NL8102892A - DOSE METER FOR GASEOUS POLLUTANTS. - Google Patents

Description

N.0. 30,179 1

Dosimeter for gaseous pollutants.

! The invention relates to a personal dosimeter for registering gaseous pollutants in the atmosphere. More particularly, the invention relates to a dosimeter capable of collecting an amount of impurity proportional to its average atmospheric concentration to determine the integrated level of contamination exposure.

As a result of increasing health concerns for workers exposed to harmful air pollution, it has become necessary to monitor the concentration of pollutants in the air. A development for this purpose includes a fairly large air pump that pumps air to be sampled through a filter that captures contaminant particles. This is clearly ineffective for monitoring gaseous contaminants and is not accurate even for particles to determine the concentration of particles in the sampled atmosphere.

Personal sampling devices worn by individual workers who passively collect the contaminants; have also been used. For example, a device is described in II; "American Industrial Hygiene Association Journal", volume 34, pages 20 78-81 (1973), which uses the molecular diffusion of the monitored gas to collect the sample. This device and other similar plunge tubes are often difficult to use since their design and sensitive construction require that they always be properly oriented to accurately sample the atmosphere and to disrupt the sampling mechanism within prevent the tube.

Therefore, there remains a need for a personal dosimeter that simply but accurately collects gaseous contaminants proportional to their average atmospheric concentration.

According to the invention, a personal dosimeter j is provided for collecting a gaseous pollutant proportional to its average ambient concentration during the collection time, the dosimeter basically comprising a closed container, a gaseous pollutant collection medium within the container; 35 a diffusion device which forms part of the boundary of said container, which device contains a number of through channels, through which the gaseous pollution can diffuse from the atmosphere to | the interior space of the container, which channels each have a ratio: 81028

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2j have a length to diameter of at least 3 and form the only connection i between the atmosphere and the interior space of the container; and a porous water-repellent inert film covering the internal openings of said channels.

The invention will be explained in more detail below with reference to the drawing. In the drawing: Fig. 1 shows an enlarged perspective view of a diffusion device useful in the invention.

Fig. 2 is a top plan view of a gaseous pollutant dosimeter using the diffuser of FIG.

Fig. 3 is a perspective view of a part of the dosimeter according to FIG. 2.

Fig. 4 shows in parts another dosimeter according to the invention, and FIG. 5 shows a cross-section of the composite dosimeter according to FIG.

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The dosimeter collects a gaseous pollutant in proportion to its average concentration in the atmosphere during collection; 20 period and provides appropriate determination of this concentration. This is achieved by passively sampling the: gaseous contamination in the ambient air proportional to its concentration therein, in that the contamination can diffuse into an internal portion of the dosimeter, where it is retained by 15 | a collection medium placed therein until the contamination is analyzed.

The collection medium keeps the gaseous contamination or its!

ions solid in a form that is easier to analyze than! ! ; I

| the gaseous form. After collection, the medium is removed from the dosimeter and treated with a suitable reagent to generate a color, the intensity of which is dependent on the amount of igas contaminant collected. The time-averaged ambient concentration can then be determined, as will be explained below, with a pre-calibrated colorimeter or spectrophotometer. In a ! In another embodiment, the impurity can be separated from the collection medium and its amount determined, for example, according to the principle of gas chromatography, the results of the gas chromatographic analysis being pre-calibrated with respect to | to known time-averaged environmental concentrations of the 40 rein contamination. The preferred method of assay 81 028 92

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3 is done according to the colorimetric principle.

