Abstract:
The present disclosure relates to methods and apparatus for detecting when respiratory cartridges of a respirator have reached their end-of-service-life. In some instances, two or more respiratory cartridges are removably connectable to a respirator housing, where each of the two or more respiratory cartridges receives ambient air and deliver cleaned air to the respirator housing. One of the respiratory cartridges may be configured to have a lower adsorption capacity than the remaining respirator cartridges. A gas sensor may be situated downstream of the reduced capacity respirator cartridge, and may detect an increased concentration of the targeted gas in the cleaned air delivered by the reduced capacity respiratory cartridge. When detected, an end-of-service-life indication may be provided to the user.

Description:
BACKGROUND 
       [0001]    The present disclosure relates generally to air purifying respirators having one or more replaceable respiratory cartridges, and more particularly, to methods and apparatus for detecting when the respiratory cartridges have reached their end-of-service-life. 
       SUMMARY 
       [0002]    The present disclosure relates generally to air purifying respirators having one or more replaceable respiratory cartridges, and more particularly, to methods and apparatus for detecting when the respiratory cartridges have reached their end-of-service-life. In one illustrative instance, a respirator may include a respirator housing for providing cleaned air to a user. Two or more respiratory cartridges are removably connectable to the respirator housing, where each of the two or more respiratory cartridges receives ambient air and deliver cleaned air to the respirator housing. 
         [0003]    One of the respiratory cartridges may be configured to have a lower adsorption capacity than the remaining respirator cartridges. A gas sensor may be situated downstream of the reduced capacity respirator cartridge, and may detect an increased concentration of the targeted gas in the cleaned air delivered by the reduced capacity respiratory cartridge. This may provide an early warning of when the remaining respirator cartridges are about to reach their end of life. A controller may issue an end-of-service-life indication to the user, indicating that all respirator cartridges should be changed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0004]      FIG. 1  is a diagram of a tube which may be added inside a PAPR respirator housing fitted to an outflow of a cartridge; 
           [0005]      FIG. 2  is a diagram of an overall view of a system incorporating an arrangement of  FIG. 1 ; 
           [0006]      FIG. 3  is a diagram of a graph showing harmful gas concentration at a user over time; 
           [0007]      FIG. 4  is a diagram of a graph illustrating a cartridge breakthrough; 
           [0008]      FIG. 5  is a diagram of an optional cartridge and its flow pattern; 
           [0009]      FIG. 6  is a diagram similar to  FIG. 2  except that another cartridge is added with its input connected to an output of a valve via a conveyance; 
           [0010]      FIG. 7  is a diagram similar to that of  FIG. 6  except in this illustrative example the optional cartridge is downstream from all of the other cartridges rather than just one of them; 
           [0011]      FIG. 8  is a diagram of an alternative to the optional cartridge in  FIG. 5 ; and 
           [0012]      FIG. 9  is a diagram of a table showing illustrative maximum values for a flow ratio of cartridges in dependence of times and cartridge capacities in one illustrative arrangement. 
       
    
    
     DESCRIPTION 
       [0013]    Many modern respirators appear to have no indicator when a breakthrough of harmful gases occurs in their cartridges, which would represent the end-of-service-life of the cartridges. In the past, a few cartridges have had a coarse colorimetric indicator to indicate a breakthrough of some special gases, but many of these cartridges are no longer on the market. In many cases, the user simply has to rely on making conservative estimates from data in tabular form as to when their cartridges will reached their end-of-service-life, which often leads to disposing of cartridges that have much remaining life. This often premature changing of cartridges increases the overall costs of using cartridges, and can reduce productivity. 
         [0014]    For the next generation PAPR (powered, air purifying respirators), an end-of-service-life indicator (ESLI) may be used to detect breakthrough of harmful gas and then warn the user. For increased market penetration, the end-of-service-life indicator (ESLI) should: have a relatively low cartridge cost, particularly since the cartridges must be routinely replaced during use of the powered air purifying respirator; and produce a reliable and accurate warning before 90 percent of the useful life of the cartridge is gone, which is a regulatory requirement from the National Institute for Occupational Safety and Health (NIOSH). In many cases, the harmful gas should not exceed the exposure limits at the user during the useful life of the cartridge. 
