Tiêu chuẩn iso 16840 2 2007

C040980e book INTERNATIONAL STANDARD ISO 16840 2 First edition 2007 07 15 Reference number ISO 16840 2 2007(E) © ISO 2007 Wheelchair seating — Part 2 Determination of physical and mechanical character[.]

Choice of cushion

Obtain an unused sample seat cushion for testing If a cover is provided, ensure that it is fitted to the cushion in the orientation specified by the manufacturer.

Preconditioning the cushion

Perform the following: a) condition the cushion, unloaded in the test environment for at least at ambient temperature

To ensure optimal performance, adjust the cushion according to the manufacturer's specifications and the applied load using the RCLI It is essential to apply the load with the RCLI for a specified minimum to maximum duration, followed by unloading and reloading within the designated time frame Additionally, remove the load after the specified period and before the next application, allowing the cushion to recover for a minimum to maximum duration.

The loaded contour and seat cushion thickness measurement rig includes components that support a RCLI at the end of a rigid shaft, enabling the RCLI to move forward on the seat cushion within a single plane.

Setup

Perform the following, prior to performing a test method on a cushion.

It is not required to place a cushion between repetitions of the same test method However, if specified by the manufacturer, the cushion should be adjusted to support the applied load.

To ensure optimal performance of the cushion, it is essential to reset it by flattening if it contains a material that remains displaced after loading Additionally, if the manufacturer recommends adjusting the cushion to fit the user's shape, use the specified indenter to accommodate the intended test load Finally, allow the cushion sufficient time to recover fully.

Conduct the tests specified in Clauses 9 to 17 in any sequence.

9 Load-deflection and hysteresis test

Rationale

The load-deflection test assesses the resilience of seat cushions, indicating how well they return to their original shape after being compressed While resilience can be beneficial, as it helps users regain an upright posture when leaning, excessive resilience may push against the body, causing discomfort Conversely, a less resilient cushion may allow for a more stable oblique posture, making it a favorable option in certain situations.

The load deflection test also provides information about the hysteresis characteristics of a seat cushion.

Hysteresis quantifies the energy dissipated by a cushion during loading and unloading cycles, playing a crucial role in impact damping Cushions exhibiting higher hysteresis values are more effective at absorbing energy, particularly on uneven surfaces or when encountering steps, thereby minimizing the transfer of impact energy to the user's body.

Test method

To properly conduct the test, first precondition and adjust the cushion as outlined in sections 7.2 and 7.3 Next, ensure the RCLI is in contact with the test surface supporting the seat cushion, and zero the height gauge to account for the indenter's height Raise the RCLI to position the cushion on the rig's base, ensuring the indenter's ischial tuberosities are either forward of or aligned with the cushion's back edge Apply an initial vertical load and record the height at the RCLI to cushion interface Gradually increase the load within a specified period, waiting to record the height at the same interface after each increment until the total load is reached Repeat this process, increasing the load and recording the height at the RCLI to cushion interface at each stage.

Copyright International Organization for Standardization

Provided by IHS under license with ISO

To conduct the experiment, first, wait and record the height of the cushion at the RCLI to cushion interface Next, remove the last applied loading increment during the unloading period to ensure the total load on the cushion is accurate After this, wait again to record the cushion height at the same interface Continue to remove load within the unloading period, recording the height each time until the total load is adjusted Allow the cushion to recover, and repeat these steps two more times to generate three complete data sets that include both increasing and decreasing loads on the cushion.

The load deflection and hysteresis test can more accurately characterize cushions that quickly respond to load changes when conducted in a continuous loading and unloading manner This involves simultaneous load application and cushion height measurements using an automated test apparatus Refer to the reporting requirements for any deviations from the specified test methods.

Method of calculation

Determine the following: a) The average compressive thicknesses from the three data sets:

— average compressive thickness at b) The average unloading thicknesses:

Test report

a) Report the and hysteresis indices calculated in 9.3 c). b) Plot the average compressive and unloading thicknesses calculated in 9.3 a) and 9.3 b).

Rationale

Some cushions are designed for ease of transfer and others to contain the subject This measurement provides an indication of the slipperiness of the cushion and its cover.

Test method

Apply test methods 12A and 12B specified in BS 3424-10:1987.

Test report

The requirements for reporting results are specified in Clause 16

11 Impact damping under normal loading conditions

Rationale

This test evaluates the features of a wheelchair cushion that minimize tissue impact loading and enhance postural stability The cushion's capacity to absorb vibrations and impacts reduces peak pressures linked to incidents like rolling off curbs or obstacles Impact damping is associated with hysteresis, as detailed in Clause 9.

