Expert Article Library
A New Standard Of Care In Absorbing And Dissipating Forces
By Dr. Carl J. Abraham, P.E. Email: CJAbraham1@aol.com
[Second of 2 Parts - Click for Part 1]
One of the proposed mechanisms for the enhancement and dissipation of forces is as follows: (1) the primary forces are received by the preform attached to the shell, (2) the shell then receives the secondary forces and dissipates them into the padding inside the shell, (3) the padding distributes the forces further and, (4) the remaining and extended dissipated forces are then distributed to the head and brain.
The thickness of the "preformed break-a-way" padding in the testing was Rubatex's 310-V (R 310V) and was 1/4 of an inch thick. The preformed padding is connected to the various designated parts of the outside of the shell by a system that can break-away. Velcro is one example. The use of the attachment has a two-fold purpose: (1) for attachment and, (2) to release if the glancing blow is greater than the force of the Velcro attachment. The latter sacrificial detachment is an additional benefit for the absorption and dissipation of forces. The padded sacrificial padding can be either replaced or put back where it came off.
The amount of energy absorption and dissipation of the forces depends on the thickness and type of pre-formed break-a-way padding applied. The end result is that the resultant forces to the head and brain are reduced significantly. This approach is directed to the reduction of the risk of injuries in both contact and non-contact sports that can be utilized in protective equipment such as shoulder pads as well as the boards surrounding an indoor arena.
The additional benefits of the proposed innovation invention are as follows:
- Minimal amount of weight is added to the helmet.
- No holes and metal attachments are added to the helmet for attachment of the preformed break-away padding.
- The preforms are placed in the most vulnerable areas where concussions occur on contact.
- The preforms will prevent and/or retard the cracking and failure of the shell in and around the ear.
- The preforms will not require any modifications or changes in the mold or design by the manufacturers.
- No additional padding will be required inside the shell.
- There will be no change in the size of the helmet.
- The preforms will be essentially the same size for all helmets in every contact sport and may vary in other helmets for use in such activities as biking and skiing.
- The enhancement will reduce the number of concussions to participants in all sports and extend the playing career of the participants.
- The benefits verses the cost to the user are overwhelming and in favor to both the manufacturer of the helmet as well as the user.
- Any damaged protective area is easily replaced without any tools in a matter of seconds with minimal cost.
- The colors of the pre-formed break-a-way padding can be made to blend in and match the colors of most of the protective helmets and/ or uniforms.
- Boards can be modified at any level (height).
- The preforms can be added to the vulnerable areas on the shoulder pads of the players.
- The resultant impacts to modified shoulder pads and modified helmets are significantly less, reducing the risk of injury as compared to systems which currently exist.
The tests results, proving the feasibility of significantly improving the energy attenuating system are shown in Figure 1 [not reproduced]. What this demonstrates is that without optimizing the energy absorbing system the risk of injuries can be reduced significantly for many products involving protective systems. This relatively simple and inexpensive system can be applied to helmets of all types, protective equipment such as shoulder pads and the upper part of the boards around the rink. The end result is that a higher standard of care could be obtained reducing the risk of injury.
United States Patent 6,272,692 titled "Apparatus For Enhancing Absorption And Dissipation Of Impact Forces For All Protective Headgear" was issued on August 14, 2001 that covered the method of protection described above.
The insert for the helmets and sneakers were prepared by creating a sandwich consisting of a 3/16-inch polyethylene film base, R 310V, 3/8-inch foam containing cylindrical steel springs 3/8 inch apart with varying K (stiffness) values. The top was covered with 1/4-inch R 310V foam.
Static compression tests were performed on a Nike sneaker in the heel area. This was also done with one of the hockey helmets. A one-half inch diameter probe was used to apply an increasing load to the subject material in the heel area. The sneakers were tested up to 250 pounds. The helmet bottomed out at a 100-pound load. The sneaker was made of compressible foam material with numerous strategically shaped and placed, embedded plastic air bladders. (See Figure 2 and 3; not reproduced).
The static testing did show that the feasibility of using a spring type mechanism in conjunction with a cushioning polymeric material shows some potential. The static testing indicates some correlation with the dynamic testing. At the lower loads, there was no evidence of the springs bottoming out.
The initial approaches taken by the author in the studies were as follows:
- Set a series of steel springs in a fixture and place them in critical areas of the product.
- The sandwich (insert) consisting of a 3/16-inch polyethylene film base, R 310V, 3/8-inch foam containing cylindrical steel springs 3/8 inch apart with varying K (stiffness) values. The top was covered with 1/4-inch R 310V foam.
