CA1157355A - Continuous monitor of the exposure to industrial gases and vapour contaminants - Google Patents
Continuous monitor of the exposure to industrial gases and vapour contaminantsInfo
- Publication number
- CA1157355A CA1157355A CA000354941A CA354941A CA1157355A CA 1157355 A CA1157355 A CA 1157355A CA 000354941 A CA000354941 A CA 000354941A CA 354941 A CA354941 A CA 354941A CA 1157355 A CA1157355 A CA 1157355A
- Authority
- CA
- Canada
- Prior art keywords
- tubular portion
- reagent
- elongate
- container
- membrane
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
- G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
- G01N21/78—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour
- G01N21/783—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour for analysing gases
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
- G01N31/22—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using chemical indicators
- G01N31/223—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using chemical indicators for investigating presence of specific gases or aerosols
- G01N31/224—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using chemical indicators for investigating presence of specific gases or aerosols for investigating presence of dangerous gases
Abstract
ABSTRACT OF THE DISCLOSURE
A device for continuously monitoring the exposure of a carrier of the device to an airborne contaminant comprises a tube filled with an inert packing and a reagent which changes colour upon contact with the contaminant to be monitored. The tube has an open end and a membrane closes that end, the membrane permitting diffusion of the contaminant therethrough. The length of the packing which changes colour is directly proportional to the time weighted average concentration of the contaminant to which the device and the carrier or wearer of that device has been exposed.
A device for continuously monitoring the exposure of a carrier of the device to an airborne contaminant comprises a tube filled with an inert packing and a reagent which changes colour upon contact with the contaminant to be monitored. The tube has an open end and a membrane closes that end, the membrane permitting diffusion of the contaminant therethrough. The length of the packing which changes colour is directly proportional to the time weighted average concentration of the contaminant to which the device and the carrier or wearer of that device has been exposed.
Description
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BACKGROUND OF THE INVENTION
This invention is concerned with a device for continuously monitoring the exposure of a carrier of the device to an airborne contaminant. The need to insure that workers in industrial environments are not subject to excessive dosages of dangerous gases and vapours is well known. To achieve this end in the past it has been the practice to provide a container of activated charcoal or other absorbent to be worn by a worker along with a pump which directs air through the container. At the end of the day, the charcoal would be removed and the contaminant which had been adsorbed upon it would be removed for subsequent and rather costly analysis, as for example by chromatography. This equipment was bulky and of course the analysis was not completed until, at best, days end and usually not until several days later, so that there was no immediate indication of the dosage to which a worker had been exposed.
In recent years a so-called passive monitor has been devised and is currently used which comprises a container of activated charcoal having one side closed by a membrane (e.g. of silicone rubber) through which contaminants diffuse to be adsorbed on the charcoal. This device was small and could conveniently be worn close to a worker's breathing zone.
Unlike classical dosimeters which use a pump to bring air sample into contact with a collection element or a detector, passive dosimeters rely on diffusion for this. Since the "diffusion" rate of a gas or vapour is very sensitive to the ~A`
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flow of air over and around the dosimeter, a membrane or other limiting resistance must be located between the bulk air and the collection element. The rate of mass transfer to the collection element is now controlled by the rate of diffusion or permeation across the membrane and the effect of face velocity past the dosimeter if effectively eliminated.
Passive dosimeters of gas or vapour exposure have clear advantages over the more classical methods of personal monitoring in the workplace. Cumbersome pumps and tubing are avoided, monitoring is less expensive and more reliable since neither calibration of a pump nor charging of a battery pack are needed. However, such dosimeters have the disadvantage of a need for follow-up analysis to obtain quantitative results.
This is particularly true for activated charcoal based passive monitors for which the adsorbed vapour must be desorbed in carbon disulphide for quantification by gas chromatography. Not only is there a significant delay (1 day to 1 week or more) in obtaining the result thereby, but also the cost of analysis is very high.
Widespread use of these devices is clearly hindered by both this cost and the inability to obtain the result immediately at the end of the worker shift, or even during the shift. The ability to inform the worker that he has exceeded his daily allowable dosage before his shift is actually finished, offers an interesting potential to control his exposure and therefore his health to a much finer degree.
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Gas chromatography is not the only method used to quantify the amount of gas or vapour collected by the passive dosimeters. A dedicated spectrophotolneter has been proposed for detecting NO, S02 or NH3, while spectrophotometers, specific ion electrodes or wet chemistry methods are necessary for other devices and the changing resistance of gold foil is the basis of a device for ~g detection. While the analytical methods may be simpler and quicker than gas chromatography, they still provide an additional cost and delay in quantifying worker exposure. A
recently developed CO monitor changes colour when the TLV
exposure is exceeded and is an initial attempt to address these limitations.
It is an object of the present invention to provide a device effective continuously to monitor the exposure of a carrier of the device to an airborne contaminant so that one may have at any time an immediate indication of the dosage to which the carrier has been exposed. The present invention also seeks to provide a method for continuously monitoring the exposure of a worker to an airborne contaminant.
According to one aspect of the present invention there is provided a device for continuously monitoring the exposure of a wearer of the device to an airborne contaminant, said device including an elongate transparent length-of-stain indicator means for providing a visual indication of the amount of airborne contaminant to which said device has been exposed, said length-of-stain indicator means comprising:
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(a) an air-impermeable elongate container comprising a transparent elongate tubular portion closed at one end thereof and having an end portion at an opposite end of the tubular portion, said end portion widening towards said opposite end to define an opening having a cross-sectional area greater than the cross-sectional area of the tubular portion, said elongate container being air-tight except at said opening;
(b) reagent means accommodated in said transparent elongate tubular portion for producing a colour change in response to exposure of said reagent means to said airborne contaminant, said colour change producing a stain in said reagent means observable as a length-of-colour stain extending along said elongate tubular portion as an indication of the amount of said airborne contaminant to which said device has been exposed; and (c) membrane means extending across and covering said opening for controlling diffusion from the atmosphere into said elongate container, said membrane means being permeable to said airborne contaminant to permit penetration of said airborne contaminant into said transparent elongate tubular portion and into contact with said reagent means, the membrane means, the end portion and the opposite end of the tubular portion defining an air space, said membrane means being separated from said transparent elongate tubular portion and from the reagent member by the air space.
