is believed this is due to an acceleration of the quaternization reaction at higher temperatures.
The above experimental result held true at the same high concentration with the following substitutes for polyvinyl pyridine for polymer coatings: polyvinyl amines; copolymers of 4-vinyl pyridine and styrene; poly (para-aminostyrene); and poly (4-vinyl piperidine).
EXAMPLE 16 A number of different runs using an electrode probe system of the type set forth generally in Example 1 with polymer coatings including polyvinyl pyridine, poly (4- amino styrene) and polyvinyl amine perform with exposure to 0.5-2.0 percent by volume of the following acidic gaseous contaminants in air at 50 percent relative humidity: formic acid, chromic acid spray, acetic acid, chloroacetic acid, nitrous acid, nitric acid, hydrogen selenide, hydrogen cyanide, hydrogen fluoride, and hydrochloric acid.
in each case electrical resistance had dropped by at least 2 to 3 orders of magnitude (e.g., at least to 1000 times) after several minutes of exposure to room temperature. This illustrates a rapid quaternization reaction rendering the above coatings suitable for use in the above alarm system in the presence of the above acid gases.
l. in an electrically actuated safety alarm system for detecting and signaling the presence of a selected threshold level of predetermined toxic gases, a container; electrode means in the: form of spaced apart electrodes; and electrically conductive medium dis posed in said container between said spaced apart electrodes; a coating on at least one of the electrodes disposed in the region of said electrically conductive medium and comprising a basic nitrogen atom-containing polymer of high electrical resistance capable of reacting with a threshold level of predetermined toxic gases selected from the group consisting of acids and Lewis acids to form sufficient electrolytic quaternary ammonium salt groups in the polymer to substantially reduce said electrical resistance, and signaling means connected in series with the electrodes and including means for generating a signal responsive to the reduced electrical resistance.
2. An alarm system as in claim l in which said polymer is selected from the group consisting of polyvinyl pyridine, polyvinyl amine and substituted amines, aminostyrene polymer, polyvinyl piperidine, and copolymers and mixtures of the same.
3. An alarm system as in claim 1 in which said signaling means includes audible sound generating means.
41. An alarm system as in claim 1 in which said signaling means includes a lamp.
5. An alarm system as in claim 1 in which said electrically conductive medium comprises a layer of granular material in the container.
6. An alarm system as in claim 5 in which said medium comprises activated charcoal granules.
7.. An alarm system as in claim 1 in which said electrode means comprises an electrode probe extending into the electrically conductive layer and body with the electrically conductive layer disposed in the body.
d. An alarm system as in claim 1 in which said electrode means is in the form of one electrode extending into the electrically conductive layer and the other electrode is a screen.
9. An alarm system as in claim l in which said electrodes comprise two spaced apart probes extending into the electrically conductive layer.
lib. An alarm system as in claim l in which said signaling means is detachable from said container.
1 l. in a chemical filter breathing apparatus with electrically actuated safety alarm system for detecting and signaling the presence of a selected threshold level of predetermined toxic gases, a facemask; a container with a gas passageway between the surroundings and the facemask, electrode means in the form of spaced apart electrodes; electrically conductive medium disposed in said container between said spaced apart electrodes; a coating on at least one of the electrodes disposed in the region of said electrically conductive medium and comprising a basic nitrogen atom-containing polymer of high electrical resistance capable of reacting with a threshold level of toxic gas selected from the group consisting of acids and Lewis acids to form sufficient electrolytic quaternary ammonium salt groups to substantially reduce said electrical resistance; signaling means connected in series with the electrodes and inprises a layer of activated charcoal granules.