         [0015]    One way of adding an ESLI to a respirator is to mount a gas sensor inside one or more of the cartridges, sometimes with an absorbent downstream of the gas sensor. The gas sensor could then be used to give a warning upon detection of the targeted harmful gas. This approach, however, may significantly increase cartridge costs, and may complicate communication with the sensor. Additionally, one would likely need to have a power supply such as either a disposable battery in the cartridge (costly) or additional wiring in the thread from the respirator housing. 
         [0016]    Another way of adding an ESLI is to mount a gas sensor within the respirator housing itself. For example, in a PAPR, one may mount an ESLI sensor in a respirator housing, where the sensor can be used multiple times (i.e. for multiple cartridges) and may tap into power that is supplied for the pump and/or other components. When such power is readily available, there are many robust commercial gas sensors available with known reliability characteristics and sensitivities. With the sensor position in the respirator housing, as opposed to the cartridges, the sensor may more easily communicate with a local microprocessor or microcontroller, if desired. The size limit for sensors in this configuration may also be larger than for sensors in a cartridge, as is the power limit, compared to battery driven sensors. If size and power have larger limits, there may be more sensors available that can measure concentrations of a volatile organic compound (VOC) and/or other gases in the lower ppm range. 
         [0017]    To protect the user from exposure to harmful gas concentration, one may modify one or more of the cartridges using the following configuration. From the multiple cartridges used in a typical PAPR, one cartridge may be configured to have a lower adsorption capacity for the targeted gas(es). This may help ensure that this cartridge will be the first to breakthrough. One may place a gas sensor at the outflow of this cartridge, and sometimes inside the PAPR respirator housing. When the sensor detects a gas breakthrough, an optional valve may be provided to stop any additional flow through the selected cartridge. The flow through the remaining cartridges may thus be increased, to keep the total flow relatively constant for the user. At the same time, the system may warn the user and ask the user to replace all cartridges with new ones at this time. In some cases, at the time of sensor alarm, the user may be exposed to some elevated concentrations of the targeted gas(es) for a short time, but the concentrations would preferably remain below the short term exposure limit. 
         [0018]    A PAPR may have enough power (currently 4-5 watts) to provide a small amount of power to the gas sensor(s). It can be estimated that an addition of the selected gas sensors and optional valve may increase the cost of the PAPR system by, for example, 20-40 percent. The cost of a cartridge set may remain relatively low because the gas sensor(s) need not be replaced when the cartridge set is replaced. The maintenance intervals for the sensor could coincide with the maintenance of the PAPR housing and its pump. 
         [0019]    In one instance, and as described above, one cartridge may be made deliberately smaller or otherwise made to have a lower adsorption capacity for the targeted gas(es) than the other cartridge(s) of the PAPR. An ESLI sensor and an optional valve may be placed downstream of the smaller cartridge. In other instances, one of the cartridges may be effectively split into two separate cartridges, with one of the split cartridges positioned downstream of the other, and with an ESLI sensor positioned between the two split cartridges. 
         [0020]    In the presence of a PAPR herein, one may note several items. One is that the users may mount multiple new cartridges of one cartridge set, but one of the cartridges, cartridges B (cartridge  18  in  FIG. 2 ), would not be interchangeable with the other cartridges. In one example, the thread  36  of cartridge  18  may have a widely different thread size, to help prevent mounting the cartridges in the wrong place on the PAPR housing. Only the other cartridges, A 1  (cartridge  21  in  FIG. 2 ), A 2  (cartridge  22  in  FIG. 2 ), and so forth, would be interchangeable. 
         [0021]    In some cases, one may mount a tube inside the respirator housing, fitted on the outflow of the cartridge  18  that has a reduced absorption capacity. The tube may be equipped with a gas sensor for the targeted gas, and may also include a two-way valve of which both can be connected to the PAPR&#39;s microcontroller. 