Generally, the collection medium is a material that absorbs :! bears, adsorbs, reacts or is otherwise combined j

j with the gaseous pollutant to be measured. Independent of the mode i i i 'I

: 5 i on which the medium interacts, as mentioned above, with the medium! : i! contamination, the amount or strength of the collection medium must be : are sufficient in the dosimeter to fully act on the total amount of gaseous pollutant expected to be collected. The collection medium will often be specific to the particular gaseous pollutant being monitored. Examples intended to be representative but not limiting include aqueous solutions of oxidizing agents or triethanolamine to absorb nitrogen dioxide, solutions of potassium or sodium tetra-1 chlorocurate to absorb sulfur dioxide, solutions of sulfur-15: acid or other acids to absorb ammonia and distilled water | or a solution of sodium bisulfite to absorb formaldehyde. Large-area charcoal or carbon powder, metal powders or metal salts can be used to adsorb many other organic contaminants.

i: 20 Methods for colorimetric analysis, for example, of sulfur dioxide, nitrogen dioxide, ammonia or formaldehyde in air are described in "National Institute for Occupational Safety and Health", methods No. 160 (publication 121, 1975), 108 (publication 136, 1974) ), 205 (publication 121, 1975) and 125 (publication number J; 25 136, 1974), respectively. The techniques described therein are readily adaptable with respect to the absorbent solution and color-forming reagents for the use in connection with dose collection. meter according to the invention.

A preferred embodiment of the invention 30 is shown in FIGS. 2 and 3 and may be constructed as follows. An base plate 3 of an impermeable polymeric material forms one side

Ivan the holder part of the dosimeter. The plate is preferably transparent and thermoplastic and can be made from polymers of;

olefins, halogenated polymers, polyesters, or ionomer resins. Bee ! I I

Preferred materials to use are the ionomer resins described in U.S. Patent 3,264,272 issued August 2, 1966 to iR.W. Rees. They are the ionic copolymers of α-olefins and a, β-ethylenically unsaturated carboxylic acids with 3-8 carbon atoms with 10-90% of the carboxylic acid groups neutralized with metal ions.

The size of the plate 3 is not critical, but is preferably

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81 028 92 4 a size that can be easily adapted to the application in a personal dosimeter that is to be worn or transported easily. The collection medium is placed in the central part of the plate 3. When the medium is a liquid, this can be accomplished by first forming an indentation in the center portion of the plate by applying pressure to it with a suitable mandrel using heat or otherwise. The pressed-in area of the plate 3 is the central part of the interior, indicated by 5, of the dosimeter.

After the collection medium has been applied to the plate 3, a second top plate 4 corresponding to the plate 3 in composition and size is placed over the plate 3. Heat and pressure are then applied to the three areas 6 to obtain a permanent fluid-tight connection at the three corresponding edges of the plates 3 and 4. Adhesives or other forms of compounds can also be used provided the compounds are permanent and fluid tight and the adhesive is inert to the collection medium.

An elongated gas diffusion device 1 provided with a number of 20 continuous channels 2 is not connected parallel to and near the fourth; the edge of the base plate 3 and arranged parallel to and in line with the fourth unconnected edge of the top plate 4. The open channels 2 of the device 1 are thus oriented horizontally with respect to the; plane of the plate 3 and perpendicular to the fourth edges of the plates 3 and 4. On the inside 7 of the device 1 a | i! ! | porous water-repellent film the channel openings of this inside, | which will be described in detail below. The diffuser 1, which is thus placed between plates 3 and 4, is connected to the plates by supplying heat and pressure or by using adhesives which must be impermeable and chemically inert to the collection medium 1.

The connection between the diffuser 1 and each of the plates 3 and 4 must be liquid-tight and airtight, so that the interior space of the container formed by the plates 3 and 4 is completely enclosed.

The relative placement of diffuser 1 and plates 7 and 8 is such that the channels 2 form the only connection between the atmosphere and the interior space 5 of the container.

It is also possible, when forming the dosimeter according to FIGS. 2 and 3, to store the collection medium, if it is a liquid, until the latter. In such a case

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81 028 92 5, the dosimeter is formed in a different manner. The collection medium j can be applied by piercing the top plate 4 in a j! i | appropriate point using a hypodermic needle and by injecting a measured amount of the collection medium into the interior 5: space. The hole formed by the injection needle can then be thermally sealed.

