ISO/DIS 16840-12

Wheelchair seating

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DRAFT INTERNATIONAL STANDARD
ISO/DIS 16840-12
ISO/TC 173/SC 1 Secretariat: SABS
Voting begins on: Voting terminates on:
2021-02-08 2021-05-03
Wheelchair seating —
Part 12:
Envelopment and immersion characterization of seat
cushions using a dual semispherical indenter
ICS: 11.180.10
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
This document is circulated as received from the committee secretariat.
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
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POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 16840-12:2021(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. ISO 2021
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ISO/DIS 16840-12:2021(E)
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© ISO 2021

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ii © ISO 2021 – All rights reserved
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ISO/DIS 16840-12:2021(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Indenter construction ..................................................................................................................................................................................... 2

4.1 Materials ....................................................................................................................................................................................................... 2

4.2 Tolerances and finishes ................................................................................................................................................................... 2

4.3 Indenter elements ................................................................................................................................................................................ 2

4.3.1 Trochanter bar ................................................................................................................................................................... 2

4.3.2 Trochanter blocks ........................................................................................................................................................... 3

4.3.3 Semispherical indenter half ................................................................................................................................... 3

4.4 Indenter assembly ................................................................................................................................................................................ 4

4.5 Sensor locations ..................................................................................................................................................................................... 5

4.5.1 General...................................................................................................................................................................................... 5

4.5.2 Elevation a ............................................................................................................................................................................. 6

4.5.3 Elevation b ............................................................................................................................................................................. 6

4.5.4 Elevation c ............................................................................................................................................................................. 6

4.5.5 Elevation d ............................................................................................................................................................................. 6

5 Instrumentation hardware ........................................................................................................................................................................ 7

5.1 Sensors ........................................................................................................................................................................................................... 7

5.2 Timer ............................................................................................................................................................................................................... 7

5.3 Loading equipment ............................................................................................................................................................................. 7

5.4 Rigid board ................................................................................................................................................................................................. 7

6 Preparation of test cushion ....................................................................................................................................................................... 7

6.1 Cushion set up ......................................................................................................................................................................................... 7

6.2 Preconditioning the cushion to the test environment .......................................................................................... 8

7 Envelopment test method ........................................................................................................................................................................... 8

7.1 Rationale....................................................................................................................................................................................................... 8

7.2 Method ........................................................................................................................................................................................................... 8

7.2.1 Setting the datum height for the indenter ................................................................................................. 8

7.2.2 Pre-conditioning the cushion ................................................................................................................................ 8

7.2.3 Seat cushion thickness measurement ........................................................................................................... 8

7.2.4 Load application and data collection ............................................................................................................. 9

7.3 Calculations .............................................................................................................................................................................................10

7.3.1 Envelopment ....................................................................................................................................................................10

7.3.2 Immersion ..........................................................................................................................................................................11

8 Test report ................................................................................................................................................................................................................11

Annex A (informative) Estimate of measurement uncertainty ..............................................................................................13

Bibliography .............................................................................................................................................................................................................................14

© ISO 2021 – All rights reserved iii
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ISO/DIS 16840-12:2021(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 173, Assistive products, Subcommittee

SC 01, Wheelchairs.

This second edition cancels and replaces the first edition (ISO ISO/TS 16840-12:2015, which has been

technically revised.
The main changes compared to the previous edition are as follows:

— are clarification of technical ambiguities, the removal of a gel cap to protect the pressure sensors,

the removal of a superfluous Annex, and the addition of an Annex giving guidance on the estimation

of uncertainty
A list of all parts in the ISO 16840 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2021 – All rights reserved
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ISO/DIS 16840-12:2021(E)
Introduction

This document provides details of test equipment (an ‘indenter’), and a method, for the measurement

of ‘performance’ of a wheelchair cushion intended to use immersion and envelopment to reduce local

areas of pressure (by effectively supporting more tissue). Primary elements that represent the basic

cushioning effect of a cushion are immersion and envelopment. Immersion into the cushion (the depth

that a body penetrates into the surface) and the envelopment of the body (the intimacy of the cushion

to the body) combine to define the potential cushioning performance of the cushion. Envelopment is

maximized when the variation of forces across the weight bearing surface is minimized. The method

as presented in this document is intended to quantify envelopment and immersion of the body by the

cushion. Alternately, the test method and resulting data can provide an indication of other cushion

construction and seating and positioning strategies, such as strategic pressure offloading.

Issues related to the use of devices that measure interface pressure between the body and a support

surface (e.g. a pressure mapping system) have led to the use of an instrumented indenter, which has

fewer sensors, but sensors which are high quality and exhibit repeatability and accuracy, and thus

reliability.

In this test, the distribution of pressure across the surface of the indenter is evaluated with multiple

indenter sizes and loads. The pressure sensors within the indenter are positioned at multiple elevations

along the buttock form, to simulate and record the pressures experienced at the ischial tuberosities

of the pelvis, the greater trochanters, and at positions along the curve of the buttocks between those

anatomical markers. The review of the values at these various positions, and the variation, or lack of

variation, in the readings, is an indication of the mechanics of the cushion’s interaction with the body

and ability to envelop and protect the tissues.