- Series of steel springs, with K values of 10, 23, 45 and 75 lbs/in were fitted into 4" X 4" X 3/8" R-310V with 1/4 inch holes at 3/8 inch spacing.
- Substitute 3/8-in. R-310V in lieu of Nike's air pressured cushions.
The cushioning in the heel was removed and replaced with a 4" X 4" R-310V as described above in both hockey helmets and the sport shoes. The initial testing incorporated the use of a simple compression spring that is an open-coil helical spring that offers resistance to a compressive force applied axially. The compression spring was coiled with a constant-diameter cylinder. They were stress-relieved to remove residual forming stresses produced by the coiling operation. They were also designed and manufactured so that they could compressed without permanent set.
ASTM 1045 protocol was applied to the hockey helmets tested. The impact was made at the ear area. The head form was dropped at an average rate of 4.52 meters per second on a MEP pad with a Shore A60 hardness.. The results are shown in Figure 4 [not reproduced].
What is important to note is that:
- The springs and polymeric system can absorb and dissipate forces together enhancing the performance. This was documented by the fact that the depth of the indentation of the springs decreased from the center of the impact outwards.
- Cylindrical springs have limited usage and are not the proper design for protective sports products.
- If the cylindrical springs show some improvement in the feasibility study, the conical spring/foam system should absorb and dissipate significantly higher impact levels.
[space]The cylindrical steel springs bottomed out. This was not because of the K factor. They bottomed out due to the fact that there was not sufficient room for the system to travel. The only way to overcome this problem is to switch to conical springs. Unlike the cylindrical spring, the conical spring is a variable spring that gets stiffer at the end of the travel distance and will be able to easily handle the forces applied. References 39 and 40 describes the use and application of conical springs in conjunction with the polymeric cushioning.
Testing of the latest proposed system was not completed for the present study. Conical springs were made as well as prototypes for running shoes and helmets. A cursory preliminary evaluation allows one to easily predict that the alternating conical spring design will work because: (1) more springs per unit area can be used relative to the cylindrical springs, and (2) the more accommodating fit of alternating the conical springs and the polymer allows for significantly more interaction between the springs and the polymer. This design alone allows one to easily conclude that the problem presented can be solved.
For the first time in the application of polymeric materials used as energy absorbing materials, the feasibility of a method of enhancing the levels of performance has been demonstrated and tested. The system, as of this date, has not been optimized.
A new standard of care may be necessitated if it is foreseeable that there is technology available that will minimize and/or eliminate injuries that are occurring and, foreseeable will occur in the future. Consideration of a risk/utility analysis and cost must also be part of the analysis. The technology must be practical and not be cost prohibitive.
It is accepted that the present designs of hockey helmets has eliminated subdural hematomas in that contact sport. The current testing protocol followed by the CSA, ASTM and ISO are adequate and, in the opinion of the author, modification of the test methods involved along with the certification programs do not need any changes. However, the application of the unique energy absorbing systems described in this paper can change the levels of acceptance for certification.
The energy absorbing system incorporating the conical spring systems in conjunction with the polymeric cushioning materials can be extremely beneficial to the sport shoe markets. The time for recovery after each impact is instantaneous. In addition, the technology can be applied to all protective equipment in every sport such as helmets, shoulder pads, shin pads, elbow protection, crash mats, gym mats, wrestling mats, landing mats, as well as swimming pools, dasher boards and kick plates. The technology will not change the design of the present molds and, therefore, there will be minimal cost to each of the manufacturers to enhance their product lines.
Additional advantages are realized when there is a collision between, for example, the helmet of one player and the shoulder pads of another player. If both of the players were wearing the enhanced protective equipment, the dissipation of forces would be significantly less than the current systems resulting in a much lower probability and risk of head injury. Another example of where the risk of injury would be reduced is when there is impact between the shoulder of the hockey player and the boards.
A prima facie case for product defect can be established through proof of defect, safer alternative design, and risk-utility analysis. One can now establish and present evidence in impact injury cases that (1) the design involved did not produce sufficient protection during foreseeable uses, (2) a safer alternative design exists, and (3) the risk of harm presented by the design outweighed its utility. For example, there is no question that there would have been minimal or no injury to Dr. Epstein had his helmet incorporated the technology demonstrated in this feasibility study. It is more probable than not, and within scientific certainty, that the helmet would not have split and the forces it was exposed to would have been dissipated.
If a helmet manufacturer can document the fact that it has a superior system to the ones suggested in this paper through testing, then any injured party would have little recourse to bring an action against the manufacturer.
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[Click for Part 1]