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l 157355 Preferably the reagent is carried on a gel or other carrier or packing and, by changing colour upon exposure to the contaminant, indicates by the length of tube over which the reagent has changed colour the dosage to which a wearer of the device has been subject.
The material of the membrane and its size is selected so that the quantity of air passing through it and reaching the reagent during a normal working period is that which will, if the air is contaminated, produce a change in colour of the reagent over a length which is easily measured.
Further according to this invention there is provided a method of continuously monitoring the exposure of an individual to an airborne contaminant, said method comprising:
(i) attaching a device to a wearer, said device including an elongate transparent length-of-stain indicator means for providing a visual indication of the amount of airborne contaminant to which the device has been exposed, said indicator means comprising (a) an air-impermeable elongate container comprising a transparent elongate tubular portion closed at one end thereof and having an end portion at an opposite end of the tubular portion, said end portion widening from said opposite end to define an opening having a cross-sectional area greater than the cross-sectional area of the tubular portion, said elongate container being air-tight except at said opening, (b) reagent means ' ' ``` l 157~S
accommodated in said transparent elongate tubular portion for producing a colour change in response to exposure of said reagent means to said airborne contaminant, said colour change producing a stain in said reagent means observable as a length-of-colour stain extending along said elongate tubular portion as an indication of the amount of said airborne contaminant to which said device has been exposed, and (c) membrane means extending across and covering said opening for controlling diffusion from the atmosphere into said elongate container, said membrane means being permeable to said airborne contaminant to permit penetration of said airborne contaminant into said transparent elongate tubular portion and into contact with said reagent means, the membrane means, the end portion and the opposite end of the tubular portion defining an air space, said membrane means being separated from said transparent elongate tubular portion and from the reagent means by the air space; and (ii) checking the quantity of contaminant by observing the length-of-colour stain in said reagent means to derive an indication of the time weighted average concentration of the contaminant to which the individual has been exposed.
An embodiment of the invention as illustrated, schematically, in the accompanying drawing in which:
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- 1 1 ~j r~ 3 5 ~j Figure 1 is a cross-section of a device embodying to present invention;
Figure 2 is a cross-section view of an alternative embodiment of this invention; and Figure 3 comprises side and end views of a further embodiment of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The device in the drawings comprise a transparent tube 10 closed at one end 12 and open at opposite end 14 and having graduation or calibration markings 15. Within the tube there is inert packing 16 carrying a reagent responsive to a contaminant to be monitored by the device. Secured to the open end of the tube 10 is a bell-like structure 18 the larger end 20 of which is closed by a silicone rubber membrane or diaphragm 22.
In operation a worker carries the device in his pocket or pinned to his clothing as close as possible to his face, so that the device is in effect sampling or monitoring the atmosphere in the region where it is being breathed by the worker. AS the contaminant diffuses through the membrane 22 it reaches the reagent on the packing 16 and the gel changes colour progressively, as indicated by a stain front 17. ThuS, the distance represented by the length of the tube over which the reagent has changed colour is directly related to the quantity of contaminant passing through the membrane 22 and reaching the reagent.
Typical contaminants to be monitored and the reagents used in that monitoring are listed below:
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Contaminant Reagent carbon dioxide crystal violet/hydrazine benzene iodine pentoxide/sulphuric acid hydrogen sulphide heavy metal salts carbon monoxide* selenium dioxide/sulphuric acid vinyl chloride permanganate/o-toluidine ammonia acid/bromophenal blue etc.
*drying or precleanse layers are required to minimize interferences.
It will be recognized that the device of the present invention gives a continuous indication of the dosage of a contaminant to which a worker has been exposed.
Thus, the present passive dosimeter provides a continuous readout of the exposure. The accumulated dose is read as the length of coloured stain on the tube 10, specific to a particular gas or vapour.
The dosimeter is a combination of the gas indicator tube 10 and the membrane 22. The gas or vapour diffuses through the membrane to the colour change reagent dispersed on an appropriate support in the gas indicator tube 10. Reaction between the diffusing gas and these reagents causes the reagent on the support to change colour. As more gas or vapour diffuses into the indicator tube 10 more of the reagent changes colour, , , ~ , 5 $
with the volume of coloured reagent and hence the stain length related to the amount of gas or vapour to which the dosimeter has been exposed (i.e. the dose).
The membrane 22 should be large enough or have a sufficiently high permeability to permit sufficient gas to move through the membrane 22 to react with the colour change reagents. Silicone rubber has been found appropriate for CO , benzene and NO . The support should be able to retain sufficient colour change reagent yet not adsorb the diffusion gas. This is particularly important for the low concentration detectors (e.g. benzene) where adsorption of vapour without reaction is significant and essentially slows down or stops the movement of the stain down the gas indicator tube. Glass bead or clay supports are preferable to silica gel in these cases.
At high stain lengths, the calibration curve begins to level off. As the stain length increases, diffusion of the gas in the indicator tube 10 becomes limiting with a consequent reduction in the slope of the calibration curve. The indicator tube 10 should be packed with support in such a way as to maximize the diffusion coefficient in the tube 10. Alternative methods of supporting the reagents to increase the useful measurement range of the device are available.
Since the limitation to long stain lengths is the p~ck~d resistance to diffusion through a long tube ~a~e~ with solid support, means to increase the diffusion coefficient in the indicating layer will be greater as the stain length scale will ~ ;
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be expanded over a longer tube. Unfortunately, the obvious variation of support mesh size has a rather limited effect on the diffusion coefficient in the tube. Furthermore, very large particles are capable of retaining only very small amounts of colour change reagents and are therefore not practical.