         [0022]    The respirator housing may have a microcontroller to read the sensor signal, control the pump, control the valve, send warnings to the user, calculating noise cancellation, communicating with a base station, and/or perform other control and/or communication functions, as desired. 
         [0023]    In one or more illustrative examples, as described herein, or in other respirator configurations, features and/or structure of a respirator housing may be integrated into a corresponding mask. In such cases, the terms “respirator housing” and “mask” may be used interchangeably to refer to same item in some of the examples disclosed herein, and other configurations. Also in some examples and other configurations, certain features and/or structure of the pump and its respective housing may similarly be integrated, in part or in whole, into the mask. 
         [0024]    Turning now specifically to the Figures, where  FIG. 1  shows a tube  11  which may be added inside a PAPR respirator housing fitted to an outflow of a cartridge  18  of  FIG. 2 .  FIG. 2  is a diagram of an illustrative PAPR system. In  FIG. 1 , tube  11  is shown having a two-way valve  12  with an electrical connection  13  and  14  for actuation. There may also be a gas sensor  15  probing the interior of tube  11 , with electrical connections  16  and  17 . The gas sensor  15  may be used for detecting a breakthrough of cartridge  18 , which as indicated above, may have a reduced absorption capacity than cartridges A 1   21  and A 2   22 . Tube  11  may be added to a respirator housing  23 , if desired. 
         [0025]    A breakthrough from an input flow  33  of harmful gases to an output at thread  36  should occur first at cartridge  18 . The gas sensor  15  positioned downstream of cartridge  18  may detect the breakthrough and provide a warning to the user to exchange the whole set of cartridges  18 ,  21  and  22 . At the same time, the valve  12  may stop further flow through cartridge  18 , and the pump  19  may increase the flow through cartridge  21 , cartridge  22 , and so on, to maintain a relatively constant flow to the user. 
         [0026]    A question may be how much unfilled absorbent is left in the cartridges  21 ,  22 , and the like, when the breakthrough of cartridge  18  occurs. Multiple cartridges in parallel are not necessarily filled at exactly the same rate, but the deviations between them may be normally small, typically less than 3 percent. Therefore, monitoring only one of the multiple cartridges  18 ,  21  and  22 , is believed to be sufficient to give a warning to the user that it is timely for all cartridges to be changed. 
         [0027]    Rather than placing the gas sensor  15  upstream of the valve  12 , it is contemplated that the gas sensor  15  may be placed downstream from valve  12 , as long as its ambient is predominantly gas from cartridge  18  when the gas flows through cartridge  18 . After valve  12  is closed, the gas sensor downstream of the valve  12  could sense gas from the cartridges  21 ,  22 , and so on. If one of those cartridges has a breakthrough, such a gas sensor  15  downstream of the valve  12  could give a warning to the user to immediately leave the area of harmful gas. 
         [0028]    One may need to choose right materials for the added tube and components, to avoid gas absorption inside respirator housing  23 , otherwise the materials could outgas after the cartridge set is replaced, which could trigger an alarm or do other unwanted things. 
         [0029]    One may also make all threads for cartridges  18 ,  21 ,  22  the same and allow the cartridge  18  to be mounted on any of the three or more threads. However, one may need to equip every outflow with a tube  11  having a sensor  15  and a valve  12 , which may increase costs. 
         [0030]    In the PAPR system of  FIG. 2 , and around the time of the warning, the user may be exposed to some elevated gas concentrations for a short period of time, but the concentrations would likely remain below the short term exposure limit. 
         [0031]    There may be an air flow input  31  for cartridge  21 , an air flow input  32  for cartridge  22 , and an air flow input  33  for cartridge  18 . There may be a thread  34  for cartridge  21 , a thread  35  for cartridge  22  and a thread  36  for cartridge  18 . While threads are mentioned here for connecting the cartridges to the respirator housing  23 , it is contemplated that any suitable connector may be used, such as a bayonet style connection, a clamp type connection, or any other suitable connection as desired. 
