Chemical exposure indication device

A chemical exposure indication device is disclosed. The device is removably attachable to a structure and includes a substrate having a first surface and a second surface and an indicating layer overlying the first substrate surface. The indicating layer includes a coating material that is chemically reactive with a pre-determined chemical compound that is known to degrade the structure. When the coating material is exposed to that corrosive compound in a pre-determined level associated with degradation of a metallic structure, the coating material provides a visual indication of the presence of the corrosive compound.

FIELD

The present invention relates to chemical detection and more particularly to devices for indicating chemical exposure.

BACKGROUND

In various industrial and military settings, the potential exists for exposure to corrosive or similarly hazardous chemicals. While analytical methods are available, they are unsatisfactory in many cases because they are expensive and time consuming and require trained personnel to operate and analyze the results. In many cases, other considerations mean that analytical methods are not an option even if cost were not an issue.

Prior non-analytical efforts to detect chemicals have been sought, but have focused primarily on the protection of humans using devices effective over a term typically measured in hours. Furthermore, levels of exposure that cause problems in materials are not necessarily the same as, and usually differ from, the types and levels of exposure that would pose danger to humans.

Non-analytical methods for protecting materials and equipment have largely been unsatisfactory, requiring significant amounts of time and expense associated with reactivation or stripping and re-coating after exposure. The processes of reactivation or stripping and recoating are hazardous, time consuming, expensive and may be incompatible with governmental environmental rules and regulations. Many coatings are also non-compatible with the structure to which they are applied, meaning that more expensive alternatives must be used, if available at all. Furthermore, in aircraft, the highest probability for chemical exposure of its exterior occurs when the aircraft is in flight, which is also the time when the exposure is most difficult to monitor through alternative techniques.

What is needed is a chemical indication exposure device that remains effective over long periods of time and which is capable of identifying harmful levels of chemical exposure for materials of construction, which often vary widely from harmful levels for humans.

SUMMARY

According to an exemplary embodiment of the invention, a chemical exposure indication device is disclosed. The device comprises a substrate having a first surface and a second surface, an indicating layer overlying the first substrate surface and means for removably attaching the device to a structure. The indicating layer comprises a coating material that is chemically reactive with a pre-determined chemical compound known to degrade the structure, such that when the coating material is exposed to a pre-determined level of the chemical compound, the coating material provides a visual indication of the compound's presence.

According to another exemplary embodiment of the invention, a chemical exposure indication device comprises a substrate having a first surface and a second surface, and means for attaching the substrate to a structure. The first substrate surface underlies an indicating layer of a coating material that is chemically reactive with a pre-determined corrosive chemical compound such that when exposed to a gaseous form of the chemical compound, the coating material changes color to provide a visual indication of the presence of the corrosive compound. The degree of color change is associated with the amount of corrosive compound to which the coating has been exposed. The device has an effective service period of at least one month in the absence of exposure to the pre-determined corrosive compound.

According to yet another embodiment, a chemical exposure indication device comprises a foil tape over-coated on one side with a layer of chemically reactive paint and having an adhesive on the other side. The paint changes color when the device is exposed to a pre-determined corrosive gas in a pre-determined amount that would cause degradation of a metallic structure to which the device is applied. The device has an effective service period of at least one month in the absence of exposure to the pre-determined corrosive gas.

One advantage of embodiments of the invention is that exposure to chemicals in amounts that cause degradation of metallic or polymeric structures can be detected.

Another advantage of an embodiment of the invention is that the exposure can be measured over long periods of time to measure cumulative exposure to corrosive chemicals.

Yet another advantage of embodiments of the invention is that when the device needs to be replaced, that can be accomplished quickly and easily without using environmentally unfriendly materials.

Still another advantage of an embodiment of the invention is that exposure to multiple different chemical compounds can be detected at the same time.

Where like parts appear in more than one drawing, it has been attempted to use like reference numerals for clarity.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the invention are directed to chemical exposure indication devices that provide a visual indication when the device has been exposed to a pre-determined level of a corrosive chemical compound.

Turning toFIG. 1, a side view of a chemical exposure indication device10is shown. The device10includes a substrate15having a first surface17and a second surface19. An indicating layer20overlies the first surface17of the substrate15.