Alternatively short lengths of capillary tubes (e.g. glass) can be used as supports for the colour change reagents. Provided s sufficient loading is obtained, the diffusion coefficient be . identical to the relatively high diffusion coefficient in air.
The specificity of the dosimeter is limited by the specificity of the colour change chemistry. For example, the ; benzene dosimeter is essentially an aromatic hydrocarbon detector with interference expected from toluene and xylene.
The presence of the membrane with its own permselectivity towards lower molecular weight compounds minimizes this problem.
Another limitation of the colour change chemistry is its sensitivity to extraneous effects, most especially humidity. ThiS is particularly so for NO . For conventional gas indicator tubes used to measure ambient concentration, a drying layer must be added to the tube to control the humidity of the ambient air.
Additional precleanse or drying layers, when necessary, cannot be incorporated as additional lengths of the tube between -the membrane and the indicator tube 10 because of the relationship between tube length and the rate of diffusion in the tube. Any additional resistance between the indicating ', , _ g _ i ~A:
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layer and the membrane only serves to shorten the actual coloured stain and make the device more difficult to read.
Alternatively, the configuration of Figure 2 can be used. In Figure 2, parts which correspond to those of Figure 1 have been indicated by the same reference numerals. In this case, a drying or precleanse layer 24 is provided as a thin, wide layer between the membrane and the indicating tube, the layer 24 being retained by a glass wool layer 26. Provided sufficient adsorptive or reaction capacity is present in the layer 24, drying or precleaning of the diffusing vapour can be achieved without significantly lengthening the tube 10 and compromising the stain length relationship to accumulated dose. In addition, these layers must be sufficiently specific, so that inadvertent adsorption of the test gas does not occur.
15Assessment of each device is essentially achieved by - the preparation of a calibration curve relating time weighted average cocentration (e.g. 8 hr) to length. The dosimeters are exposed to a constant concentration atmosphere in a suitable chamber which is continually flushed with the gas-in-air mixture of the desired concentration. Since these mixtures can be problematic, the gas concentration in the chamber is periodically or continuously measured.
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Silica gel, clay (Chromosorb/W) and glass beads (all 40-60 mesh) are appropriate supports for the indicating ; 25 precleanse, and/or drying layers. Particular attention must be given to the minimization of adsorption of the test gas at low ' ~ .
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The reagents are dispersed on the support, generally by loading small volumes of reagent solution on to relatively large . amounts of solid, followed by drying in a rotary evaporator Although the required amount of primary colour change reagent ~, can normally be calculated, the amounts of the other reagents must be determined by trial and error. Changes in the mechanism of reaction from the homogeneous to the heterogeneous systems ~ typically complicates the chemistry of the reactions.
- 10 The presence of the large area membrane 22 at the end of the small diameter tube 10 in Figure 1 is probably not the most convenient configuration of this device. Folding of the membrane into a "concertina" shape with the same outside diameter as the tube would be one improvement. Alternatively, as shown in Figure 3, a disk-shaped badge comprising an impermeable container 27 with diffusion in a radial direction through a membrane 28, an air space 29 and an annular body 30 of the reagen~ of the packing might yield a more compact device, although the "stain length" (now read as the radius of a coloured ring defined by a stain front 31) would be even more sensitive to the limitation of diffusion through the reagent.
The development of this passive monitor with instant readout will facilitate the personal monitoring of gases and vapours in the workplace. The device is much less expensive and easier and more convenient to use than existing devices. It is a device with which workers themselves can monitor their own ,, ~;A 11 exposure. It will make them more aware of their environment and encourage them to be more concerned with their health on the job. It is a device which is sufficiently inexpensive to permit ,:
more widespread monitoring than is currently economically feasible. Problem areas can be identified more readily and with greater reliability. Government inspectors will be able to assess the in-plant exposure essentially during a visit and the need for follow up visits can be reduced.
In general, this device will place industrial hygiene monitoring of gas and vapour exposure on a more routine and widespread level. Consequently the incidence of occupational desease will decrease as the danger of unknown exposure is minimized.
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SUPPLEMENTARY DISCLOSURE
Referring again to Figure 1, for detecting H S, lead chloride has been found to be a satisfactory reagent when used in the proportion of 7.10 multiplied by 10 - 7 moles per gram of inert packing 16, while for detecting benzene, 10 - 5 moles of iodine pentoxide in 96% sulfuric acid added to each 2.5 grams of the inert packing 16 has been found to give satisfactory results.
The inert packing 16, preferably an acid washed diatomaceous earth sold under the trademark CHROMOSORB W, mixed with the reagent until the packing is free flowing, is added to the tube 10, which is a glass tube with an inside diameter of 6mm., and vibrated to obtain a packed density of 0,254 grams per cubic centimeter, and is kept in place by a piece 15 of glass fabric and an overlying piece 17 of wire mesh inserted into the open end 14 of the glass tube 10.
The membrane or diaphragm 22 is of silicone rubber having a thickness of 5 mils. and manufactured by Sci-Med Inc., of Minneapolis, Minnesota. The membrane 22 is glued to the structure 18 by an RTV adhesive.
Figures 4 to 9 show diagrammatic views in cross-section through six further dosimeters embodying the present invention.
Figure 4 shows a modification of the device of Figure 1, in which modification the bell-like structure has been replaced by a glass adaptor, indicated generally by reference numeral 44, comprising a cylindrical portion 42 and end portion 44, on which the membrane 22 is provided.
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In addition, the glass tube lO is provided with a spring metal clip 45 to enable the dosimeter to be clipped, e.g.
to the lapel of the wearer's shirt.
The contents of the tube 10 are the same as those described hereinabove with reference to Figure l.
In the embodiments of the invention illustrated in Figure 5 of the drawings, the packing and reagent are contained in a glass tube lOa which is open at it's lower end only and which is supported by means of annular plastic spacers 46 within a protective houslng indicated generally by reference numeral 47, which may be made of glass but which is preferably made of a breakage-resistant transparent plastics material. The housing 47 has a cylindrical wall 48 and a closed end 49, the opposite end of the housing 47 defining an opening which is closed by diaphragm 22a.
