SP-5a: Design Requirements for Wheelchair Integrated Occupant Restraint Systems

Task leader: Linda van Roosmalen, PhD (industrial designer/ rehabilitation scientist)

Co-investigators: Matthew Reed, PhD (mechanical engineer), Miriam Manary (bioengineer/PhD student)

Other participants: Gina Bertocci, PhD (bioengineer, research scientist); Tony DiGiovanni - Hoveround (wheelchair manufacturer/consumers/clinicians); Mark Schmeler (clinician); David Miles, Pittsburgh Rehabilitation Hospital (consumers, pediatrics); Lucy Spruill, United Cerebral Palsy, Pittsburgh (consumers); Mike Nordquist, Sunrise Medical (wheelchair manufacturer)

Duration/ staging of task: This 12 month research task will be conducted in months 1 to 12 of the 60 month RERC cycle



Design of research activities

This specific task will determine the design requirements necessary to develop a wheelchair occupant restraint system that is independent of the vehicle, easy to use and comfortable.

Literature review

In 1994, 154 wheelchair users with spinal cord injury were surveyed concerning the use of safety equipment such as wheelchair tie-downs and occupant restraints (Sprigle, Morris et al., 1994). Sprigle et al. found that 70% of the individuals seated in their wheelchair in a privately owned van reported using wheelchair tie-down systems, but that only 50% of the individuals used occupant restraints. They concluded that 'this lack of occupant restraint use is clearly an issue that must be addressed through improved education and equipment design'. In 1995, 74 individuals using their wheelchairs as motor vehicle seats, reported difficulties with wheelchair securement systems as well as occupant restraint systems in motor vehicles (Linden, Kamper et al., 1996). These studies document the need for more effective wheelchair occupant restraint systems, which are key to improved safety.

The Society of Automotive Engineers (SAE) J2249 WTORS Recommended Practice and the ANSI/RESNA WC19 standard recommends restraint angles and anchorage locations for pelvic and upper torso restraints (SAE, 1996; ANSI/RESNA, 2000). The pelvic restraint should be worn low across the front of the pelvis, and should not be held away from the body by wheelchair components or parts, such as the wheelchair armrests or wheels. The figure below shows proper positioning of the upper torso restraint. Upper torso restraints should fit over the shoulders and should be adjusted as firmly as possible, consistent with user comfort. Finally, restraint webbing should not be worn twisted in a manner that significantly reduces the area of contact of the restraint with the occupant. Unfortunately it is common to not be able to achieve such optimal belt fit due to varying wheelchair sizes, wheelchair obstructions and poor restraint SAE J2249 and ANSI/RESNA WC19 preferred zones for location of shoulder belt on the torso (SAE, 1996; ANSI/RESNA, 2000) anchorage locations (van Roosmalen, Bertocci et al., 1998; Bertocci and Evans, 2000).

A study conducted at the University of Pittsburgh (van Roosmalen, Bertocci et al., 1998) showed compromised belt fit when using a fixed vehicle mounted occupant restraint system (VMRS) for 50th percentile male users, 5th percentile female users and six-year-old children. Another recent pilot study conducted at the University of Pittsburgh, evaluated restraining three power wheelchair users by a trained driver using a vehicle-mounted wheelchair occupant restraint system (VMRS) (van Roosmalen, Bertocci et al., Accepted for publication April 2001). The VMRS consisted of a side-structure mounted upper torso restraint and a floor-mounted pelvic restraint. In all cases as shown in the figures below, wheelchair components or wheelchair-mounted assistive technology were found to interfere with proper restraint usage. Such belt fits have been shown to lead to comprised occupant protection and can even induce injury or fatality (Cocke and Meyer, 1963; Bertocci, Digges et al., 1996; Bunai, Nagai et al., 2001).

Figure at right: Pelvic belt crosses over the armrest of the wheelchair

Figure at bottom left: Pelvic belt crosses the abdominal region of the individual and the upper torso restraint does not contact the shoulder

Figure at bottom right: A failed attempt to use a VMRS on an individual using a power wheelchair equipped with a communication device.