The diffuser 1 allows the gaseous pollutant to diffuse through each of the channels 2 according to Fick's law, which is expressed as follows:

10 M = D.C.t A / L

where, M = the amount of gaseous pollutant transferred (mg) D = diffusion coefficient of the gaseous pollutant by air (cm2 / min) C - concentration of the pollutant in the atmosphere (mg / cm3) t = exposure time (minutes) A s cross-sectional area of the channel (cm ^) 20; L = distance in diffuser, here channel length (cm).

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The values of D for various gaseous pollutants are; easy to find in the literature. The pure diffusion nature of the transfer of the gaseous pollutant through the channels at a rate linearly proportional to its atmospheric concentration | vert the integrative nature of the dosimeter.

The gas diffusion device 1 is preferably manufactured from materials. rials that are non-hygroscopic and are chemically and physically inert i; are for the gaseous pollutant and the collection medium.

Examples are polyethylene, polypropylene, polymers or copolymers of tetrafluoroethylene and hexafluoropropylene and stainless steel. The above-mentioned polymers are preferred since they can be easily manufactured by injection molding.

As shown by Fick's law, the number and diameter of the channels affect the amount of gaseous pollutant collected, as they affect the total cross-sectional area available for transfer. The amount of contaminant collected is also inversely proportional to the length of the channels. While these parameters are not necessarily critical to the integrating action of the diffuser, it has been found that 81 028 92 6 when each of the channels has a length to diameter ratio of 1. at least 3, preferably at least 4.5, the dosimeter obtains the desired insensitivity to relative atmospheric movement caused by wind or movement of the wearer. Furthermore, it has been found that the 5; use of about 5-500 channels, preferably 10-100 channels, each; with a diameter of about 50-1000 µm and a length of about 1.0-25.0 mm, preferably 3.0-8.0 mm, yields a device sufficiently sensitive to low pollution concentrations, but still an advantageous small in size.

10 A porous water-repellent film of 15-1000 µm thick is spread over the; channel openings are placed on the inside 7 of the diffuser 1, the side which communicates with the interior space 5 of the dosimeter. For example, the film can be made from polymers or copolymers of tetrafluoroethylene and hexafluoropropylene. The function of the film is to prevent the absorbent solution, when using that form of collection medium, from entering the channels | flows from the diffuser and further prevents sensitivity to atmospheric movement. Therefore, the porosity of the film and the size of its pores must be chosen such that these functions are performed without disturbing the flow of the gaseous contaminants from the interior ends of the channels to the absorbent solution. That is, the diffusion of the gaseous

contamination by this film must be significantly greater than the dif- ! I

| fusion through the channels, so that the total degree of diffusion is essentially j! ! 25 is controlled only by the channels. It has been found that a film that I I | 50-80% is porous with a pore size of 0.1-3.0 µm sufficient for this purpose when using the channels described above. ;

The diffuser 1 of FIG. 1 and the dosimeter according to the 30! Figures 2 and 3 are an example of preferred embodiments; Ring forms of the invention, however, the invention is not intended thereto. limited. For example, the diffuser may be in the form of a stopper sealed in the plane of either plate 3 or plate 4. Even! once the dosimeter holder need not be bag-shaped as described above, but may, for example, be in the form of a rigid cuvette.

Such an embodiment of the invention is shown in Figs. 4 and 5. In these figures, a personal dosimeter is shown, which consists of a circular base plate 8 with cylindrical walls which define an open cavity 9. The base plate 8 is provided with flanges 81 028 92 ♦ 7 13 with circular openings 14, whereby the composite dosimeter: i: can be easily attached to a person's clothing. A circular cap 11 grips in a frictional fit over the base tray 8, thereby forming a closure of the container 9.

The cap 11 has a plurality of channels 12 of circular cross section extending therethrough to the cavity 9. The ducted hood 11 functions as a gas diffuser according to Fick's law and therefore the number, length and diameter of the ducts 12 of the hood 11 are selected as described for the ducts 2 of the diffuser 1.

The cap 11 and the base tray 8 are preferably made of materials that are not hygroscopic and are both chemically and physically inert to the gaseous pollutant and the collection medium. The materials described for the construction of the diffusion device 1 are also preferred for the hood 11 and the base tray 8.