Test method

Prepare the cushion according to sections 7.2 and 7.3, and perform the tests in the specified order First, position the block beneath the rigid plate to create an angle with the horizontal testing surface Next, place the cushion in the impact damping rig Finally, ensure the IDRCLI contacts the cushion with its ischial tuberosities aligned as intended by the manufacturer.

When using flat cushions, the ischial tuberosities of the IDRCLI are positioned forward of the cushion's back edge To begin the experiment, record the acceleration of the IDRCLI by ensuring the accelerometer is set up to generate a positive signal during its free-fall Finally, slide the block away quickly, allowing the rigid plate to drop onto its rubber stops.

`,,```,,,,````-`-`,,`,,`,`,,` - f) Stop recording after acceleration has diminished to of the maximum. g) Allow between tests. h) Repeat steps d) to f) two more times for a total of three repetitions.

A typical result is shown in Figure 4 with the vertical axis representing the acceleration of the IDRCLI and the horizontal axis representing time in seconds.

The higher frequency components in the acceleration signal exhibit a "ragged" appearance, which is typical and indicative of system vibrations The amplitude of the "first peak" and the threshold are determined using the envelope of the first negative peak.

Y acceleration due to gravity a Block removal and free-fall. b 1st rebound. c 2nd rebound. d 3rd rebound. e of peak at first impact. f Baseline. g Peak at first impact.

Figure 4 — Typical result for impact damping test, plotting acceleration against time in seconds

To assess the damping properties of the cushion, calculate the following parameters: the mean number of rebounds exceeding the peak acceleration, the mean peak rebound acceleration in relation to the baseline, the mean of the second highest rebound acceleration compared to the baseline, and the mean ratio expressed as a percentage.

Rationale

The recovery characteristic of a seat cushion reflects its ability to revert to its original shape and dimensions after being loaded, which can indicate fatigue from repeated use Upcoming developments in ISO 16840 will focus on how cushion properties, including recovery, change over time Some cushions utilize visco-elastic materials that mold to the user's shape and take longer to regain their original form, while others incorporate fluidic components that conform easily to the user but require manual adjustment to return to their initial shape.

Test method

To ensure accurate testing, the cushion must remain stationary throughout the process If movement is necessary for thickness measurements, it should be documented in the test report, and efforts should be made to minimize disturbances Begin by preconditioning and setting up the cushion as outlined in sections 7.2 and 7.3 Next, position the RCLI in the loading rig according to section 5.1 Mark the IT-line on the cushion to align with the ischial tuberostities (ITs) of the RCLI, using the rear edge of the cushion if no clear contour is present Define an IT-reference-point at the intersection of the IT-line and a line parallel to the centerline, located at half the IT spacing of the RCLI Without the cushion, contact the circular platen of the thickness measurement rig with a specified load and record the vertical distance (measurement A) Place the cushion in the static loading rig, ensuring alignment of the ITs and centerlines Center the thickness measurement rig over the cushion at the IT-reference-point, apply a load, and record the vertical distance (measurement B) Apply a specified load with the RCLI and hold for the designated time before removing the load After load removal, center the circular platen over the IT-reference-point again, apply a contact load, and record the vertical distance (measurement C) before finally removing the platen from the cushion surface.

After removing the load, position the circular platen of the seat cushion thickness measurement rig so that it is centered within the radius of the IT-reference point marked on the cushion Apply a contact load and record the vertical distance to the nearest reference plane (measurement D) Repeat this process two additional times for a total of three measurements, ensuring to allow for resetting the cushion between each measurement as specified in section 7.3 b).

Test report

In addition to the information specified in Clause 16, the report must include the two-dimensional location of the IT reference point on the test cushion relative to the mid-line and the back of the cushion It should also indicate whether the cushion was moved during testing to facilitate measurements with the seat cushion thickness measurement rig Furthermore, the report needs to present the average original thickness of the cushion at the IT location (B−A) and the average ratio of the recovery thickness to the original thickness at the IT location.

13 Loaded contour depth and overload deflection

Rationale

A cushion's effectiveness in preserving tissue integrity is linked to its capacity to envelop the pelvis, while ensuring a safety margin in cushioning is crucial to prevent overload conditions Functional movements like leaning and reaching can place excessive stress on the cushion, potentially surpassing this safety margin during transient events.

The overload test evaluates the deflection caused by exceeding the load limit A cushion that has surpassed its safety threshold is recognized when an increase in load fails to yield a proportional rise in deflection.