The indicating layer20may be a coating of any material that chemically reacts when exposed to a pre-determined chemical compound to provide a visual indication that the exposure has occurred. In one embodiment, the indicating layer20changes from a first color to a second color in the presence of a pre-determined chemical compound. The coating is generally selected to be responsive to a particular chemical compound which degrades a metallic or polymeric structure, such that the color change occurs when the level of exposure reaches a pre-determined level that may be any level greater than zero. By “degrades” is meant that the chemical compound is corrosive to the structure or that the chemical compound accelerates environmentally assisted cracking of the structure, either of which can lead to premature failure of the structure.

Preferably, the pre-determined level of exposure is a level that is associated with degradation of a particular metallic structure of interest. In one embodiment, the color change occurs gradually, such that the cumulative effects of any level of exposure to the chemical compound of interest can qualitatively or quantitatively be assessed over time. As a result, if some exposure has occurred, it can quickly be determined whether the exposure levels warrant additional inspection.

The substrate15may be any metallic, ceramic, polymeric, natural or manufactured textile material or film that is compatible with the environment in which the device10will be used. The substrate15should also be compatible with the material(s) with which the substrate15will be coated. In one embodiment, the substrate15is aircraft speed tape or some other form of adhesive foil tape.

Chemical compounds which are particularly harmful to metallic or polymeric structures and which are of interest for detection include chlorine, iodine, ammonia, hydrogen peroxide, alcohols, such as methyl alcohol, and alkaline hydroxides (e.g., sodium hydroxide and potassium hydroxide). It will be appreciated that in most cases, the levels at which these compounds are harmful to structural materials are not the same as those in which the levels are harmful to humans. For example, humans are able to consistently be exposed to ammonia at levels of up to 1000 ppm, while as little as 5 to 20 ppm can have significant long term effects on metallic structures. As a result, the particular material for the indicating layer20is selected for both the chemical compound of interest and the level of exposure of interest for the particular structure. The material for the indicating layer20is also preferably responsive to the particular compound of interest in its gaseous and vapor (e.g. aerosol) forms.

In one embodiment, the indicating layer20is a color changing paint. Exemplary paints include paints that incorporate pH indicator or goldenrod dye. Another exemplary color changing paint is available under the trademark ON GUARD from AWC, II, Inc. of Smithville, Mo. After the color changing paint applied to the substrate15dries, the paint provides a dry chemistry for the indicating layer20. This results in a device10that is effective for a month, six months, a year, or longer, unless spent earlier due to maximum exposure, at which point it would be replaced. That is, even after long service periods without exposure to the pre-determined compound with which the indicating layer20is associated, the device10will suffer no adverse effects and still function properly even if the first exposure to the particular compound does not occur until well after the device10is put in use. Sol-gels may also be used for the indicating layer20, but due to their wet chemistry characteristics, an indicating layer20of a sol-gel material may become less effective more quickly and thus require more frequent replacement of the device10.

The device10further includes a means for attaching the device10to a structure. The means for attaching the device10may be the substrate's second surface19, or it may be a separate layer or device. For example, in one embodiment the substrate's second surface19may be magnetic, may have a static charge, or may be tacky, any of which could permit direct adherence of the second surface19to a structure. In another embodiment, as illustrated inFIG. 2, an additional adherent layer40may be added to impart the ability to attach the device10to a structure. The adherent layer40may be a separately applied layer of adhesive, double-stick tape, or a separate magnetic base, for example. Other suitable means for attaching the device10to a structure include mechanical fasteners, such as rivets, bolts, weldments, clamps, clips, a card frame or any combination of these.

As illustrated inFIG. 2, a removable backing layer50may be applied over the adherent layer40or directly to the substrate15to provide a “peel and stick” type device10which may be particularly useful where the device10is to be attached by an adhesive or through static cling. The backing layer50can be used to prevent premature adherence of the device10to something other than the desired location on the desired structure. As also illustrated inFIG. 2, a primer layer30may be used intermediate the substrate15and the indicating layer20to promote adhesion of the two layers. A removable protective layer60may also be provided over the indicating layer20so that the indicating layer20can be exposed to the environment at a desired point in time, such as after the device is attached to the desired structure.

Turning toFIG. 3, a top view of a chemical exposure indication device10is shown attached to a structure100. Generally the structure100to which the device10is applied is at least partially constructed of the particular material for which exposure to one or more particular chemicals is desired to be monitored. However, the device10may be applied to a structure100that is in the same general location as the material to be monitored. In one embodiment, the structure100is an aircraft in which one or more devices10are placed at various locations on the exterior and interior of the aircraft. Particularly with respect to placement on exterior locations of an aircraft, the locations may be selected such that the devices10can be viewed using cameras so that in-flight monitoring of chemical exposure can be accomplished.