When upper torso restraints do not cross the sternum and do not contact the shoulder, the occupant’s upper body will likely not be prevented from forward movement during a motor vehicle frontal impact (Bertocci, Digges et al., 1996; Bertocci, 1997), which may result in occupant contact with the vehicle interior increasing the potential for injury. When pelvic restraints are poorly positioned and do not cross over the bony prominences of the pelvis, the restraint may slide over the iliac crests and load the soft abdominal tissue (submarining) (as in figures above) (Leung, Tarriere et al., 1982; Viano and Arepally, 1990). Using the ANSI/RESNA WC19 rating system to evaluate restraint fit for wheelchair occupants, all three observations described above would be rated as being ‘poor to fair’ restraint situations (ANSI/RESNA, 2000). Since the observed subjects were all power wheelchair users, this study may not be representative of the general population of wheelchair users in para-transit vehicles. However, it did show that even a well-trained para-transit driver experienced difficulties restraining occupants seated in commonly used power wheelchairs. Again, such poor restraint belt positioning has been shown to lead to increased injury risk and even fatality (Cocke and Meyer, 1963; Dehner, 1971; Bertocci, 1997; Bunai, Nagai et al., 2001).

Results from another survey conducted among 33 wheelchair users showed that individuals using vehicle mounted upper torso and pelvic restraints installed in private vehicles were quick, easy and comfortable to use, but those installed in mass-transit and para-transit vehicles are often perceived uncomfortable, interfering with wheelchair structures, difficult to use and time consuming (van Roosmalen, Bertocci et al., 2001; van Roosmalen, Bertocci et al., Accepted for publication April 2001). This study further highlights the need for improved restraint technology, especially in public vehicle transport. However, since this study utilized such a small sample, additional research is needed to further explore restraint deficiencies among pediatric and adult wheelchair users.

Research objectives

Currently, many wheelchair users find wheelchair occupant restraint systems difficult to use, uncomfortable and provide poor belt fit. Wheelchair seat structure and occupant restraint characteristics influence perceived comfort, ease of use and safety of wheelchair users during transport. This task’s goal is to obtain qualitative and quantitative feedback from the wheelchair using population, their caregivers, therapists, wheelchair manufacturers, seating manufacturers and restraint manufacturers on current occupant restraint deficiencies. Desired features that could be incorporated into future innovative WIRS design concepts will also be sought from these constituents.

The specific objectives in this task are as follows:

  • Objective 1. Develop and conduct a qualitative survey among adult and pediatric wheelchair users to characterize WORS usage patterns, restraint deficiencies and user characteristics.
  • Objective 2. Conduct a focus group of wheelchair users, their caregivers, therapists, occupant restraint and wheelchair and seating manufacturers. Obtain qualitative feedback on proposed conceptual WIRS designs and expand on technical requirements and user needs that were determined from the WORS-user survey. Obtain user ratings on the importance of design features related to manufacturing, assembling and assessing WIRS.
  • Objective 3. Conduct a restraint usability study among pediatric and adult wheelchair users to study and determine design related WIRS user requirements and to quantify the difference in fit and comfort of a WIRS versus a VMRS mockup. WIRS and VMRS mockups (with user adjustable and measurable restraint components and parameters) will be evaluated on usability and comfort by adult and pediatric users.
  • Objective 4. WIRS design characteristics, user needs and technical requirements will be compiled using the Quality Function Deployment (QFD) method (Guinta and Praizler, 1993; Mitra, 1998; Evans and Lindsay, 1999) and disseminated.

Anticipated outcomes

One outcome of this study is to document and communicate current wheelchair occupant restraint deficiencies to wheelchair, seat and restraint manufacturers, and clinicians. Results of the previously conducted WORS survey will be added to obtain a complete picture of current restraint deficiencies. Another outcome of this study will be a QFD matrix, featuring a complete set of product guidelines for the development of adult and child WIRS, based on user needs and manufacturer requirements (hardware, belt paths, anchorage locations etc.). Additionally, the outcomes from this task will function as the basis for Task SP5-b and SP5-c, to develop WIRS design, assessment and evaluation guidelines for manufacturers, clinicians and standards organizations.

References

ANSI/RESNA (2000). Wheelchairs used as seats in motor vehicles. Arlington, VA, RESNA.

Bertocci, G. E. (1997). The Influence of securement point and occupant restraint anchor location on wheelchair frontal crash safety. Bioengineering. Pittsburgh, University of Pittsburgh.