         [0032]    During use, air may be pumped out through an exit tube  37  by pump  19 . In some cases, there may be a microphone  38  for noise monitoring in exit tube  37 . Also, inside exit tube  37  may be a loudspeaker  39 , which may provide an audible alarm with detailed warnings, and in some cases, for noise cancellation. 
         [0033]      FIG. 3  is a graph showing harmful gas concentration at the user over time for the system shown in  FIG. 2 . The graph has a curve  43  starting at time  41  and running for a period T 1  of time to time  25  where a peak  24  is noted. From time  25  to time  26  is a period T 2  of time. At time  26 , the gas concentration is shown to suddenly increase. The National Institute for Occupational Safety and Health (NIOSH) appears to have a requirement that T 2 &gt;(T 1 /9). Level  42  may be a threshold of harmful gas concentration; in other words, level  42  may be regarded as a short term exposure limit. Time  25  is when a breakthrough may be detected in cartridge  18 . Time  26  is when a cartridge  21  or cartridge  22  breakthrough may be detected. During time T 2 , the user may exit the contaminated environment and change the cartridge set without haste. 
         [0034]    Gas concentration at a user over time may be described as follows. First, a gas may stream through all cartridges, with the flows “a” (i.e., total flow through cartridges  21 ,  22 , and so on) and “b” (i.e., flow through cartridge  18 ), where the total flow=a+b. 
         [0035]    Second, after a time  25 , T 1 , cartridge  18  may be filled, and the target gas may breakthrough cartridge  18 . The sensor  15  may give a warning to exchange the cartridge set. In some cases, a relatively small concentration of target gas may reach the user at this point (i.e., peak  24 ). Third, valve  12  may be closed and only cartridges  21 ,  22 , and so on, continue to provide purified air for the user. Their added flow rates may be increased, from “a” to “a+b”, to maintain a relatively constant total flow. Cartridges  21 ,  22 , and so on, may now be filling slightly faster with target gas than when gas also flowed through cartridge  18 . 
         [0036]    Fourth, after another time  26 , T 2 , the cartridges  21 ,  22 , and so on, may become filled, and the target gas would have reached the user with an ambient concentration if the cartridges had not yet been exchanged by the user. 
         [0037]    The height of the indicated peak  24 , P, should be below the acceptable short-term exposure limit. With reference to  FIG. 4 , the peak height may depend on the following various parameters: a) alarm threshold of the sensor  15 , S (not too low so as not to be triggered by noise); b) response time  27  of sensor  15 , T; c) increase of gas concentration at the sensor  15  after breakthrough, R, which shows slope  28  of gas increase after cartridge  18  breakthrough; and d) the ratio of the flows (b/a) cartridge  18  flow/cartridges  21  and  22  flow. 
         [0038]    Relative to  FIG. 4 , the black curve  44  may start at time  41 . Level  45  shows S=alarm threshold. A cartridge  18  breakthrough may occur at time  46 . The breakthrough of cartridge  18  may be detected at time  47 . The time difference  27  between occurrence and detection may be regarded as T=sensor response time. From time  46  to  47 , an R=slope  28  of gas increase after the breakthrough. At the top of the slope on curve  44  at time  47 , S+R*T may be noted. The top  48  of curve  44 , where the concentration of gas at the sensor  15  stops increasing, may be indicative that the valve is closed and the flow through cartridge  18  stops. 
         [0039]    The black curve  44  shows the expected sensor signal over time, and the grey envelope  29  indicates the uncertainty of the sensor signal. The following items may be noted. 
         [0000]      Peak height  P =( S+R*T )* b/ ( a+b )=about=( S+R*T )*( b/a ) if ( b/a )&lt;&lt;1. 
         [0040]    R may depend on the absorbent, and the kind of gas and its ambient concentration (the present ESLI approach may have little influence on those). 
         [0041]    S and T may depend on the sensor type; both should be small in this configuration. 
