Patent Application
20080011545
The present disclosure concerns an improved fall-arrest harness that reduces the risk of suspension trauma, a potentially fatal form of orthostatic intolerance. Orthostatic intolerance refers to the development of symptoms such as light-headedness, palpitations, tremulousness, poor concentration, fatigue, nausea, dizziness, headache, sweating, weakness, and occasionally fainting while the body is in a vertical position, particularly for long periods of time. For instance, when a person stands motionless, blood can accumulate in the leg veins (e.g., venous pooling) and cause orthostatic intolerance. Orthostatic intolerance also can occur when an individual moves suddenly after being sedentary for a long time, for instance when standing up quickly after sitting still for a long period of time.
Venous pooling typically occurs in the legs due to the force of gravity and a lack of movement. Blood normally is moved back from the leg veins to the heart through one-way valves using the normal muscular action associated with limb movement. However, if the legs are immobile, then these “muscle pumps” may not operate effectively, and venous pooling can occur. Since veins are expandable, a large volume of blood may accumulate in the veins.
Venous pooling reduces the amount of blood in circulation. The body reacts to this reduction by increasing the heart rate in an attempt to maintain sufficient blood flow to the brain. However, if the blood supply is significantly reduced, this increase in heart rate is not effective at maintaining adequate brain perfusion. During severe venous pooling, the reduction in blood flowing to the brain causes fainting and can have a deleterious effect on other vital organs, such as the kidneys. The kidneys are very sensitive to blood oxygen, and renal failure can occur with excessive venous pooling. If these conditions continue, they can be fatal.
When orthostatic intolerance occurs in a person who is standing (for instance, a soldier standing at attention for a long period of time), the individual can lose consciousness and collapse into a horizontal position. With the legs, heart, and brain on the same level, blood is once again returned to the heart. Assuming no injuries are caused during the collapse, the individual can quickly regain consciousness, and recovery is likely to be rapid.
A much more serious situation occurs in the case of suspension trauma, for instance in the case of individuals using fall-arrest systems. Following a fall, a safety harness user may remain suspended in the harness in a vertical or near-vertical position. The resulting sustained immobility in this position can lead to a state of unconsciousness. Depending on the length of time the suspended person is unconscious and/or immobile and the level of venous pooling, the resulting orthostatic intolerance will sometimes lead to death. Such injuries and fatalities are referred to as “harness-induced pathology” or “suspension trauma.” Symptoms of suspension trauma include faintness, nausea, shortness of breath, dizziness, sweating, unusually low or high heart rate, paleness, unusually low blood pressure, hot flashes, and loss of vision or visual disturbances. Factors that can affect the degree of risk of suspension trauma include the inability to move the legs, hypothermia, pain, shock, injuries sustained during the initial fall, pre-existing cardiovascular disease, fatigue, respiratory disease, dehydration, and blood loss.
Users of conventional fall-arrest harnesses who are unconscious or immobile while suspended in their harness are not able to move their legs and will not fall into a horizontal position, as they would if they fainted while standing. Suspension trauma is particularly likely to result if the suspended individual is left in place for some time. In addition, venous pooling and orthostatic intolerance can be exacerbated by other circumstances related to the fall. For example, shock or the experience of the event that caused the fall, other injuries, the fit or positioning of the harness, the environmental conditions, and the individual's psychological state all can hasten the onset and increase the severity of the condition. Unless the suspended individual is rescued promptly using safe procedures, venous pooling and orthostatic intolerance can result in serious or fatal injury, as the brain, kidneys, and other organs are deprived of oxygen. Suspension in a fall-arrest device can result in unconsciousness and death in less than 30 minutes.
The present disclosure concerns a fall-arrest apparatus for reducing the risk of suspension trauma to a user suspended from an elevated structure by a lanyard. As shown in
The body harness 10 can be of a conventional construction such as shown in
As shown in
As shown in
Although a particular exemplary harness is shown in
Specific, non-limiting examples of body harnesses that can be used with the fall-arrest apparatus disclosed herein include the Guardian Premium Edge Harness, Seraph Harness, Construction TUX Harness, Standard HUV Harness, Front-Loop Crossover Harness, Lineman's Harness, Kevlar Harness, Jacket TUX Harness, and the Sport Harness, all manufactured by Guardian Fall Protection, Kent, Wash.; The Miller Revolution Harness, Duraflex Ultra Harness, Duraflex Stretchable Harness, Duraflex Python Ultra Harness, Duraflex Python Harness, HP Harness, ProCraft Harness, Concrete Harness, Construction Harness, Oil Rig Harness, Tower Climbing Harness, Ms. Miller Harness, Warehouse Harness, Titan T4007, Titan T4500, Titan T4507, Titan T4078, Titan T4577, and the Utility Harness, all manufactured by Bacou-Dalloz, Smithfield, R.I.; the DBI Sala and the Protecta, both manufactured by Capital Safety, Red Wing, Minn.; the FallTech 7006P, FallTech 7015, FallTech 7590A, and the FallTech 7595A, all manufactured by FallTech, Inc., South Gate, Calif.; the Gravity Crossover Fall Arrest Harness, Classic Light Weight Harness, FP Classic Quick Fit Harness, FP Pro Harness, Confined Space Fall Arrest Harness, and the Gravity Tower/Rescue Harness, all manufactured by MSA PTY. Limited, Wentworthville, Australia, and the MSA TechnaCurv™ Tower Harness (Pittsburgh, Pa.).