Bertocci, G. E., Digges, K. & Hobson, D. A. (1996). “Shoulder belt anchor location influences on wheelchair occupant crash protection.” Journal of Rehab Research and Development 33(3): 279-289.

Bertocci, G. E. & Evans, J. (2000). “Injury risk assessment of wheelchair occupant restraint systems in a frontal crash: a case for integrated restraints.” Journal of Rehabilitation Research and Development 37(5): 573-589.

Bunai, Y., Nagai, A., Nakamura, I. & Ohya, I. (2001). “Blunt pancreatic trauma by a wheelchair user restraint system during a traffic accident.” Journal of Forensic Science 46(4): 965-968.

Cocke, W. & Meyer, K. (1963). “Splenic rupture due to improper placement of automotive safety belt.” JAMA 183: 193.

Day, H. & Jutai, J. (1996). “Measuring the psychosocial impact of assistive devices: the PIADS.” Canadian Journal of Rehabilitation 9(2): 159-168.

Dehner, J. (1971). “Seat belt injuries of the spine and abdomen.” American Journal of Rontgenology 111: 833-843.

Evans, J. R. and Lindsay, W. M. (1999). The management and control of quality. Cincinnati, South-Western College Publishing.

Gryfe, P. & Jutai, J. (1998). “Assistive technologies: clients' perceptions of impact on quality of life.” Rehab & Community Care Management 7: 26-30.

Guinta, L. R. & Praizler, N. C. (1993). The QFD book: The team approach to solving problems and satisfying customers through quality function deployment. New York, Amacon American Management Association.

Helander, M. G. & Zhang, L. (1997). “Field studies of comfort and discomfort in sitting.” Ergonomics 40(9): 895-915.

Hunter-Zaworski, K. M. (1992). Application of quality functional deployment methods in mobility aid securement design.

Jutai, J. (1999). “Quality of life impact of assistive technology.” Rehabilitation Engineering 14: 2-7.

Leung, Y., Tarriere, C., Lestrelin, D., Hureau, J., Got, C., Guillon, F. & Patel, A. (1982). “Submarining injuries of 3 point belted occupants in frontal crashes.” 821158.

Linden, M. A., Kamper, D. G., Reger, S. I. & Adams, T. C. (1996). Transportation needs: Survey of individuals with disabilities. RESNA annual conference, RESNA Press.

Logan, G. D. & Radcliffe, D. F. (1997). “Potential for use of a house of quality matrix technique in rehabilitation engineering.” IEEE Transactions on Rehabilitation Engineering 5(1): 106-115.

Mitra, A. (1998). Fundamentals of quality control and improvement. Upper Saddle River, Prentice Hall.

Monette, M., Weiss-Lamrou, T. & Dansereau, J. (1999). In search of a better understanding of wheelchair sitting comfort and discomfort. RESNA Annual Conference, Long Beach, CA, RESNA Press.

NHTSA (1999). Advanced integrated structural seat, EASI Eng. & Johnson Controls Inc.

NHTSA, A. (1992). Advanced notice of proposed rulemaking, occupant crash protection, NHTSA, ANPRM,: 22689-22695.

SAE (1996). SAE J2249 Wheelchair tiedowns and occupant restraints (WTORS) for use in motor vehicles, SAE.

Sprigle, S., Morris, B., Nowacek, G. & Karg, P. (1994). “Assessment of adaptive transportation technology: a survey of users and equipment vendors.” Assistive Technology 6: 111-119.

van Roosmalen, L., Bertocci, G. E., Hobson, D. A. & Karg, P. (2001). Usability and satisfaction of wheelchair occupant restraint systems used during motor vehicle transport. RESNA annual conference, Reno, RESNA Press.

van Roosmalen, L., Bertocci, G. E., Hobson, D. A. & Karg, P. (Accepted for publication April 2001). “Preliminary evaluation of wheelchair occupant restraint system usage in motor vehicles.” Journal of Rehabilitation Research and Development.

van Roosmalen, L., Bertocci, G. E., Karg, P. & Young, T. (1998). Belt fit evaluation of fixed vehicle mounted shoulder restraint anchors across mixed occupant populations. RESNA annual conference, Minneapolis, MN, RESNA Press.

van Roosmalen, L., Pogir, H., Bebinec M., Graig, M. & Nordquist, M. (2001). Personal Communication with Sunrise Medical, CO and Invacare, OH.