         [0042]    (b/a) may depend on the choice of dimensions of the system. A low (b/a) may bring down the peak height. 
         [0043]    One should choose S, T, and (b/a) carefully and use a limit for R. One suitable upper limit for R may be the measured R value for the considered cartridge type using the concentration of the harmful gas that is immediately dangerous to life, above which the air purifying respirator cannot be used. 
         [0044]    On the other hand, the ratio (b/a) should not be designed too small. Otherwise the cartridge  18  may lose its function as being the cartridge with the first breakthrough. The lower bound of (b/a) (or upper bound for (a/b)) may depend on the ratio of the capacity of the cartridges and on the required safety margin. For example, for a constant concentration of the harmful gas in the ambient, a ratio of capacities of 5 and a desired time before breakthrough of 33 percent, one may find that (a/b) should be below 3.02 or (b/a) should be above 0.33. 
         [0045]      FIG. 5  is a diagram of an optional (e.g. fourth) cartridge B 2  (i.e., cartridge  51 ) with a thread  52 . A flow may enter at entry  53 , and do a U-turn at location  54  and exit cartridge  51  at exit  55 . If the peak of gas exposure around the time of the warning is unacceptable, the fourth cartridge  51  may be placed downstream of the gas sensor  15 , and would absorb any harmful gas that breaks through cartridge  18 . 
         [0046]    It may be desirable that all cartridges be mounted in the same way on the pump house  23 , to make the exchange easier for the user. Cartridges  21 ,  22 , and so on, and cartridge  18  may receive their incoming air from the ambient environment and may look similar to today&#39;s cartridges. Cartridge  51 , however, may receive its incoming air from the respirator housing  23  and give its outgoing air back into the respirator housing  23 . A cartridge  51  construction may let the gas make a U-turn in the cartridge and still separate the incoming and outgoing gas streams reliably from each other, as shown on  FIG. 5 . 
         [0047]    In some instances, both cartridges  18  and  51  would be screwed into their specific positions and have specific thread sizes so as not to permit them to be interchangeable with the other cartridges  21 ,  22 , and so on. 
         [0048]    If the cartridge  51  is large enough, the valve  12  may not be needed and may be optional. If valve  12  is eliminated, harmful gas from cartridge  18  would be absorbed in cartridge  51 , between the times of the warning and the exchange of all of the cartridges with replacement cartridges. 
         [0049]      FIG. 6  appears similar to  FIG. 2  except that the fourth cartridge  51  is shown with its input  53  connected to an output of valve  12  via a conveyance  50 . The output  55  of cartridge  51  may have a flow into housing  23 . 
         [0050]    An option of the present approach may incorporate a PAPR with three cartridges  18 ,  21  and  22 , a valve  12 , and a simple cap to cover the thread port for the fourth cartridge  51 . Another option may be to exchange the cap with the fourth cartridge  51  to eliminate the gas peak, when desired. 
         [0051]      FIG. 7  is a diagram similar to that of  FIG. 6  except in this illustrative example the optional cartridge  51  may be downstream from cartridges  21 ,  22  and  18  rather than just from cartridge  18 . Outputs from these cartridges may go to an input  62  of the U-turn cartridge  51 , go through cartridge  51  and then to an output connected to a conveyance  60  that goes to pump  19  for exhaust though exit tube  37 . 
         [0052]    Another way to have the function of the fourth cartridge would be to add an adapter to cartridge  18  that contains a location for a sensor  15  and a downstream absorbent of cartridge  51 .  FIG. 8  is a diagram of one such adapter. In  FIG. 8 , there is shown a smaller cartridge  55  (similar to cartridge  18  discussed above), which may hook into a threaded holder  56 . A sensor  57  and a buffer cartridge  58 , in that order, may fit into the holder  56 , and the holder  56  may be connected to the housing  23 . 
