Patent Application
20050247310
1. Filed of the Invention
The invention provides for a novel chemical/biological protection enhancement system that is relatively inexpensive, lightweight, and could be tailored for civilian and military chemical/biological applications. No chemical/biological masks currently exist that use this process for protection enhancement. The invention uses a novel system that provides for very high levels of protection in known chemical/biological environments without the use of a self-contained breathing apparatus.
2. Brief Description of Related Art
Military and commercial chemical/biological masks fall into three general categories: negative pressure, positive pressure, and self-contained. Negative pressure masks utilize one or more filtration systems to process external filtered air into the wearer's respiratory air stream. Positive pressure units circulate external filtered air into the wearer's air stream using a fan or blower to pressurize the mask and minimize the leakage potential caused by negative pressure in the mask. Self-contained systems utilize an air source to supply or recycle air using an internal or enclosed process to shield the wearer from the environment. These are ideal for very high concentration chemical/biological environments or for environments where the elements are completely unknown. Many self-contained systems provide a level of positive pressure as well.
Negative pressure masks have limited protection capabilities. Protection factor results can range from little to no protection to 100,000:1 on a fully sealed mask. Even on a good sealing mask, leaks can be generated through facial movements, foreign matter in the seals, or through higher breathing rates. Table 1 is an example of a good sealing mask on a static head form. Protection factors are quite high at reduced breathing rates but decrease as the breathing rate increases.
Positive pressure masks offer the potential for increased protection factors. Protection factors can range from several thousand to well over 100,000:1 on a fully sealed mask. Tables 2-4 demonstrate the potential for increased protection factor using a variety of blower flow rates. Increasing the airflow into the mask will generally increase the protection factor of the mask. However, these protection factors are still influenced by breathing rates of the individual. Tables 2-4 demonstrate how increased breathing rates can significantly reduce the performance of a positive pressure system even on a fully sealed mask. When a user breathes faster due to higher work rates, the user can exceed the flow rate of the blower causing a negative pressure in the mask and additional seal leakage. This causes a negative pressure in the mask which brings air in from the outside.
Self-contained systems can provide very high protection factors well over 100,000:1. These systems are ideal for environments where the chemical/biological concentration is extremely high or where the hazard is completely unknown. Unfortunately, these systems are very limited in capacity. Wear times can range from several minutes to several hours. They are also very heavy and bulky, frequently requiring hoses and tanks. System weights can range from several pounds to 40 or 50 pounds depending on the system capacity.
Therefore, there is a need for a chemical/biological protection system that provides enhanced chemical/biological protection over conventional negative and positive pressure systems but is not as bulky as a self-contained system. There is also a need to provide a chemical/biological protection system that is still effective when a wearer's breathing rate increases.
Therefore, an object of the present invention is to provide a system that gives enhanced chemical/biological protection over conventional systems.
Another object of the invention is to provide a system that is not as bulky as a self-contained system but is more efficient that a negative pressure or positive pressure system.
Another object of the invention is to provide a system that compensates for increased breathing rates without sacrificing chemical or biological protection to the user.
These and other objects are met with the present invention that provides an improved protection factor that is independent of the wearer's breathing rate. The invention is a viable improvement over negative and positive pressure systems and offers a more stable protection level and can be easily adapted to almost any mask system.
The present invention solves the problems of the past chemical/biological protection systems by providing an enhanced protection to a user by adding a separate filter-blower system to a chemical/biological hood. The filter-blower system provides overpressure to the hood system only. This makes the overpressure independent of the wearer's respiration so that over-breathing of the positive pressure is not possible.
The invention utilizes a separate filter-blower system that is part of a chemical/biological hood. This chemical/biological hood provides overpressure to a chemical/biological mask system. The overpressure created is independent of the wearer's respiration so that over-breathing which pulls outside air into a chemical/biological mask is not possible as the hood remains under a positive pressure.
The filter-blower hood system of the invention is a chemical/biological hood capable of providing enhanced protection when it is integrated with a chemical/biological mask. Cinching or sealing of the secondary hood at the neck improves overpressure performance.
In one embodiment of the invention as shown in
The hood is made of a chemical/biological resistant material.
The filter-blower system 2 that is used with the invention would typically be lightweight and head mounted. This would eliminate the need for external hose and wire systems that are commonly worn on the body. The filter blower 2 would preferably be mounted in the back of the hood but could be mounted any other location that was convenient and comfortable. The filter-blower system would preferably provide up to 2 cubic feet per minute of clean air into the hood on a continuous basis.