The material of the diaphragm 22a and the contents of the tube lOa correspond to those of the diaphragm 22 and the tube lO of Figure 1.
As indicated above, diffusion of the gas along the indica~or tube becomes limiting as the stain length increases, the limitation to long stain lengths being the resistance to diffusion through the tube packed with the solid packing.
Hence, in order to increase the precision and ease of reading of the above device, the cross-sectional area of the indicator tube may be varied, so as to decrease in the direction of diffusion of the contaminant.
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For example, Figure 6 diagramatically illustrates a dosimeter having a container, indicated generally by reference numeral 49, which is made of glass and which has an exponentially curved wall 50, the container 49 being closed by a silicone rubber membrane 51 at an open end thereof and containing a packing and reagent such as those described above.
The embodiment illustrated in Figure 7 is similar to that of Figure 6 except that, in this case, the wall of the container, which is indicated by reference numeral 53, is conical.
Figure 8 shows another possible configuration for the indicator tube and it's protective housing. In this case, the -~
tube, which is indicated by reference numeral 55, opens at it's upper end into a frusto-conical adaptor 56, having an open upper end coincident with the open upper end of the protective housing, which is indicated by reference numeral 57 and comprises a transparent plastics material, the open upper ends of the adaptor 56 and the housing 57 being closed by a silicone rubber membrane 58. 'r Figure 9 shows an embodiment in which a glass indicator tube 60, which is cylindrical and which contains the same packing, reagent etc. as the tube 10 of Figure 1, is provided at it's upper end with a cylindrical support structure 61, e.g.
wire mesh, which is provided within and supports a cylindrical silicone rubber diaphragm 62.
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BACKGROUND OF THE INVENTION
This invention is concerned with a device for continuously monitoring the exposure of a carrier of the device to an airborne contaminant. The need to insure that workers in industrial environments are not subject to excessive dosages of dangerous gases and vapours is well known. To achieve this end in the past it has been the practice to provide a container of activated charcoal or other absorbent to be worn by a worker along with a pump which directs air through the container. At the end of the day, the charcoal would be removed and the contaminant which had been adsorbed upon it would be removed for subsequent and rather costly analysis, as for example by chromatography. This equipment was bulky and of course the analysis was not completed until, at best, days end and usually not until several days later, so that there was no immediate indication of the dosage to which a worker had been exposed.
In recent years a so-called passive monitor has been devised and is currently used which comprises a container of activated charcoal having one side closed by a membrane (e.g. of silicone rubber) through which contaminants diffuse to be adsorbed on the charcoal. This device was small and could conveniently be worn close to a worker's breathing zone.
Unlike classical dosimeters which use a pump to bring air sample into contact with a collection element or a detector, passive dosimeters rely on diffusion for this. Since the "diffusion" rate of a gas or vapour is very sensitive to the ~A`
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flow of air over and around the dosimeter, a membrane or other limiting resistance must be located between the bulk air and the collection element. The rate of mass transfer to the collection element is now controlled by the rate of diffusion or permeation across the membrane and the effect of face velocity past the dosimeter if effectively eliminated.
Passive dosimeters of gas or vapour exposure have clear advantages over the more classical methods of personal monitoring in the workplace. Cumbersome pumps and tubing are avoided, monitoring is less expensive and more reliable since neither calibration of a pump nor charging of a battery pack are needed. However, such dosimeters have the disadvantage of a need for follow-up analysis to obtain quantitative results.
This is particularly true for activated charcoal based passive monitors for which the adsorbed vapour must be desorbed in carbon disulphide for quantification by gas chromatography. Not only is there a significant delay (1 day to 1 week or more) in obtaining the result thereby, but also the cost of analysis is very high.
Widespread use of these devices is clearly hindered by both this cost and the inability to obtain the result immediately at the end of the worker shift, or even during the shift. The ability to inform the worker that he has exceeded his daily allowable dosage before his shift is actually finished, offers an interesting potential to control his exposure and therefore his health to a much finer degree.
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Gas chromatography is not the only method used to quantify the amount of gas or vapour collected by the passive dosimeters. A dedicated spectrophotolneter has been proposed for detecting NO, S02 or NH3, while spectrophotometers, specific ion electrodes or wet chemistry methods are necessary for other devices and the changing resistance of gold foil is the basis of a device for ~g detection. While the analytical methods may be simpler and quicker than gas chromatography, they still provide an additional cost and delay in quantifying worker exposure. A
recently developed CO monitor changes colour when the TLV
exposure is exceeded and is an initial attempt to address these limitations.
It is an object of the present invention to provide a device effective continuously to monitor the exposure of a carrier of the device to an airborne contaminant so that one may have at any time an immediate indication of the dosage to which the carrier has been exposed. The present invention also seeks to provide a method for continuously monitoring the exposure of a worker to an airborne contaminant.
According to one aspect of the present invention there is provided a device for continuously monitoring the exposure of a wearer of the device to an airborne contaminant, said device including an elongate transparent length-of-stain indicator means for providing a visual indication of the amount of airborne contaminant to which said device has been exposed, said length-of-stain indicator means comprising:
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(a) an air-impermeable elongate container comprising a transparent elongate tubular portion closed at one end thereof and having an end portion at an opposite end of the tubular portion, said end portion widening towards said opposite end to define an opening having a cross-sectional area greater than the cross-sectional area of the tubular portion, said elongate container being air-tight except at said opening;
(b) reagent means accommodated in said transparent elongate tubular portion for producing a colour change in response to exposure of said reagent means to said airborne contaminant, said colour change producing a stain in said reagent means observable as a length-of-colour stain extending along said elongate tubular portion as an indication of the amount of said airborne contaminant to which said device has been exposed; and (c) membrane means extending across and covering said opening for controlling diffusion from the atmosphere into said elongate container, said membrane means being permeable to said airborne contaminant to permit penetration of said airborne contaminant into said transparent elongate tubular portion and into contact with said reagent means, the membrane means, the end portion and the opposite end of the tubular portion defining an air space, said membrane means being separated from said transparent elongate tubular portion and from the reagent member by the air space.