Viano, D. & Arepally, S. (1990). Assessing the safety performance of occupant restraint systems, Society of Automotive Engineers (SAE).

Zhang, L., Helander, M. G. & Drury, C. G. (1996). “Identifying factors of comfort and discomfort in sitting.” Human Factors 38(3): 377-389.


Progress Report May 1, 2003-2004

A survey and consent form has been developed and approved by both the University of Pittsburgh and The University of Michigan’s Internal Review Board (#0202136). Each survey consists of 38 questions, a consent form, a letter from the participating organization and a pre-posted return envelope. So far, a total of 325 surveys has been send out to the Western Pennsylvania School for Blind Children, the Center for Assistive Technology, Pittsburgh United Cerebral Palsy, Hoveround Personal Mobility Vehicles, University of Michigan Clinic, the Wastenaw School District and the Walter S. Christopher School. A database has been developed in File Maker Pro to document the results from all returned surveys. Follow up calls and mailings were made to collect more survey input from the target group (people who use their wheelchair as a motor vehicle seat).

A focus group study was developed and approved by the University of Pittsburgh’s IRB. The focus group meeting was conducted at the Annual RESNA Conference in Minneapolis (June 26, 2002). Wheelchair/seating manufacturers (Sunrise Medical/Invacare), occupant restraint manufacturers (Sure-Lok), researchers (PITT/UMTRI), clinicians, transit organizations and wheelchair user advocates participated in the 3 hour focus group.

A usability study has been developed and conducted to obtain issues and design characteristics of a wheelchair integrated occupant restraint system for adult wheelchair users. An adjustable frame was developed and equipped with a digital measuring instrument (FARO arm). Wheelchair and occupant data was collected from a variety of 10 wheelchairs and adult wheelchair users. Data acquisition with Excel and digital video recorded wheelchair and occupant measurements as well as seat belt design issues. Data from the usability study is currently being evaluated and used to determine the design direction of integrated restraints for adults versus children.

(Since use input is critical throughout the whole design process (task SP5-b and c) parts of this task (survey) are still ongoing)


Progress Report May 1, 2005

A survey and consent form have been developed and approved by both the University of Pittsburgh and The University of Michigan's Internal Review Board (#0202136). Each survey consists of 38 questions, a consent form, a letter from the participating organization and a pre-posted return envelope. So far, a total of 325 surveys has been send out to the Western Pennsylvania School for Blind Children, the Center for Assistive Technology, Pittsburgh United Cerebral Palsy, Hoveround Personal Mobility Vehicles, University of Michigan Clinic, the Wastenaw School District and the Walter S. Christopher School. A database has been developed in File Maker Pro to document the results from all returned surveys. Follow up calls and mailings were made to collect more survey input from the target group (people who use their wheelchair as a motor vehicle seat). A focus group study was developed and approved by the University of Pittsburgh's IRB. The focus group meeting was conducted at the Annual RESNA Conference in Minneapolis (June 26, 2002). Wheelchair/seating manufacturers (Sunrise Medical/Invacare), occupant restraint manufacturers (Sure-Lok), researchers (PITT/UMTRI), clinicians, transit organizations and wheelchair user advocates participated in the 3 hour focus group.

A usability study has been developed and conducted to investigate usage issues and design characteristics of a wheelchair integrated occupant restraint system for adult wheelchair users. An adjustable frame was developed and equipped with a digital measuring instrument (FARO arm). Wheelchair and occupant data was collected from a variety of wheelchairs and adult wheelchair users (10). Digital video recorded wheelchair and occupant measurements, as well as seat belt usage issues. Data from the usability study is currently being evaluated and used to determine the design concepts of integrated restraints.


Progress Report May 1, 2006

Two concepts of pelvic restraints for adult use have been developed. For one concept additional funding has been sought for technology transfer purposes. For the other concept, we originally had a commercial partner to assist with prototyping. However, due to a conflict regarding a license agreement, this partner has withdrawn from the project. A new partner is now being sought.

One concept is in detailing phase and should be ready for prototyping this summer. Sled testing is expected to take place in the fall of 2006, demonstrating the feasibility of this wheelchair integrated pelvic restraint. The pelvic restraint is innovative because a rotational buckle was used instead of a commonly used push button. Additionally, an adjustable stiff stalk is attached to the buckle to allow for one handed engagement and release.