         [0053]    In some instances, there may be an audio alarm for the PAPR provided inside the tube to the mask or hood for several reasons. If PAPR is carried on the back where a wearer could not see an LED reliably, acoustic (and/or vibrational) signals could still be sensed by the user. The acoustic signal may also be used to ask the user to look onto a display. An audio signal inside the tube  37  may be less weakened on its way to the user&#39;s ear and, therefore, be more reliably received in a noisy environment. It is contemplated that multiple alarm types may be incorporated, e.g., audio, visual, vibrational, and so forth. 
         [0054]    Another goal may be to help reduce the pump noise to the user. Examples may incorporate using a muffler between pump  19  and the user, using an absorbent between the pump and user as the muffler and as an absorbent to prevent gas coming to the user especially after the smaller cartridge  18  has a breakthrough, and/or measuring the pump noise with a nearby microphone and canceling the noise with the loudspeaker. In some cases, sound from the loudspeaker may be provided in opposite phase to the pump noise so as to cancel out most of the pump noise before reaching the hood or mask. If a loudspeaker is needed anyway for warnings by the ESLI system, then a loudspeaker inside the tube may also be used for active noise cancellation. To help control these and other functions of the PAPR, a microcontroller  69  may be placed in or connected to respirator housing  23 . 
         [0055]    Another approach may be to implement an end-of-service-life indicator for the dust filters. A comparison of pump power and measured pressure drop over the cartridges or measured flow in the tube may give a measure of the clogging of the dust filter. However, the comparison of pump power and sensor data may require extra circuitry, such as that of microcontroller  69 . The microcontroller may be used for many purposes, like canceling noise, generating appropriate audio alarms, and controlling the ESLI. 
         [0056]    A needed minimum ratio of flow (b/a) may be calculated herein. Various parameters may be indicated with designations as in the following. 
         [0057]    Capacity of cartridges  21 ,  22 , and so on=Am 
         [0058]    Flow through cartridges  21 ,  22 , and so on=a 
         [0059]    Capacity of cartridge  18 =Bm 
         [0060]    Flow through cartridge  18 =b 
         [0061]    T 1 : time from start until flow through cartridge  18  is stopped 
         [0062]    T 2 : time from stopping flow through cartridge  18  to breakthrough of cartridges  21 ,  22 , and so on 
         [0063]    For same absorbent and gas, one may assume: 
         [0000]      Time*Flow —   X= Load —   X (time) 
         [0064]    When Load (time) reaches Capacity, then the cartridge in question is filled enough to no longer protect the user sufficiently 
         [0000]      ( T 1−response time)* b=Bm= about= T 1 *b  
 
         [0000]      and 
         [0000]        T 1 *a= Load —   A ( T 1) 
         [0000]        T 2*( a+b )+Load A ( T 1)= Am=T 2*( a+b )+T1 *a    
         [0065]    A designer might choose different percentages, p, of T 2  on the total time T 1 +T 2 : 
         [0000]        T 2= p *( T 1 +T 2)=&gt; T 2 =T 1* p /(1− p )
 
         [0000]        Am=T 2*( a+b )+ T 1 *a=T 1*( a*p )/(1 −p )+ b*p/ (1 −p )+ a )= T 1*( a/ (1 −p )+ b*p/ (1 −p )) 
         [0000]        Bm=T 1 *b=&gt; ( Am/Bm )=( a/b )/(1 −p )+ p/ (1 −p )=&gt;( a/b )=(1 −p )*( Am/Bm )− p  
 
         [0066]    (b/a) may have a lower limit above which the cartridge  18  cannot function as a warning cartridge anymore where each breakthrough occurs. (a/b) consequently may have an upper limit, which should not be exceeded. 
         [0067]    A table  61  of illustrative maximum values for (a/b) in dependence of p and of (Am/Bm) is shown in  FIG. 9 . A six-sigma process may be used to assure NIOSH compliance when determining the values in the table, by relating the gas absorption capacities and the flow resistances of the various cartridges to each other. 
         [0068]    In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense. 
         [0069]    Although the present system has been described with respect to at least one illustrative example, many variations and modifications will become apparent to those skilled in the art upon reading the specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.