This test evaluates two key capabilities of cushions: first, their ability to contour based on the initial shape and the deformation caused by loading; second, their capacity to endure conditions of overloading.

Test method

a) Prepare the cushion for testing as specified 7.2 and 7.3.

To perform the loaded contour depth test, preconditioning can be achieved using the LCJ as outlined in section 7.3 Begin by placing the test cushion on a flat, horizontal surface Next, measure the cushion thickness from the horizontal supporting surface to the nearest point at a location near the rear border of the cushion, utilizing the seat cushion thickness measurement rig; for contoured cushions, measurements should be taken at the lateral edge, while convex or flat cushions should be measured at the midline.

NOTE 2 A rigid sheet of material of known thickness can be used to insure a consistent thickness measurement without material deflection; this plank thickness must be subtracted before recording cushion thickness.

Figure 5 illustrates locations of measurement as described. e) Place the LCJ in contact with the cushion so that its ischial tuberosities are positioned at the location intended by the manufacturer.

On flat cushions, the ischial tuberosities of the LCJ are positioned forward of the cushion's back edge A vertical load should be applied, and the vertical distance from the horizontal supporting surface to the inferior surface of the LCJ must be measured to the nearest specified unit Subsequently, the load on the LCJ should be increased.

4 lateral border a Unloaded thickness. b Support surface thickness measured after placement of plank to level fluid/material.

Figure 5 — Measurement method for concave and convex seat cushion top surfaces h

To ensure accurate measurements, re-measure the vertical distance from the horizontal supporting surface to the inferior surface of the LCJ after applying the increased load This process should be repeated two additional times, totaling three measurements, with appropriate intervals and resetting of the cushion as outlined in section 7.3.

a) Using the median and values, calculate loaded contour depth and record to the nearest b) Using the median and values, calculate overload depth and record to the nearest

Test report

The requirements for reporting results are specified in Clause 16.

Rationale

Cushions may be exposed to spillage of liquids or exposure to urine This test determines the time for penetration of liquids through the cover (strike-through).

Test method

Apply methods specified in ISO 9073-8.

Test report

Rationale

Maintaining tissue integrity is crucial, as contact between skin and seat cushion components can lead to complications This testing method outlines the procedure for assessing the biocompatibility of cushion materials that may directly touch the skin during regular use, misuse, or in cases where cushion components fail to contain themselves Additionally, the test aims to confirm biocompatibility when cushion components come into contact with open wounds.

Test method

Apply the test method specified in ISO 10993-1 and ISO 10993-10 to any parts of the seat cushion that has the potential to make contact with the user’s skin.

Test report

The test report must include essential details such as a reference to ISO 16840-2:2007, the testing institution's name and address, the report's issue date, and the manufacturer's name and address It should also specify the model, type, and nominal size of the test cushion, including any serial, batch, and internal tracking numbers Additionally, the report must mention the cushion cover used, the preparation and adjustment of the test cushion, and the characteristics determined in Clauses 9 to 15 Furthermore, it should provide calculations and uncertainty disclosures as per GUM, along with any deviations from the defined test methods.

Manufacturers are required to provide specific details in the specification sheets for each cushion, including the unique model type and nominal size, the cover utilized during testing, and the manufacturing date of both the cushion and the cover.

The RCLI is a modified indenter inspired by Staarink's design from 1995, featuring a geometrically based shape that combines a cone and a sphere to mimic human anatomy The cutting method for the cone and sphere components is illustrated in Figure A.1, while the dimensions and cut lines are detailed in Table A.1.

The fabrication of the RCLI involves several key steps using the dimensions outlined in Table A.1 First, a cone with the specified diameter and taper is turned, followed by dressing the end to create a hemisphere The initial cut is made through the cone, parallel to its tapered edge, and a second cut bisects the plane of the first cut, running parallel to the cone's major axis The resulting two pieces are then positioned as indicated and bonded together A surface finish of at least N7, as per ISO 1302:2002 standards, is applied, and finally, the assembly is attached to a loading rig.

The RCLI is designed to closely resemble adult human anatomy, and it can be easily adapted to represent different anatomical sizes by adjusting its dimensions and the applied loading Future research is expected to confirm the effectiveness of these alternative RCLI sizes.

Figure A.1 — Assembly of components for RCLI

Table A.1 — Cone and sphere dimensions

Anterior- posterior location of load

Cone width at first cut

Length of cone edge mm mm mm mm mm mm mm mm mm

NOTE 2 The RCLI is constructed from cones and spheres machined according to Figure A.1 These components are assembled to form the required shape according to Table A.1.