This project also investigated the feasibility and design criteria for wheelchair-integrated (i.e., wheelchair-anchored) belt-type occupant restraint systems for pediatric wheelchair users, with special emphasis on five-point harness systems for children under 23 kg (50 lb) mass. The initial portion of the project defined design guidelines for integrated restraint harnesses using information from the federal motor vehicle safety standard for child restraint systems (FMVSS 213), from well established principles of occupant restraint, from ease-of-use issues for child restraint systems based on field observations, and from studies of automotive-seated child anthropometry.

During this year, the draft version of these design guidelines was used to implement five-point harnesses obtained from current FVMSS 213-compliant child safety seats on current pediatric commercial wheelchair products. The prototypes were frontal-impact tested to evaluate the crashworthiness of each prototype based on established performance criteria from FMVSS 213. The tests also provided quantitative information on forces applied by harness shoulder belts to the wheelchair seatback for use wheelchair manufacturers in designing their pediatric products for use with fully integrated restraint systems. The final phase of the effort will develop similar prototypes harnesses for lightweight folding wheelchairs.

Based on the information collected during the process of developing and testing these prototypes, the design guidelines were revised and improved, to include strength requirements and issues specific to wheelchair encountered during the prototyping process. These guidelines are now being used to augment ANSI/RESNA WC19 with design and performance criteria for wheelchair-integrated, five-point harnesses for wheelchairs used by children under 23 kg (50 lb).


5 year report June 1, 2006

In the RERC on Wheelchair Transportation Safety, the development, updating, and implementation of voluntary equipment standards are critical activities for achieving the RERC’s long-term outcome or goal of improved transportation safety for wheelchair-seated travelers.  It is through the development and implementation of these standards that the results of RERC R&D activities are translated into the design, marketing, and use of real-world products that are required to provide wheelchair users with a reasonable level of transportation safety and crash protection.

For these reasons, RERC-WTS staff have worked throughout the past 4-1/2 years to provide leadership for the development and revising of both ISO and ANSI/RESNA standards.  In the ISO arena, RERC staff led the development and completion of ISO 10542-3 Wheelchair Tiedowns and Occupant Restraints with Docking Type Tiedowns, which includes the specifications for a Universal Docking Interface Geometry (UDIG). Also, the RERC-WTS staff have been leading the development of ISO 16840-4 Wheelchair Seating Systems for Use in Motor Vehicles, which includes a series of sled impact tests to validate the surrogate wheelchair base (SWCB) as a viable test device for conducting crashworthiness tests of wheelchair seating systems.  Finally, RERC staff have led the development of two New Work Items (NWI), including:

  1. a proposal to revise and upgrade ISO 7176/19 Wheelchairs Used as Seats in Motor Vehicles, which involved the development of a CD draft standard incorporating proposed changes and additions to the existing standard, and
  2. a proposal for a standard addressing rear-facing wheelchair stations in low-g, fixed-route transit vehicles.

Simultaneous with the ISO standards activities, RERC staff have continued to lead efforts to complete the first set of standards to be included in the initial volume of ANSI/RESNA Wheelchair Standards/Volume 4 – Wheelchairs and Transportation, including:

  • WC-18, which is the revised version of SAE Recommended Practice J2249 Wheelchair Tiedown and Occupant Restraint Systems for Use in Motor Vehicles based on experience using SAE J2249 for nearly ten years and including the UDIG,
  • WC19, which is the revised and updated version ANSI/RESNA WC19 Wheelchairs used as Seats in Motor Vehicles
  • WC-20 a new standard for Wheelchair Seating Systems for Use in Motor Vehicles, which is comparable to the ISO 16840-4 

In support of developing WC-20, validation testing of the SWCB was completed using four different commercial seating systems and a sling seat and seatback tested on both the SWCB and a commercial manual wheelchair.  Results of these tests confirm that testing of seating systems on the SWCB produces similar, but somewhat worst-case, seat and seatback loading and failures during frontal impact testing, and thus confirms that testing seating systems using the SWCB provides a viable method for evaluating seating system performance for use on a wide range of wheelchair bases.