However, the structure100may be any structure that is constructed of, or is in the same environment as, a material for which exposure to particular chemical compounds is desired to be monitored. For example, the device may be used on a structure wherever it is desirable to detect chemical leakage, chemical jettison, chemical impingement, or chemical entrainment, by way of example only, that could damage the structure100or other equipment or materials in the vicinity of the structure100to which the device10is applied. Exemplary structures100include, without limitation, vehicles, aircraft, storage drums, and pipelines.

As illustrated inFIG. 4, multiple different indicating layers20,22,24,26,28may be applied to the same substrate15. Each indicating layer is associated with a different chemical compound, such that a single device10may be attached to a structure100for use in simultaneously detecting whether exposure has occurred to any one of several different chemical compounds.

FIG. 5illustrates another embodiment in which one or more indicating layers22may be applied in the form of indicia, such that when the indicating layer22is exposed to the corresponding chemical compound, the indicia becomes apparent. As a result, when a particular indicating layer is exposed to its corresponding pre-determined chemical compound, only the letters or other form of indicia changes color. The indicia may be letters which spell out the name of the compound, a chemical formula, a chemical structure, or other any other pre-determined symbol that is selected to be associated with the particular chemical compound to which the indicating layer22corresponds.

To achieve the indicia, the indicating layer22is applied over only a portion of the substrate15or primer layer30. The indicating layer22may be applied as the desired indicia, for example using a stencil, or alternatively, the indicating layer may be applied as the background (i.e. a reverse stencil), leaving the primer layer30or substrate15as the indicia. In either case, the indicating layer22results to form the indicia when the color change occurs. The substrate15or the primer layer30should be selected to match the pre-exposure color of the indicating layer. As a result, prior to exposure, the indicia cannot be seen, but when the indicating layer changes color, it is contrasted against the background of the primer layer30or substrate15that allows the indicia to easily be seen and easily identify the particular compound for which exposure has occurred.

Providing an indicating layer that results in the appearance of indicia upon exposure may be particularly useful when the exposure device10is used on the exterior of an aircraft or in other situations in which the device10is to be monitored via a closed-circuit camera. Closed circuit cameras are often black and white and vibration of a moving aircraft can make focusing on or resolving an overall color change challenging, but which is aided by the contrast of the indicia against the background. Applying the indicating layer22to form indicia may also avoid the need to identify or remember the order in which the indicating layers were applied before being able to subsequently determine to which chemical(s) the structure was exposed. The indicia is also useful in the event that the device10is inadvertently applied upside down, and thus may help to prevent misidentification of exposure to a particular chemical.

The means for attaching the device10to the substrate100is selected such that exemplary embodiments are readily removable from the structure100to which they are applied. That is, while the device10is adequately secured to the structure100so that it doesn't unintentionally come off even when attached to the exterior of an aircraft in flight, it can readily be removed for replacement after exposure or routine maintenance without the need to re-activate the indicating layer in place on the structure100and without wide-scale stripping and re-application. The device10can then be disposed of in an environmentally safe way. Alternatively, if re-activation is a possibility, it can be accomplished safely in a laboratory environment. Furthermore, potential damage to the structure100during stripping or re-activation operations is minimized.

While two or more indicating layers20,22may be used on the same substrate15, the use of multiple separate devices10each having a single indicating layer20, each selected to indicate exposure to a different chemical compound, allows the devices10to be spaced apart from one another on the structure100. This may decrease or avoid problems which can occur due to incompatibility between indicating layers20of different materials or other interference that can result in false indications. Additionally, because the indicating layer(s)20are applied to a substrate15, and not directly to the structure100, compatibility problems between the indicating layer20and the structure100are also avoided.

Exemplary embodiments provide a quick way to detect unsafe levels, or any levels depending on the material selected for a particular indicating layer, of a particular chemical compound without expensive, cumbersome and time consuming analytical testing devices and equipment and can therefore be accomplished by untrained personnel. Thus, embodiments of the current invention may find use in military applications, as well as in commodity and specialty chemical industries, the pulp and paper industry, mining and refining industries, petroleum and petrochemical industries, fuel handling and delivery industries, transportation industries, food packaging and processing, refrigeration manufacturing, packaging, installation and monitoring and municipal applications, by way of example only.