FprCEN/TR 18249
(Main)Head protection - Scientific background and rationale to EN 17950
Head protection - Scientific background and rationale to EN 17950
This document describes the scientific background and rationale for the content of EN 17950, Protective helmets - Test methods - Shock absorption including measuring rotational kinematics.
Kopfschutz - Wissenschaftlicher Hintergrund und Begründung zu EN 17950
Zaščita glave - Znanstveno ozadje in utemeljitev EN 17950
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-november-2025
Zaščita glave - Znanstveno ozadje in utemeljitev EN 17950
Head protection - Scientific background and rationale to EN 17950
Kopfschutz - Wissenschaftlicher Hintergrund und Begründung zu EN 17950
Ta slovenski standard je istoveten z: FprCEN/TR 18249
ICS:
13.340.20 Varovalna oprema za glavo Head protective equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
FINAL DRAFT
TECHNICAL REPORT
RAPPORT TECHNIQUE
TECHNISCHER REPORT
August 2025
ICS 13.340.20
English Version
Head protection - Scientific background and rationale to
EN 17950
Kopfschutz - Wissenschaftlicher Hintergrund und
Begründung zu EN 17950
This draft Technical Report is submitted to CEN members for Vote. It has been drawn up by the Technical Committee CEN/TC
158.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
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.
Warning : This document is not a Technical Report. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a Technical Report.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. FprCEN/TR 18249:2025 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
Introduction . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Reasons behind the choice of test method . 6
4.1 Background . 6
4.2 The importance of the cervical spine and body . 7
4.3 Impact anvil . 7
5 Headform . 8
5.1 General . 8
5.2 Moment of Inertia (MOI), mass and centre of gravity . 8
5.3 Head shape . 14
5.4 Coefficient of friction between headform and helmet . 19
6 Evaluation of the test method and headforms . 20
7 Summary . 25
Annex A (informative) Data used for the centre of gravity vs. circumference . 26
Annex B (informative) How the neck affects the head kinematics . 29
Bibliography . 31
European foreword
This document (FprCEN/TR 18249:2025) has been prepared by Technical Committee CEN/TC 158
"Head protection", the secretariat of which is held by SIS.
This document is currently submitted to the Vote on TR.
Introduction
The objective of this document is to provide the scientific background and rationale for the content of
EN 17950:2024[1] Protective helmets — Test methods — Shock absorption including measuring
rotational kinematics. EN 17950:2024[1] that was developed by Working group 11 (WG 11),
Headforms and test methods within the CEN, the European Committee for Standardization, Technical
Committee CEN/TC 158, Head protection.
The main reasons for developing a new rotational test method were:
— Oblique impacts are more frequent than pure linear impacts, see [2], [3], [4], [5] and [6]. In case of
an oblique impact and if the coefficient of friction is high enough, the tangential force could result
in an additional rotation of the head.
— Several studies show that the human head is sensitive to rotational motion, see [7], [8], [9], [10],
[11], [12], [13], [14], [15] and [16].
The first discussions within CEN/TC 158 to develop a standard with a rotational test method for helmets
was initiated 2006 and the new standard EN 17950:2024[1] was published in July 2024. During the
development of EN 17950:2024[1], WG 11 produced around 500 documents, performed numerous of
experimental tests, and held a large amount of meetings with its experts from a variety of CEN members.
These experts represented organizations from, among others, helmet manufacturers, universities, test
institutes, government authorities, consumer organizations, and research institutes.
In 2013, a project plan for the development of a new test method was created. The scope of the new test
method were in short:
a) measure head kinematics for impacts that induce rotational motion against a hard surface;
b) be simple, robust and cost effective,
c) use impact conditions based on real accident data,
d) be adjustable for several helmet categories.
Clause 4 presents potential test methods and the reason for the choice of test method used in EN
17950:2024[1]. The reason for not using a mechanical neck is described in 4.2 and the motivation of
choice of impact anvil and impact angle is presented in 4.3.
WG 11 also reached consensus that the headform according to EN 960:2006[17] was not suitable for a
rotational test method due to the fact that its inertial properties are not correct for rotational impacts
[18]. WG 11 was also discussing using the Hybrid III (HIII) headform. The main reasons for not adopting
the HIII headform were lack of sizes, specification of the Moment of Inertia (MOI), too high coefficient
of friction (COF) between the HIII rubber and comfort padding, and absence of a portion of the neck
which should constrain the chin strap, particularly under rotational impacts [19].
Therefore, WG 11 reached consensus to develop a new headform for inclusion in EN 17950:2024[1]
with the following attributes to all head sizes defined by the circumference in cm:
e) a biofidelic MOI around all three principal axes;
f) a biofidelic mass;
g) a biofidelic outer geometry;
h) a biofidelic outer surface interface with the comfort padding in the helmet (coefficient of friction
between the head and the comfort padding in the helmet).