A schematic representation of the filter structure is provided in
The filter is typically designed to provide a pressure drop in the range of 1″ of H2O at a flow rate of 85 liters per minute. This allows the use of a small blower system suitable for head mounting. Typical surface areas for the filter are about 150-300 cm2. The filters typically incorporate a carbon loaded web media for vapor filtration and an electrostatic media for particulate filtration but could utilize any low resistance, chemical/biological filtration media.
A typical blower is similar to Micronel Safety C301® which is small and lightweight and can provide the necessary flows to accommodate the filter head pressure.
The sorbent layers of this invention typically are made from a carbon-loaded web 6 shown in
The particulate layers 7 shown in
Edge sealing is accomplished either with a silicone adhesive sealant or a thermoplastic edge seal adhesive. Compressing stacked media in a mold and injecting edge seal material in a cavity around the stacked media creates edge seals. Edge seal sizes are about 0.25″. An example of a sealant is BJB F60 polyurethane. This material offers fast curing cycles at low temperatures. Temperatures no greater than 150 degrees F. are required to prevent media degradation during the edge sealing operation.
Compress stacked media can be used as a filter. Stacking media in this fashion allows for the development of a low profile, thin bed filter that is more difficult to achieve with traditional packed bed technology.
The filter is edge sealed using a polyurethane sealant similar to the BJB sealant described above. This is continuous for any embodiment. The filter blower is bonded or clamped into the hood and the hood is fitted or secured to the mask. No sealing is required of the filter blower to the hood.
To further demonstrate the advantage of the invention, Tables 5 and 6 show fit factor results using this concept on a partially sealing mask. Table 5 shows results with a relatively loose fitting hood. Fit factors increase slightly but remain fairly stable under all test conditions. Table 6 demonstrates the performance with a tighter fitting hood in which the hood is cinched around the neck. In this case, protection factor results improve significantly for each test condition. As an alternate concept, exhaled air can be used to supplement the pressurization effect. Tables 7 and 8 demonstrate these results under similar test conditions. In this case, improvements are apparent under both loose and cinched hood conditions.
Fit Factor is a ratio of the outside concentration over the inside concentration. For example if the concentration of the external contaminant was 10 and the amount of contaminant sampled in the mask was 1. The fit factor would be 10:1.
It is preferred to use a hood with a draw string around the neck. A loose fitting hood in this example is a hood in which the draw string is not used. A cinched hood is one where the hood draw string is tightened.
Air is usually exhaled into the outside environment from a mask. The term purged hood means covering the exhalation valve and blowing exhaled air into the hood.
To better demonstrate the performance advantages of the invention, a leak was imposed in the mask seal. This highlights the advantage of the invention when compared to a traditional positive pressure system, which is dependent on the wearer's breathing pattern. Tables 9 and 10 demonstrate protection factor results with both loose and tighter (i.e. cinched) fitting hood conditions. These results demonstrate an ability to overcome a fairly large leak in the mask seal with a relatively small amount of overpressure. In the cinched hood condition, less airflow is generally needed to overcome the seal leak. Tables 11 and 12 demonstrate the same test conditions on an alternate configuration where exhaled air is used to supplement the purging effect. Although protection results tended to be lower, similar trends were observed.
Purging effect is the additional contribution caused by blowing exhaled air into the hood.
To further demonstrate the advantages of this invention, one additional test was performed. A traditional positive pressure approach in which the blower is placed in the wearer's respiration cycle was tested using a mask with a similar leak in the seal. Table 13 demonstrates these results at a breathing rate of 50 liters/minute. In general, the results indicate a limited ability to overcome the leak. Higher breathing rates would further reduce fit factor performance.
In comparison, Table 14 demonstrates the same conditions when using the filter blower hood as described in this invention. Fit factors are much higher since they are not affected by the wearer's breathing. Fit factors would also be more stable regardless of the breathing rate used to perform the test.
In conclusion, the invention demonstrates an increased ability to stabilize protection using an improved positive pressure device. This arrangement is much more independent of wearer breathing cycles and has the ability to overcome many leaks that might be imposed from facial movement or foreign matter. As a result, the invention offers a means to extend the performance envelope of a negative or positive pressure mask. This could lead to use in operational performance scenarios otherwise only considered for self-contained systems.
The invention described herein may be manufactured, used and licensed by or for the U.S. Government.