As shown in
The leg loop 16 also can include a connecting strap attachment element, or ring, 56, which can be a generally ring-shape structure having an aperture for connecting a connecting strap 18 and a slot through which the strap portion 57 extends so as to mount the attachment element 57 to the leg loop. Padding 58 can be provided on the inner surface portion of the inner strap 50 of the leg loop 16. In some embodiments the padding 58 lines the full inner surface of the leg loop 16, wherein in other embodiments the padding 58 lines an inner surface portion of the inner strap 50 of the leg loop at a position that is opposite the connecting strap attachment element 56 (as shown in
The leg loop 16 also can include a connecting strap attachment element, or ring, 56, which can be a generally ring-shape structure having an aperture for connecting a connecting strap 18 and a slot through which the strap portion 57 extends so as to mount the attachment element 57 to the leg loop. Padding 58 can be provided on the inner surface portion of the inner strap 50 of the leg loop 16. In some embodiments the padding 58 lines the full inner surface of the leg loop 16, wherein in other embodiments the padding 58 lines an inner surface portion of the inner strap 50 of the leg loop at a position that is opposite the connecting strap attachment element 56 (as shown in
In this alternate embodiment, the leg loop 16 also can include a connecting strap attachment element, or ring, 56, which can be a generally ring-shape structure having an aperture for connecting a connecting strap 18 (
As shown in
The leg loop 16 can be constructed from any sturdy material, including fabric, leather, rope, cable, or webbing, or a combination for materials. One specific, non-limiting example of a suitable material is 3-inch wide nylon webbing with a tensile strength of at least 5000 pounds.
As shown in
In an alternative embodiment, a single connecting strap can be used in place of two connecting straps 18. In this alternative embodiment, the single connecting strap has fasteners at its opposite ends, each of which can be connected to a leg loop 16. An additional fastener that can be used to connect the strap to the lanyard 31 is secured to the strap at an intermediate location between the strap ends.
In another alternative embodiment, a single connecting strap 18 can be used that has a first end portion 60 that can be connected to the lanyard 31 and a second end portion 62 that can be connected to two leg loops 16. In this alternative embodiment, each leg loop 16 is connected to the second end portion 62 of the connecting strap 18 via fasteners 68 such that the distance between the two leg loops 16 is sufficient to permit freedom of movement for the user (e.g., allow the user to walk, kneel, and/or perform other intended tasks).
The connecting straps 18 can be constructed from any sturdy material, including fabric, leather, rope, cable, or webbing, or a combination for materials. One specific, non-limiting example of a suitable material is 2-inch wide nylon webbing with a tensile strength of at least 5000 pounds.
In use, as shown in
As shown in
Optionally, the portions of the upper body straps 20 between the lanyard and the user can be adjustable in length, for example, from about 24 to about 46 inches, or in more particular examples, from about 30 to about 40 inches from the end of the lanyard 31 to the user. For example, the portions of the upper body straps 20 between the end of the lanyard 31 and the user can be made adjustable by providing a plurality of apertures 78 spaced along the length of the first end portions 72 of the straps 20. The apertures 78 can be reinforced with grommets 80. The grommets 80 can be made of metal, and in particular examples they have an inner diameter of about one-half inch. In use, the straps 20 can be connected to the lanyard 31 by placing the connecter 71 through any of the apertures 78 to set the length of the strap portions extending between the lanyard 31 and the user.
As shown in
In alternative embodiments, the upper body strap assembly 18 can take the form of a single strap, rather than two straps connected to each other. In this alternative embodiment, the strap can have a releasable connector (e.g., a carabiner) secured at an intermediate location between the ends of the strap. The strap can be inserted through the shoulder rings 34 and connect to the lanyard 31 at its opposite end portions.
Alternatively, the upper body strap assembly can take the form of two individual straps that are not connected to each other. Each strap has a first end adapted to be connected to the body harness 10 at either the front lanyard attachment element 30 or the back lanyard attachment element 36 and a second end adapted to be connected at the lanyard.