Clause 5 describes the background to the headform specification in EN 17950:2024[1]. An evaluation
of the test method and the headform was performed to evaluate the repeatability and reproducibility
between individual tests and between different test laboratories. This evaluation is further described
in Clause 6.
Since the plan to develop EN 17950:2024[1] was to make it adjustable for several different helmet
categories, the impact velocity and impact location are not specified within EN 17950:2024[1]. A list of
examples of references to different studies, which WG 11 used as support material during the
development of EN 17950:2024[1] regarding these factors, are listed in Table 1.
Table 1 — Example of publications concerning accident data
Helmet categories Reference
a
Bicycle
[20] , [5], [3]
Horse riding [21], [22]
a
Industrial
[23]
Snow [24], [25], [26]
a
This source was published after the development of EN 17950:2024[1].
The pass/fail metric and threshold values have also been discussed in several meetings. It was however
decided to not include recommendations for the pass/fail criteria in EN 17950:2024[1]. One item for
discussion was to record the three linear and three rotational metrics versus time to enable the
computing of advanced brain injury metrics in the future.
1 Scope
This document describes the scientific background and rationale for the content of EN
17950:2024[1], Protective helmets — Test methods — Shock absorption including measuring rotational
kinematics.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
4 Reasons behind the choice of test method
4.1 Background
WG 11 identified several different test methods to evaluate rotational impacts:
— Dropping the helmet positioned on an instrumented headform against an oblique surface and
measuring the tangential force between the helmet and the impacting surface, see [27].
— Dropping a helmet positioned on an instrumented headform against an oblique surface and
measuring the kinematics of the headform, see [28] and [29].
— Dropping a helmet positioned on an instrumented headform against a horizontal plate that is
moving at a controlled speed and measuring the kinematics of the headform, see [30] and [31].
— Dropping a mass onto a headform that is attached to a neckform, see [32].
— A pneumatic impactor that is impacting the helmet positioned on a headform that is connected to
a neckform and measuring the kinematics of the headform, see [33] and [34].
The method of dropping the helmet and headform against an oblique surface and measuring the
tangential force was proposed in ECE 22.05 [27] and referred to as method A. The test method was
designed to measure the tangential force between the helmet and the impacting plate that is angled 15°.
The advantage of dropping the helmet against an oblique surface is the simplicity of having just one
part moving, the helmeted headform. Another advantage is the simplicity of measuring the tangential
and the normal force in the plate as it is an inexpensive solution instead of having a number of
accelerometers and/or rotational transducers in the headform. However, it has been shown that the
tangential force in the plate cannot measure the energy absorption in the helmet as a six-degree of
freedom instrumentation in the headform can [35]. A possible improvement of the test used in ECE
22.05 [27] is to change headform specified and install sensors that can measure the six-degree of
freedom, for example using accelerometers or a combination of accelerometers and rotational rate
sensors. Further, the 15° inclined anvil leads mainly to sliding and does not permit an effective tangential
loading of the helmet structure.
The method of dropping the helmeted headform against an oblique surface was first presented by Deck
et al. [28]. They proposed to drop a helmeted headform against an 45° oblique surface relative to the
ground and measuring the six-degree of freedom kinematics of the headform. This test method has the
advantage of using a vertical drop tower, which is already used for shock absorption testing according
to EN 13087-2:2012[36]. The changes required to perform the tests against an oblique surface are
minor.
The method of dropping the helmeted headform against a horizontally moving plate has been proposed
in several studies, see [37], [38] and [39]. One of the advantages with this method is that it is easy to set
different combinations of impact speeds and impact angles. One limitation is that the test is more
complex compared to dropping the helmeted headform against an oblique surface and therefore is more
expensive.
The method of dropping a mass vertically towards the helmeted headform attached to a neckform was
described by Siegkas et al. [32]. There are benefits with this test method as it is easy to control the initial
position of the head and helmet. However, as described in 4.2 the HIII neck has its limitations and also
that the test machine adds complexity and costs.
The method of using a pneumatic impactor has been used by National Operating Committee on
Standards for Athletic Equipment (NOCSAE) [33] and National Football League (NFL) [34]. In the
NOCSAE test setup, they are using a linear impactor (14 kg) that is accelerated by a pneumatic cylinder
to hit the HIII headform, which is attached to the HIII neckform, see [33]. One limitation with this test
method is the use of the HIII neckform, which has shown to be relatively stiff compared to human
data, see [40]. Another limitation with this setup is that several of the impact points go through the
centre of gravity of the headform, which results in that the larger contribution of the rotational motion
is induced by the flexibility of the neckform and not the tan
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