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l 157355 Preferably the reagent is carried on a gel or other carrier or packing and, by changing colour upon exposure to the contaminant, indicates by the length of tube over which the reagent has changed colour the dosage to which a wearer of the device has been subject.
The material of the membrane and its size is selected so that the quantity of air passing through it and reaching the reagent during a normal working period is that which will, if the air is contaminated, produce a change in colour of the reagent over a length which is easily measured.
Further according to this invention there is provided a method of continuously monitoring the exposure of an individual to an airborne contaminant, said method comprising:
(i) attaching a device to a wearer, said device including an elongate transparent length-of-stain indicator means for providing a visual indication of the amount of airborne contaminant to which the device has been exposed, said indicator means comprising (a) an air-impermeable elongate container comprising a transparent elongate tubular portion closed at one end thereof and having an end portion at an opposite end of the tubular portion, said end portion widening from said opposite end to define an opening having a cross-sectional area greater than the cross-sectional area of the tubular portion, said elongate container being air-tight except at said opening, (b) reagent means ' ' ``` l 157~S
accommodated in said transparent elongate tubular portion for producing a colour change in response to exposure of said reagent means to said airborne contaminant, said colour change producing a stain in said reagent means observable as a length-of-colour stain extending along said elongate tubular portion as an indication of the amount of said airborne contaminant to which said device has been exposed, and (c) membrane means extending across and covering said opening for controlling diffusion from the atmosphere into said elongate container, said membrane means being permeable to said airborne contaminant to permit penetration of said airborne contaminant into said transparent elongate tubular portion and into contact with said reagent means, the membrane means, the end portion and the opposite end of the tubular portion defining an air space, said membrane means being separated from said transparent elongate tubular portion and from the reagent means by the air space; and (ii) checking the quantity of contaminant by observing the length-of-colour stain in said reagent means to derive an indication of the time weighted average concentration of the contaminant to which the individual has been exposed.
An embodiment of the invention as illustrated, schematically, in the accompanying drawing in which:
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- 1 1 ~j r~ 3 5 ~j Figure 1 is a cross-section of a device embodying to present invention;
Figure 2 is a cross-section view of an alternative embodiment of this invention; and Figure 3 comprises side and end views of a further embodiment of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The device in the drawings comprise a transparent tube 10 closed at one end 12 and open at opposite end 14 and having graduation or calibration markings 15. Within the tube there is inert packing 16 carrying a reagent responsive to a contaminant to be monitored by the device. Secured to the open end of the tube 10 is a bell-like structure 18 the larger end 20 of which is closed by a silicone rubber membrane or diaphragm 22.
In operation a worker carries the device in his pocket or pinned to his clothing as close as possible to his face, so that the device is in effect sampling or monitoring the atmosphere in the region where it is being breathed by the worker. AS the contaminant diffuses through the membrane 22 it reaches the reagent on the packing 16 and the gel changes colour progressively, as indicated by a stain front 17. ThuS, the distance represented by the length of the tube over which the reagent has changed colour is directly related to the quantity of contaminant passing through the membrane 22 and reaching the reagent.
Typical contaminants to be monitored and the reagents used in that monitoring are listed below:
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Contaminant Reagent carbon dioxide crystal violet/hydrazine benzene iodine pentoxide/sulphuric acid hydrogen sulphide heavy metal salts carbon monoxide* selenium dioxide/sulphuric acid vinyl chloride permanganate/o-toluidine ammonia acid/bromophenal blue etc.
*drying or precleanse layers are required to minimize interferences.
It will be recognized that the device of the present invention gives a continuous indication of the dosage of a contaminant to which a worker has been exposed.
Thus, the present passive dosimeter provides a continuous readout of the exposure. The accumulated dose is read as the length of coloured stain on the tube 10, specific to a particular gas or vapour.
The dosimeter is a combination of the gas indicator tube 10 and the membrane 22. The gas or vapour diffuses through the membrane to the colour change reagent dispersed on an appropriate support in the gas indicator tube 10. Reaction between the diffusing gas and these reagents causes the reagent on the support to change colour. As more gas or vapour diffuses into the indicator tube 10 more of the reagent changes colour, , , ~ , 5 $
with the volume of coloured reagent and hence the stain length related to the amount of gas or vapour to which the dosimeter has been exposed (i.e. the dose).
The membrane 22 should be large enough or have a sufficiently high permeability to permit sufficient gas to move through the membrane 22 to react with the colour change reagents. Silicone rubber has been found appropriate for CO , benzene and NO . The support should be able to retain sufficient colour change reagent yet not adsorb the diffusion gas. This is particularly important for the low concentration detectors (e.g. benzene) where adsorption of vapour without reaction is significant and essentially slows down or stops the movement of the stain down the gas indicator tube. Glass bead or clay supports are preferable to silica gel in these cases.
At high stain lengths, the calibration curve begins to level off. As the stain length increases, diffusion of the gas in the indicator tube 10 becomes limiting with a consequent reduction in the slope of the calibration curve. The indicator tube 10 should be packed with support in such a way as to maximize the diffusion coefficient in the tube 10. Alternative methods of supporting the reagents to increase the useful measurement range of the device are available.
Since the limitation to long stain lengths is the p~ck~d resistance to diffusion through a long tube ~a~e~ with solid support, means to increase the diffusion coefficient in the indicating layer will be greater as the stain length scale will ~ ;
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be expanded over a longer tube. Unfortunately, the obvious variation of support mesh size has a rather limited effect on the diffusion coefficient in the tube. Furthermore, very large particles are capable of retaining only very small amounts of colour change reagents and are therefore not practical.