In use, the upper body strap assembly 14 can be secured to the harness 10 at the harness attachment element 82 (
In other examples, the upper body strap assembly 14 can be attached to the harness 10 at the front lanyard attachment element 30 (
The fall arrest apparatus can be used by a user working on an elevated structure, such as a roof, scaffolding, crane, bridge, or other elevated structure. Desirably, the effective length of the upper body strap assembly 14 between the lanyard 31 and the upper body of the user is adjusted to permit freedom of movement for the user, while also being of sufficient length relative to the effective length of the lower body strap assembly 12 between the lanyard 31 and the leg loops 16 such that the legs are elevated to at least hip level as shown in
It will be apparent that the precise details of the apparatus described can be varied or modified without departing from the spirit of the described invention. The following example is provided to illustrate certain particular features and/or embodiments. This example should not be construed to limit the invention to the particular features or embodiments described.
This example illustrates the efficacy of a particular improved fall-arrest apparatus in preventing suspension trauma as compared to conventional safety harnesses.
Sample size calculations (two-sided T-test) were used to determine that a sample of 34 subjects was adequate to detect a difference of six minutes in suspension time or 10 mmHg in mean arterial pressure (MAP) with a power of 0.80 (α=0.05). The subjects included twenty-two men and eighteen women weighing less than 300 pounds and ranging in age from 18 to 45 years old. All men (age 34±8 years, weight 80.1±14.1 kg, and height 178.0 m±7.5 cm, values are mean±SD) and 14 women (age 34±9 years, weight 66.7±14.1 kg, and height 163.4±4.5 cm, values are mean±SD) had previous or current construction experience. Institutional review board approval, including informed consent, was obtained prior to any human subject testing. The MSA TechnaCurv™ Tower Harness (Pittsburgh, Pa.) with a pullover design was used for suspension tests. The harness had padding on the shoulder and leg straps and a padded waist belt. Harness fit was evaluated based on the location of shoulder straps, chest D-ring, hip rings, and back D-ring (according to the harness manufacturer's instructions). Fit was evaluated with the subject standing, prior to suspension and prior to the addition of the suspension trauma-preventing fall-arrest apparatus (e.g., the upper body and lower body strap assemblies, also referred to as the “harness accessory”). If the chest D-ring was between two and four inches above or below the center of the sternum, or if the back D-ring was between two and four inches above or below the mid-point between the shoulder blades, the fit was determined to be “fair.” D-ring locations less than two inches from their respective landmarks were deemed to be “good,” and D-ring locations greater than four inches above or below their landmarks were deemed “poor.”
Subjects were randomly assigned chest D-ring (“CHEST”) or back D-ring (“BACK”) attachment points. Suspension trauma-preventing fall-arrest apparatus (e.g., harness accessory, or “ACCESS”) tests were conducted during a four-week period after completion of all CHEST and BACK tests using 26 of the original subjects. For CHEST and BACK suspension tests, measurement of suspension time commenced after standing subjects were raised two inches from the floor. Subjects were raised from a seated position during the ACCESS tests.
The suspension trauma-preventing fall-arrest apparatus used in these tests was designed to deploy passively, in order to be effective when a suspended worker is seriously injured or unconscious. All subjects were asked to remain motionless for as long as they could during suspension tests. They were instructed that they could terminate the suspension at any time without penalty or loss of further participation in the study. Heart rate (HR), electrocardiogram (ECG), and pulse oximetry were continuously measured, and blood pressure (BP) was measured automatically every two minutes at heart level by a Dinamap Pro 1000V3 monitor (GE, Milwaukee, Wis.). Blood pressure was also measured during the last minute of suspension. Minute ventilation was continuously measured by a VivoMetrics LifeShirt (Ventura, Calif.) throughout the suspension period.
The suspension was terminated if suspension duration reached 60 minutes. Medical test termination criteria included the following signs of orthostatic intolerance: 1) a systolic blood pressure decrease of more than 20 mmHg as compared to the pretest value, 2) a diastolic blood pressure decrease of more than 10 mmHg as compared to the pretest value, 3) a heart rate increase of more than 28 beats per minute over pretest value, 4) a heart rate decrease of more than 10 beats per minute from baseline, or 5) a pulse pressure decrease to less than 18 mmHg (Streeten: Orthostatic Disorders of the Circulation. New York: Plenum, 1987). In addition, tests were medically terminated if any of the following signs or symptoms were reported or observed: shortness of breath, nausea, dizziness, or diastolic blood pressure >100 mmHg. Tests terminated due to extreme subject discomfort were reported as voluntary terminations.