EXAMPLE A fluid filled cushion with the ability to transfer material between cells may have the potential to

distribute the load to maintain consistent interface pressure regardless of the depth at which the measurement

is taken, as opposed to a foam or other homogeneous surface that behaves more like a spring, in that the greater

the depth of immersion, the greater the interface pressure.

The accommodation of the cushion to the changes in indenter size and load are representative of the

changes in size and mass of the occupant that can occur in the life of a user or between different users.

The indenters are sized to represent changes in size and shape as a user of an approximately 410 mm

cushion gains weight and the size of the buttocks increases. The overall width of the indenters stays

the same, but the size of the semi spheres changes. The loads used in this document approximate to

the 50 percentile user and are not intended to characterize envelopment or immersion under higher

loading conditions, nor to assess the weight capacity of a cushion.

This standard describes test methods which may not be appropriate for all cushions, such as cushions

using anisotropic materials, and therefore, the tester must determine which, if any, are appropriate for

their cushion construction and use.
© ISO 2021 – All rights reserved v
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DRAFT INTERNATIONAL STANDARD ISO/DIS 16840-12:2021(E)
Wheelchair seating —
Part 12:
Envelopment and immersion characterization of seat
cushions using a dual semispherical indenter
1 Scope

This document specifies apparatus, test methods, and disclosure requirements for characterization of

wheelchair seat cushion immersion and envelopment properties using indenters instrumented with

pressure sensors.

This document expands the characterization of products intended to manage tissue integrity

(ISO 16840-2) and provides a standardized indenter for other wheelchair seating tests.

It does not provide information specific to cushion performance for a particular individual user, nor is it

intended to characterize envelopment or immersion under higher loading conditions, nor to assess the

weight capacity of a cushion.

This document includes a method that is specific to 220 mm and 255 mm indenters. Dimensions are

provided for a 380 mm indenter to allow for extension of the method to larger patient simulation.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 1302, Geometrical Product Specifications (GPS) — Indication of surface texture in technical product

documentation

ISO 16840-2, Wheelchair seating — Part 2: Determination of physical and mechanical characteristics of

seat cushions intended to manage tissue integrity
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
base point

lowest point on the curved surface of each of the two halves of the indenter

Note 1 to entry: The base points correspond with the ischial tuberosities on the human pelvis.

3.2
elevation
location of sensors relative to the base points of an indenter
3.3
envelopment
ability to conform, around a shape
© ISO 2021 – All rights reserved 1
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ISO/DIS 16840-12:2021(E)
3.4
immersion
depth from an uppermost plane to which a body penetrates
3.5
offloading

reduction, removal, or transfer of pressure from one area of the body to another

EXAMPLE Reduction of pressure under the ischial tuberosities, but increased pressure on the thighs or

other parts of the seated body.
4 Indenter construction
4.1 Materials

The indenter shall be constructed from hardwood or similar material that is sufficiently rigid so as not

to deform when subjected to the forces required for simulating the application of a human body mass

to surfaces. The indenter material shall be treated (if necessary) to minimize the effects of moisture,

and shall not be adversely affected by normal laboratory testing conditions (0 °C to 35 °C; 25 % to 75 %

relative humidity). Surface finish to be at least N7 (according to ISO 1302, approximate average surface

roughness).
4.2 Tolerances and finishes

Unless otherwise stated, all dimensions in Clause 4 shall be ± 0,5 mm and all edges and corners shall be

finished with a minimum 5 mm radius.
4.3 Indenter elements
4.3.1 Trochanter bar

A 375 mm x 50 mm x 20 mm bar with a series of openings as shown in Figure 1. These openings are for

mounting the indenter halves and trochanter blocks as well as for routing of wires.

Dimensions in millimetres

NOTE Dimension d is the diameter of the pressure sensor selected to meet requirements of Clause 5.1. See

Clauses 4.1 and 4.2 for materials, tolerances, and finishes.
Figure 1 — Trochanter bar construction
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ISO/DIS 16840-12:2021(E)
4.3.2 Trochanter blocks

51 mm × 25 mm × 19 mm blocks as shown in Figure 2, which emulate the trochanters. Each trochanter

bar shall have two trochanter blocks which house the sensors.
NOTE Trochanter bar and blocks are not required on the 380 mm indenter.
Dimensions in millimetres

NOTE Dimension d is the diameter of the pressure sensor selected to meet requirements of Clause 5.1.

Sensor location depth should allow sensing surface to be flush with the indenter surface. See Clauses 4.1 and 4.2

for materials, tolerances and finishes.
Figure 2 — Trochanter block construction
4.3.3 Semispherical indenter half

The semispherical indenter half is a portion of a sphere (see Figure 3). The sphere diameter defines the

size of the ind
...