Alternatively short lengths of capillary tubes (e.g. glass) can be used as supports for the colour change reagents. Provided s sufficient loading is obtained, the diffusion coefficient be . identical to the relatively high diffusion coefficient in air.
The specificity of the dosimeter is limited by the specificity of the colour change chemistry. For example, the ; benzene dosimeter is essentially an aromatic hydrocarbon detector with interference expected from toluene and xylene.
The presence of the membrane with its own permselectivity towards lower molecular weight compounds minimizes this problem.
Another limitation of the colour change chemistry is its sensitivity to extraneous effects, most especially humidity. ThiS is particularly so for NO . For conventional gas indicator tubes used to measure ambient concentration, a drying layer must be added to the tube to control the humidity of the ambient air.
Additional precleanse or drying layers, when necessary, cannot be incorporated as additional lengths of the tube between -the membrane and the indicator tube 10 because of the relationship between tube length and the rate of diffusion in the tube. Any additional resistance between the indicating ', , _ g _ i ~A:
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layer and the membrane only serves to shorten the actual coloured stain and make the device more difficult to read.
Alternatively, the configuration of Figure 2 can be used. In Figure 2, parts which correspond to those of Figure 1 have been indicated by the same reference numerals. In this case, a drying or precleanse layer 24 is provided as a thin, wide layer between the membrane and the indicating tube, the layer 24 being retained by a glass wool layer 26. Provided sufficient adsorptive or reaction capacity is present in the layer 24, drying or precleaning of the diffusing vapour can be achieved without significantly lengthening the tube 10 and compromising the stain length relationship to accumulated dose. In addition, these layers must be sufficiently specific, so that inadvertent adsorption of the test gas does not occur.
15Assessment of each device is essentially achieved by - the preparation of a calibration curve relating time weighted average cocentration (e.g. 8 hr) to length. The dosimeters are exposed to a constant concentration atmosphere in a suitable chamber which is continually flushed with the gas-in-air mixture of the desired concentration. Since these mixtures can be problematic, the gas concentration in the chamber is periodically or continuously measured.
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Silica gel, clay (Chromosorb/W) and glass beads (all 40-60 mesh) are appropriate supports for the indicating ; 25 precleanse, and/or drying layers. Particular attention must be given to the minimization of adsorption of the test gas at low ' ~ .
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The reagents are dispersed on the support, generally by loading small volumes of reagent solution on to relatively large . amounts of solid, followed by drying in a rotary evaporator Although the required amount of primary colour change reagent ~, can normally be calculated, the amounts of the other reagents must be determined by trial and error. Changes in the mechanism of reaction from the homogeneous to the heterogeneous systems ~ typically complicates the chemistry of the reactions.
- 10 The presence of the large area membrane 22 at the end of the small diameter tube 10 in Figure 1 is probably not the most convenient configuration of this device. Folding of the membrane into a "concertina" shape with the same outside diameter as the tube would be one improvement. Alternatively, as shown in Figure 3, a disk-shaped badge comprising an impermeable container 27 with diffusion in a radial direction through a membrane 28, an air space 29 and an annular body 30 of the reagen~ of the packing might yield a more compact device, although the "stain length" (now read as the radius of a coloured ring defined by a stain front 31) would be even more sensitive to the limitation of diffusion through the reagent.
The development of this passive monitor with instant readout will facilitate the personal monitoring of gases and vapours in the workplace. The device is much less expensive and easier and more convenient to use than existing devices. It is a device with which workers themselves can monitor their own ,, ~;A 11 exposure. It will make them more aware of their environment and encourage them to be more concerned with their health on the job. It is a device which is sufficiently inexpensive to permit ,:
more widespread monitoring than is currently economically feasible. Problem areas can be identified more readily and with greater reliability. Government inspectors will be able to assess the in-plant exposure essentially during a visit and the need for follow up visits can be reduced.
In general, this device will place industrial hygiene monitoring of gas and vapour exposure on a more routine and widespread level. Consequently the incidence of occupational desease will decrease as the danger of unknown exposure is minimized.
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SUPPLEMENTARY DISCLOSURE
Referring again to Figure 1, for detecting H S, lead chloride has been found to be a satisfactory reagent when used in the proportion of 7.10 multiplied by 10 - 7 moles per gram of inert packing 16, while for detecting benzene, 10 - 5 moles of iodine pentoxide in 96% sulfuric acid added to each 2.5 grams of the inert packing 16 has been found to give satisfactory results.
The inert packing 16, preferably an acid washed diatomaceous earth sold under the trademark CHROMOSORB W, mixed with the reagent until the packing is free flowing, is added to the tube 10, which is a glass tube with an inside diameter of 6mm., and vibrated to obtain a packed density of 0,254 grams per cubic centimeter, and is kept in place by a piece 15 of glass fabric and an overlying piece 17 of wire mesh inserted into the open end 14 of the glass tube 10.
The membrane or diaphragm 22 is of silicone rubber having a thickness of 5 mils. and manufactured by Sci-Med Inc., of Minneapolis, Minnesota. The membrane 22 is glued to the structure 18 by an RTV adhesive.
Figures 4 to 9 show diagrammatic views in cross-section through six further dosimeters embodying the present invention.
Figure 4 shows a modification of the device of Figure 1, in which modification the bell-like structure has been replaced by a glass adaptor, indicated generally by reference numeral 44, comprising a cylindrical portion 42 and end portion 44, on which the membrane 22 is provided.
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In addition, the glass tube lO is provided with a spring metal clip 45 to enable the dosimeter to be clipped, e.g.
to the lapel of the wearer's shirt.
The contents of the tube 10 are the same as those described hereinabove with reference to Figure l.
In the embodiments of the invention illustrated in Figure 5 of the drawings, the packing and reagent are contained in a glass tube lOa which is open at it's lower end only and which is supported by means of annular plastic spacers 46 within a protective houslng indicated generally by reference numeral 47, which may be made of glass but which is preferably made of a breakage-resistant transparent plastics material. The housing 47 has a cylindrical wall 48 and a closed end 49, the opposite end of the housing 47 defining an opening which is closed by diaphragm 22a.