The mean changes in physiological variables were analyzed for the effects of gender, body weight, and attachment point using a mixed model repeated measures analysis of variance (SAS institute, Cary, N.C.) on the combined medically- and voluntarily-terminated (“M+V”) CHEST and BACK test data. Suspension durations for the CHEST and BACK tests were analyzed using a Kaplan-Meier survival analysis, and the effects of gender, height and body weight on suspension duration were determined using a Cox regression model (R: A language and environment for statistical computing, Vienna, Austria).
Four men and two women completed only one, not both of the CHEST and BACK suspensions. The 15 men and 11 women who returned for the tests using the suspension trauma-preventing fall-arrest apparatus had subject characteristics identical to the original group of subjects.
The mixed model analysis of variance applied to the M+V data revealed no differences due to gender in any physiological variables, including pretest-to-test-termination changes in thigh circumference, minute ventilation, heart rate, and mean arterial pressure (MAP). Analysis of variance did demonstrate a significant relationship between body weight and change in MAP: during BACK suspensions. The pretest-to-test-termination change in MAP decreased as body weight increased (p≦0.05) for M+V. In addition, decreases in MAP were significantly greater (p≦0.05) with the BACK attachment point than CHEST for M+V. Table III shows separate mean changes in physiological variables for medically- and voluntarily-terminated tests. Changes were generally greater during medically-terminated tests than during voluntary or ACCESS tests.
Table IV and
The arithmetic mean for the ACCESS condition (e.g., the suspension trauma-reducing apparatus) was 58 minutes, median was >60 minutes (medical symptoms, if they occur, would occur sometime after 60 minutes), and range was 39-60 minutes (Table IV). There were no terminations due to medical symptoms, changes in physiological variables were small, and 85% of ACCESS subjects completed 60-minutes suspensions.
Most prior suspension tolerance research was conducted on young, healthy members of the military service (Brinkley, Proceedings of the 1st International Fall Protection Symposium, Toronto, Canada, International Society for Fall Protection, pp. 51-65 (1988)). By comparison, the tests described herein were conducted on healthy men and women with a mean age of 34 years, and may be more applicable to the general population of construction workers (mean age 37.2 years; “Worker Age in Construction and Other industries.” Section 14 of The Construction Chartbook, Third Edition, 2002. Available at http://www.cdc.gov/eLCOSH/docs/d0100/d000038/sect14.html (last accessed Jan. 12, 2007)). The 75-to-25% ratio for medical-to-voluntary terminations described herein demonstrates that 60 minutes is an adequate suspension time for identifying and measuring improvements in suspension tolerance.
The tests described herein revealed no effects of gender on suspension tolerance. As previously reported (Hsiao et al., Ergonomics, 46(12):1233-1258 (2003)), harness fit was generally worse for women than for men. Harness fit was assessed with subjects standing before being suspended and may not reflect fit during suspension. Appropriate fit and proper wearing of full-body harnesses are essential for successful fall arrest.
In the majority of medically terminated CHEST and BACK tests, the reason for termination was either a decrease in blood pressure or an increase in heart rate, or both. Both body weight and the BACK condition were significantly related to a decrease in MAP, findings that are supported by the results of the Cox analysis of BACK suspension times. Previous research has demonstrated that body weight, as well as height, shoulder width, and stomach girth, can help predict suspension tolerance (Seddon, Harness Suspension: Review and Evaluation of Existing Information, Health and Safety Executive, Research Report 451/2002 (2002)).
The Kaplan-Meier suspension tolerance probability curves (
A major cause of orthostatic intolerance during vertical suspension is the pooling of blood in the veins of the upper legs and in the abdominal and pelvic regions. The support provided to the upper legs, as well as possible compression of the abdomen, by the suspension trauma-prevention fall-arrest apparatus (harness accessory) prevented all medical signs and symptoms during 26 ACCESS suspensions. The 58-minute mean suspension time attained during ACCESS tests is double the mean suspension times observed during CHEST and BACK, and double the full-body harness suspension times reported in previous research (Seddon, Harness Suspension: Review and Evaluation of Existing Information, Health and Safety Executive, Research Report 451/2002 (2002)). While four subjects terminated their suspensions early due to discomfort, 85% of subjects completed the 60-minute suspension. Thus, the suspension trauma-prevention fall-arrest apparatus (harness accessory, or upper and lower body strap assemblies) is effective in preventing the medical signs and symptoms that are precursors to suspension trauma, and it doubled the tolerable suspension time over that tolerable in a conventional harness without the upper and lower body strap assemblies.
In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. I therefore claim as my invention all that comes within the scope and spirit of these claims.
This application claims the benefit of U.S. provisional patent application Ser. No. 60/831,260, filed Jul. 14, 2006, which is incorporated herein by reference.
The present invention was made by The National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, an agency of the United Sates Government. Therefore the United States Government may have certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 60831260 | Jul 2006 | US |