In addition to these three standards, related documents that contain specifications and engineering drawings for test facilities have been updated for inclusion in Volume 4. These include:

  • the surrogate wheelchair (SWC),
  • the four-point surrogate tiedown systems (4-pt SWTORS),
  • the surrogate UDIG docking tiedown device (SUDIG WTORS), and the
  • surrogate wheelchair base (SWCB)

Finally, the results of Task 2a have been used to develop a draft wheelchair standard for rear-impact of forward-facing wheelchair seated occupants (RIFF), including preliminary test methods and performance criteria.  These requirements and test methods will be included in a separate part and future version of Volume 4.

With regard to the implementation of standards (Task 6c), there has been a significant effort throughout the past four years to develop and disseminate information that will inform and educate various interest groups about the existence of crashworthiness wheelchair and WTORS standards, and to answer questions from manufacturers and consumers about the standards and other issues related to safe transportation for wheelchair travelers.   In addition to numerous individual communications via email and phone conversations, and direct contact with numerous wheelchair and WTORS manufacturers through product testing to these standards at UMTRI, RERC staff have given numerous presentations and workshops and the RERC-WTS website has been updated with new information on standards activities and other educational materials.  In addition, the list of wheelchair products that comply with current ANSI/RESNA WC19 has been periodically updated.

A key tool for disseminating information about wheelchair transportation safety and encouraging the use of products that comply with the ISO and ANSI standards has been the Ride Safe brochure. This brochure was revised and updated during the past year and the updated version is now available on www.travelsafer.org.  Over 75,000 Ride Safe brochures have now been distributed and several wheelchair manufacturers are including them with all WC19 wheelchairs and distributing the brochures at trade shows and conferences.  

A significant step toward increasing the implementation of products that comply with the current standards was made in the development and discussion of the Theme-1 white paper at the RERC-WTS State-of-Science (Sos) Workshop held January 2005. The title of this theme was Barriers to the Development, Marketing, Purchase, and Use of Transit Safety Technologies, or TST, where the latter term refers generically to equipment that complies with voluntary WTORS and WC19 wheelchair standards.  

The discussions on this topic identified the primary barriers to increased availability of WC19 wheelchairs, which include:

  1. A broad lack of knowledge and awareness of the standards and products that comply with the standards
  2. Manufacturer’ fear of liability
  3. Lack of economic incentives for manufacturers
  4. The voluntary nature of the standards

Overall the top three strategies for dealing with all of the identified barriers to TST were:

  1. Create regulations that make the presence and use of TST mandatory
  2. Educate transit providers, third party payers, users, government agencies regarding the value of TST including the cost of injury vs. the cost of providing TST (i.e., cost benefit analysis)
  3. Develop the concept that wheelchair transportation safety is an integral feature and therefore should be included into the base price of transit wheelchairs

In follow up to the SoS and these identified strategies, RERC staff have been actively involved in getting CMS codes assigned to most categories of powered wheelchairs to include reference to ANSI/RESNA WC19.  When the opportunity arises in the next few months, RERC staff will work to have WC19 referenced in CMS codes for both adult and pediatric manual wheelchairs.

Another important outcome of the SoS workshop resulted from a discussion with Dennis Cannon of the Transit-Access Board regarding opportunities to provide input with regard to changes to ADA requirements for wheelchair securement and occupant restraint in different types of public transit vehicles.  In response, a new Breakout Group of the RESNA Committee on Wheelchairs and Transportation (COWHAT) was formed and convened its first meeting in February to establish a plan for providing recommendations for changes to ADA that will improve both safety and efficiency in public transportation of wheelchair users.

In a further effort to reach constituent groups with information about transportation safety for wheelchair-seated travelers and standards for equipment used in transporting wheelchair users, formal connections between COWHAT and the National Mobility Equipment Dealers Association (NMEDA – i.e., the organization of vehicle modifiers for people with disabilities) and the American Public Transit Association (APTA) have been, or are the process of being, established.  Subcommittees established within these organizations will provide the means for these constituent groups to interpret and disseminate information on the standards and related best practice as appropriate to their respective transportation environments, as well as for providing input to the development of future standards and revisions of existing standards. In addition, RERC staff have continued to maintain contact with national organizations that oversee school transportation safety and recently provided revisions to the section of the National School Transportation Specifications and Procedures manual dealing with “Specially Equipped School Bus Specification.”

Last updated: August 18, 2006

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