A porous water-repellent inert film 10 is placed over the channel openings on the inner surface of the cap 11. This film performs the same functions as described above with respect to the dose meter 20 of Figures 2 and 3. The film 10 is preferably 15-1000 µm thick and has a porosity of 50-80% with a pore size of 0.1-3.0 µm. It is preferably made from polymers or copolymers of tetrafluoroethylene or hexafluoropropylene, although any water-repellent inert material with the above physical properties is sufficient.

In assembled form, the frictional fit between base tray 8 and cap 11 is liquid-tight and airtight, so that the cavity 9 of the tray i! 8 is completely shut down. The channel 12 of the hood 11 forms the only connection between the atmosphere and the cavity 9 and the collection medium therein. The collection medium preferably completely fills the cavity 9 and is retained therein by the film 10 against seepage through the channels 12.

During operation, a dosimeter according to the invention is exposed to the air containing the gaseous pollutant for a period of time during which the average pollutant concentration! I! is being investigated. If the collection medium is an absorbent solution, then, for example, a measured amount of the solution is drawn out of the dosimeter by, for example, a syringe.

; ; i 40 j When the analysis is to be carried out photometrically, the

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81 028 92 8 *) I collected absorbent solution mixed with suitable color-forming reagents that change the color of the absorbent solution. The inten-! ! The identity of the color thus formed depends on the amount of gaseous pollutant collected. Although it is often desirable to provide a self-acting dosimeter, such as in the United States. This patent is shown, sometimes impractical, in patent 4,208,371, where the reagents are present in the dosimeter and no material collection is required. An example is an embodiment i in which the reagents are strongly acidic as in the color production for formaldehyde, wherein the reagents are chromotropic acid and sulfuric acid.

In such cases it is difficult to package the reagents in a stable and safe form and the simple dosimeter according to the invention is well suited for these applications.

The dosimeter according to the invention can be calibrated to obtain a direct relationship between colorimetric or spectrophotometric readings and the average ambient concentration of the gaseous pollutant. This can be accomplished by using a calibration procedure similar to that described in U.S. Patent No. 4,208,371. In such a procedure, several dosimeters are exposed for a certain period of time. various known concentrations of an impurity for which the calibration is intended. The dosimeters contain the same types and amounts of collection medium. For example, spectrophotometric readings are determined for at least two dosimeters at each of several known concentrations and a straight line is plotted! i i by the data points thus obtained using the least squares method. j

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Claims (8)

1. Personal dosimeter for collecting a gaseous! ! 1. contamination proportional to its average ambient concentration! during the collection time, characterized by a closed container; A: 5 | gaseous pollutant collection medium within the container; | a diffusion device which forms part of the boundary of the said container, which device is provided with a number of continuous channels through which the gaseous pollution can diffuse from the atmosphere into the interior space of the container, which channels each have a length to diameter ratio of at least 3 and said channels form the only connection between the atmosphere and the interior of the container; and a porous water-repellent inert film covering the openings of said channels on the inside. Dosimeter according to claim 1, characterized in that the container is a flexible bag made of a polymeric material. 3. Dosimeter according to claim 1, characterized in that the container in principle consists of a dish-shaped reservoir with an open end and a cap which grips the reservoir and covers the open end, the diffusion device being formed by at least one part of the i: I hood. Dosimeter according to claim 1, 2 or 3, characterized in that they are 5-500 channels each with a diameter of 50-1000 µm and a length of 1.0-25.0 mm. i Dosimeter according to claim 4, characterized in that the channel .......; length is 3.0-8.0 mm and there are 10-100 channels. Dosimeter according to claim 4, characterized in that the film has a thickness of 15-1000 µm, a porosity of 50-80% and a pore size of 0.1-3.0 µm. 130 Dosimeter according to claim 6, characterized in that the collection medium is an absorbent solution. Dosimeter according to claim 7, characterized in that the absorbent solution is for formaldehyde. i | ; i i 81 028 92