Wheelchair seat cushions designed to maintain tissue integrity are classified as medical devices Consequently, their features must cater to the specific medical needs of users, rather than conforming to standards set for non-medical applications, such as fire retardancy in furniture.

Concerns have arisen regarding the fire safety of wheelchair seating, particularly the risk of combustion and toxic fume emission that could harm users and those nearby Recent developments show that enhancing the fire resistance of wheelchair seating, particularly polyurethane foam, often involves altering its chemical makeup to comply with fire-resistance standards However, these modifications can compromise the comfort, pressure distribution, and durability of the materials As a result, stringent fire resistance requirements may undermine effective cushion designs and hinder the availability of beneficial products in the market.

ISO 16840 does not specify test methods or requirements for the fire resistance of wheelchair seating It is advisable for manufacturers, purchasers, and users to weigh the risks of tissue trauma or discomfort against the potential for user injury due to fire hazards.

Efforts are ongoing within ISO/TC173/SC1 to establish fire resistance standards that balance the need for pressure ulcer prevention with fire safety The revision of ISO 7176-16:1997 aims to create testing protocols suitable for various applications and environments.

C.1.1 Lateral and forward stiffness rig, a means to support a RCLI at the end of a rigid shaft allowing the

The RCLI is designed to move laterally and forward on the seat cushion within a single plane, featuring a mounting system as outlined in Annex A It includes a pivoting rigid member that can swing in an arc and move vertically within a linear bearing, as illustrated in Figure C.1 Additionally, the system incorporates a restraint mechanism on a rigid base to secure the cushion effectively.

A hook and loop fastening strip or restraint bar along the edge of the cushion base effectively secures the cushion on the test base Additionally, it is essential to apply a vertical load to the RCLI and a force perpendicular to the vertical member, acting within the cushion's plane in both forward and lateral directions, to generate displacement at a specified rate.

; f) the capability of measuring the force applied to the RCLI.

Sliding resistance is a mechanism designed to support a Rigid Cushion Load Interface (RCLI) at the end of a rigid shaft, enabling the RCLI to move forward on the seat cushion within a single plane This system includes a mounting mechanism as outlined in Annex A, features a pivoting rigid member that can swing in an arc and move vertically within a linear bearing, and incorporates a restraint system on a rigid base to effectively constrain the cushion.

To effectively secure the cushion on the test base, a hook and loop-fastening strip or a restraint bar along the edge of the cushion base can be utilized Additionally, it is essential to ensure the system can apply a vertical load to the RCLI and a displacement perpendicular to the vertical member, acting within the cushion's plane Furthermore, the capability to record the force applied to the indenter at a minimum sampling rate is crucial for accurate measurements.

7 Velcro method of restraint under cushion

Figure C.1 — Apparatus to measure lateral and forward stiffness

7 Velcro method of restraint under cushion

Figure C.2 — Apparatus to measure sliding resistance

The measurement of lateral and forward stiffness is crucial in understanding the interaction between seat cushions and skin during slight horizontal force perturbations A cushion's ability to deform in response to body movements is essential, as high shear strain can negatively impact skin integrity While lateral and forward stiffness can influence tissue health even without pelvic movement, a cushion that allows soft tissue to move without shear stress supports tissue integrity However, reduced horizontal stiffness may compromise stability, leading to a trade-off where a cushion with high stiffness offers more stability but increases tissue deformation and shear, while a low stiffness cushion minimizes deformation but may be less stable for the user.

To conduct the test, prepare the cushion as outlined in sections 7.2 and 7.3 Position the RCLI in the lateral and forward stiffness rig, ensuring the cushion is placed correctly under the RCLI, with the ischial tuberosities either forward of the cushion's back edge or aligned with it Apply a specified vertical load to the RCLI and then introduce a lateral displacement at a defined rate Record the peak force and the force applied to the indenter while maintaining the displacement After returning the RCLI to its neutral position, reset the cushion and verify its stability Repeat the measurement process for a total of three trials, allowing for necessary intervals between measurements Finally, reposition the cushion and RCLI for forward displacement and repeat the force application steps.

Tiêu đề	Wheelchair Seating — Part 2: Determination Of Physical And Mechanical Characteristics Of Devices Intended To Manage Tissue Integrity — Seat Cushions
Trường học	International Organization for Standardization
Chuyên ngành	Standardization
Thể loại	international standard
Năm xuất bản	2007
Thành phố	Geneva

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