The material of the diaphragm 22a and the contents of the tube lOa correspond to those of the diaphragm 22 and the tube lO of Figure 1.
As indicated above, diffusion of the gas along the indica~or tube becomes limiting as the stain length increases, the limitation to long stain lengths being the resistance to diffusion through the tube packed with the solid packing.
Hence, in order to increase the precision and ease of reading of the above device, the cross-sectional area of the indicator tube may be varied, so as to decrease in the direction of diffusion of the contaminant.
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For example, Figure 6 diagramatically illustrates a dosimeter having a container, indicated generally by reference numeral 49, which is made of glass and which has an exponentially curved wall 50, the container 49 being closed by a silicone rubber membrane 51 at an open end thereof and containing a packing and reagent such as those described above.
The embodiment illustrated in Figure 7 is similar to that of Figure 6 except that, in this case, the wall of the container, which is indicated by reference numeral 53, is conical.
Figure 8 shows another possible configuration for the indicator tube and it's protective housing. In this case, the -~
tube, which is indicated by reference numeral 55, opens at it's upper end into a frusto-conical adaptor 56, having an open upper end coincident with the open upper end of the protective housing, which is indicated by reference numeral 57 and comprises a transparent plastics material, the open upper ends of the adaptor 56 and the housing 57 being closed by a silicone rubber membrane 58. 'r Figure 9 shows an embodiment in which a glass indicator tube 60, which is cylindrical and which contains the same packing, reagent etc. as the tube 10 of Figure 1, is provided at it's upper end with a cylindrical support structure 61, e.g.
wire mesh, which is provided within and supports a cylindrical silicone rubber diaphragm 62.
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Claims (11)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A device for continuously monitoring the exposure of a wearer of the device to an airborne contaminant, said device including an elongate transparent length-of-stain indicator means for providing a visual indication of the amount of airborne contaminant to which said device has been exposed, said length-of-stain indicator means comprising:
(a) an air-impermeable elongate container comprising a transparent elongate tubular portion closed at one end thereof and having an end portion at an opposite end of the tubular portion, said end portion widening towards said opposite end to define an opening having a cross-sectional area greater than the cross-sectional area of the tubular portion, said elongate container being air-tight except at said opening;
(b) reagent means accommodated in said transparent elongate tubular portion for producing a colour change in response to exposure of said reagent means to said airborne contaminant, said colour change producing a stain in said reagent means observable as a length-of-colour stain extending along said elongate tubular portion as an indication of the amount of said airborne contaminant to which said device has been exposed; and (c) membrane means extending across and covering said opening for controlling diffusion from the atmosphere into said elongate container, said membrane means being permeable to said airborne contaminant to permit penetration of said airborne contaminant into said transparent elongate tubular portion and into contact with said reagent means, the membrane means, the end portion and the opposite end of the tubular portion defining an air space, said membrane means being separated from said transparent elongate tubular portion and from the reagent member by the air space.
(a) an air-impermeable elongate container comprising a transparent elongate tubular portion closed at one end thereof and having an end portion at an opposite end of the tubular portion, said end portion widening towards said opposite end to define an opening having a cross-sectional area greater than the cross-sectional area of the tubular portion, said elongate container being air-tight except at said opening;
(b) reagent means accommodated in said transparent elongate tubular portion for producing a colour change in response to exposure of said reagent means to said airborne contaminant, said colour change producing a stain in said reagent means observable as a length-of-colour stain extending along said elongate tubular portion as an indication of the amount of said airborne contaminant to which said device has been exposed; and (c) membrane means extending across and covering said opening for controlling diffusion from the atmosphere into said elongate container, said membrane means being permeable to said airborne contaminant to permit penetration of said airborne contaminant into said transparent elongate tubular portion and into contact with said reagent means, the membrane means, the end portion and the opposite end of the tubular portion defining an air space, said membrane means being separated from said transparent elongate tubular portion and from the reagent member by the air space.
2. A device as claimed in claim 1, further comprising means in said container for supporting said reagent means.
3. A device as claimed in claim 1 wherein drying means is provided between the membrane and the reagent means in the elongate tubular portion.
4. A device as claimed in claim 3 wherein the drying means is a thin layer of hygroscopic material extending substantially across the width of the end portion and being of a greater cross-sectional area than the end portion of the elongate tubular portion.
5. A device as claimed in claim 3 or claim 4 wherein the drying means is supported by a fibrous layer, the fibrous layer and the drying layer being substantially non-adsorbent to said airborne contaminant.
6. A device as claimed in claim 1 wherein spaced markings are provided along the length of the container to permit measurement of the colour change of the reagent in response to exposure to said airborne contaminant.
7. A method of continuously monitoring the exposure of an individual to an airborne contaminant, said method comprising:
(i) attaching a device to a wearer, said device including an elongate transparent length-of-stain indicator means for providing a visual indication of the amount of airborne contaminant to which the device has been exposed, said indicator means comprising (a) an air-impermeable elongate container comprising a transparent elongate tubular portion closed at one end thereof and having an end portion at an opposite end of the tubular portion, said end portion widening from said opposite end to define an opening having a cross-sectional area greater than the cross-sectional area of the tubular portion, said elongate container being air-tight except at said opening, (b) reagent means accommodated in said transparent elongate tubular portion for producing a colour change in response to exposure of said reagent means to said airborne contaminant, said colour change producing a stain in said reagent means observable as a length-of-colour stain extending along said elongate tubular portion as an indication of the amount of said airborne contaminant to which said device has been exposed, and (c) membrane means extending across and covering said opening for controlling diffusion from the atmosphere into said elongate container, said membrane means being permeable to said airborne contaminant to permit penetration of said airborne contaminant into said transparent elongate tubular portion and into contact with said reagent means, the membrane means, the end portion and the opposite end of the tubular portion defining an air space, said membrane means being separated from said transparent elongate tubular portion and from the reagent means by the air space; and (ii) checking the quantity of contaminant by observing the length-of-colour stain in said reagent means to derive an indication of the time weighted average concentration of the contaminant to which the individual has been exposed.
CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE
(i) attaching a device to a wearer, said device including an elongate transparent length-of-stain indicator means for providing a visual indication of the amount of airborne contaminant to which the device has been exposed, said indicator means comprising (a) an air-impermeable elongate container comprising a transparent elongate tubular portion closed at one end thereof and having an end portion at an opposite end of the tubular portion, said end portion widening from said opposite end to define an opening having a cross-sectional area greater than the cross-sectional area of the tubular portion, said elongate container being air-tight except at said opening, (b) reagent means accommodated in said transparent elongate tubular portion for producing a colour change in response to exposure of said reagent means to said airborne contaminant, said colour change producing a stain in said reagent means observable as a length-of-colour stain extending along said elongate tubular portion as an indication of the amount of said airborne contaminant to which said device has been exposed, and (c) membrane means extending across and covering said opening for controlling diffusion from the atmosphere into said elongate container, said membrane means being permeable to said airborne contaminant to permit penetration of said airborne contaminant into said transparent elongate tubular portion and into contact with said reagent means, the membrane means, the end portion and the opposite end of the tubular portion defining an air space, said membrane means being separated from said transparent elongate tubular portion and from the reagent means by the air space; and (ii) checking the quantity of contaminant by observing the length-of-colour stain in said reagent means to derive an indication of the time weighted average concentration of the contaminant to which the individual has been exposed.
CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE
8. A device as claimed in claim 1, further comprising a transparent protective housing surrounding the container, the housing defining an opening through which the interior of the housing communicates with the atmosphere, and means supporting the container when the housing at a spacing from the housing, the membrane means extending across and covering the housing opening.
9. A device as claimed in claim 8, wherein the protecting housing surrounding the container defines an opening substantially coincident with the container opening.
10. A device as claimed in claim 1, wherein said elongate transparent indicator means has a cross-section which decreases along the length of the container, from the opening.
11. A device as claimed in claim 1, wherein said container is tubular, said opening being provided at one end thereof, and said membrane means is of tubular shape and extends from said opening, means being provided within said membrane means for supporting said membrane means in its tubular shape.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000354941A CA1157355A (en) | 1980-06-26 | 1980-06-26 | Continuous monitor of the exposure to industrial gases and vapour contaminants |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000354941A CA1157355A (en) | 1980-06-26 | 1980-06-26 | Continuous monitor of the exposure to industrial gases and vapour contaminants |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1157355A true CA1157355A (en) | 1983-11-22 |
Family
ID=4117285
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000354941A Expired CA1157355A (en) | 1980-06-26 | 1980-06-26 | Continuous monitor of the exposure to industrial gases and vapour contaminants |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1157355A (en) |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0202423A1 (en) * | 1985-04-10 | 1986-11-26 | Drägerwerk Aktiengesellschaft | Portable gas dosimeter |
| FR2622011A1 (en) * | 1987-10-17 | 1989-04-21 | Draegerwerk Ag | BROADCAST COLLECTOR |
| FR2624609A1 (en) * | 1987-12-09 | 1989-06-16 | Draegerwerk Ag | COLORIMETRIC TEST TUBE |
| WO1991012527A1 (en) * | 1990-02-08 | 1991-08-22 | Alcan International Limited | Fluid detection device |
| WO1999002986A1 (en) * | 1997-07-11 | 1999-01-21 | Donaldson Company, Inc. | Airborne contaminant indicator |
| US6187596B1 (en) | 1997-07-11 | 2001-02-13 | Donaldson Company, Inc. | Airborne contaminant indicator |
| JP2004163370A (en) * | 2002-11-15 | 2004-06-10 | Riken Keiki Co Ltd | Adapter for measuring high concentration gas |
-
1980
- 1980-06-26 CA CA000354941A patent/CA1157355A/en not_active Expired
Cited By (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0202423A1 (en) * | 1985-04-10 | 1986-11-26 | Drägerwerk Aktiengesellschaft | Portable gas dosimeter |
| FR2622011A1 (en) * | 1987-10-17 | 1989-04-21 | Draegerwerk Ag | BROADCAST COLLECTOR |
| DE3735307A1 (en) * | 1987-10-17 | 1989-04-27 | Draegerwerk Ag | DIFFUSION COLLECTOR |
| FR2624609A1 (en) * | 1987-12-09 | 1989-06-16 | Draegerwerk Ag | COLORIMETRIC TEST TUBE |
| DE3741664C1 (en) * | 1987-12-09 | 1989-08-10 | Draegerwerk Ag | Colorimetric test tube |
| GB2213585A (en) * | 1987-12-09 | 1989-08-16 | Draegerwerk Ag | Colorimetric test tube |
| US5000919A (en) * | 1987-12-09 | 1991-03-19 | Dragerwerk A.G. | Testing tube construction for testing gases which are dissolved in liquids and a method of making the same |
| GB2213585B (en) * | 1987-12-09 | 1991-07-31 | Draegerwerk Ag | Colorimetric test tube |
| WO1991012527A1 (en) * | 1990-02-08 | 1991-08-22 | Alcan International Limited | Fluid detection device |
| US5310525A (en) * | 1990-02-08 | 1994-05-10 | Whatman Scientific Limited | Fluid detection device |
| WO1999002986A1 (en) * | 1997-07-11 | 1999-01-21 | Donaldson Company, Inc. | Airborne contaminant indicator |
| US5976467A (en) * | 1997-07-11 | 1999-11-02 | Donaldson Company, Inc. | Airborne contaminant indicator |
| US6187596B1 (en) | 1997-07-11 | 2001-02-13 | Donaldson Company, Inc. | Airborne contaminant indicator |
| JP2004163370A (en) * | 2002-11-15 | 2004-06-10 | Riken Keiki Co Ltd | Adapter for measuring high concentration gas |
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