INTEGRATION OF SLIP RESISTANCE VALUES WITHIN A RISKMANAGEMENT FRAMEWORK: A HUMAN GAIT BASEDAPPROACH USING REFERENCE SAMPLESCarl Strautins and Martin Daniel
Safe Environments Pty Ltd, 4/40 Bessemer Road, Blacktown NSW 2148 Australia

Many slip resistance testing standards assess the relative safety of flooringmaterials by specifying a universal minimum threshold expressed as a Slip
Resistance Value (SRV); limiting the use within a risk management context.
This study contextualises slip related injuries in a simplified risk management
strategy to prioritise slip hazards in conjunction with a broad spectrum of healthand safety related hazards in an occupational hygiene setting. Four reference
surfaces within ASTM F2508 Standard practice for validation and calibrationof walkway tribometers using reference surfaces, were tested by five accredited
laboratories to AS/NZS 4586:2004 Slip resistance classification of newpedestrian surface materials using the pendulum friction tester. The results wereevaluated and categorised in terms of likelihood to evaluate within a risk
assessment matrix along with qualitative descriptors of slipperiness.

Introduction
The Required Friction Demand (RFD) or Ground Reaction Forces (GRF) assessed by subjects
walking across force plates has been well documented (Redfern et al, 2001); however there has
been relatively little evaluation of the GRFs, risk of slipping and the SRVs obtained bytribometers (Powers et al, 2010). This has led to the development of ASTM F2508 which
establishes a validation method to properly rank and differentiate slipperiness of surfaces basedon the incidence of slipping during controlled trials of subjects walking over reference samples ata hurried walking pace (approx. 2.1 m/s), to that of the measurements obtained using atribometer. The purpose of this paper is to validate the results obtained by Powers et al (2010) incontext with a published test method and provide an initial framework to apply a systematic risk
management process to slip related incidents.

Experimental Method
The four reference surfaces as part of ASTM F2508 were tested to AS/NZS 4586:2004
Appendix A Wet Pendulum Test Method using both hardness sliders of 96 (Four S) and 55(TRL). ASTM 2508 requires testing RS A with a surfactant, however testing was conducted withwater for all reference surfaces to maintain consistent test conditions. Each laboratory received
five sub divided samples as part of a simultaneous proficiency testing scheme in line withISO/IEC 17043:2010 Conformity assessment – General requirements for proficiency testing.
The laboratories were accredited to ISO 17025:2005 General requirements for the competence oftesting and calibration laboratories by the National Association of Testing Authorities (NATA).

- 93 -Results
The mean of the inter-laboratory results correctly rank the reference surfaces for both slider 96
and slider 55. There was significant statistical difference (t value > 2.78, paired t test 95thpercentile, df = 4) between each adjacent reference surfaces with the exception of RS A / RS B
for slider 96. This may be due to two laboratories incorrectly ranking RS A and RS B, slider
variability, inter operator error and bias from the calibration facility. For slider 55, all surfaces
were ranked correctly and had statistical significance between adjacent ranking surfaces. Slider
55 being more representative to the human gait based trials which is likely influenced by theshoes being Shore A hardness of 70.
Table 1. SRVs obtained on Reference Specimens when tested to AS 4586:2004 Appendix A
using Slider 96 expressed as a British Pendulum Number (BPN)
Laboratory
12345MeanCI †RS A
171624101716.8
± 6.2

RS B
161625151818.0
± 5.0

RS C
34384325
3535.0± 8.2

RS D636865
6765
65.6
± 2.4

† Confidence Interval (CI) at the 95th percentile, two tailed t – distribution, df = 4

Table 2. SRVs obtained on Reference Specimens when tested to AS 4586:2004 Appendix A
using Slider 55 expressed as a BPNLaboratory
12345MeanCI †RS A16152191214.6
± 5.6

RS B
201726101317.2
± 7.7

RS C
292444172327.4± 12.7RS D
554962595856.6± 6.1† Confidence Interval (CI) at the 95th percentile, two tailed t - distribution, df = 4

Table 3. Calculated t values between reference surfaces (paired t test)
t value
RS A / RS B
RS B / RS C RS C / RS DSlider 96
Slider 55

1.18
3.20

8.72
5.01

9.51
6.97

Discussion
The inter-laboratory variability is practically significant when assessing the upper confidence
limit for purposes of determining compliance with building codes, workplace health and safety
regulations and as evidence relied upon in legal proceedings; the effect being thatrecommendations for SRVs may be overly conservative to account for inter-laboratory variability
which may lead to unnecessary over specification or unjust findings in legal proceedings.
Variability may be reduced through refinement of standardised test procedures, calibrationmethods or the use of reference samples to normalise results across laboratories, such as the useof the ASTM reference surfaces. The verification of improved testing and calibration methods to- 94 -reduce variability should be validated through the use of proficiency testing with accreditation toAS/ISO 17025 and ISO/IEC 17043:2010.
The results reported by Powers et al (2010) for the four ASTM reference surfaces RS A, RS
B, RS C & RS D using the Wessex pendulum were CoF of 0.05, 0.19, 0.24 and 0.49. Thisequates to a BPN of 5, 20, 24 & 46 using the formula provided within Standards Australia HB
197. With the exception of RS B, these results were found to be outside the confidence limits at
the 95th percentile when tested to AS 4586:2004. The differences may arise due to the slider
batches and conditioning protocol, the number of swings over the specimen to record a result andthe calibration methods on the equipment used.
The ASTM 2508 reference surfaces as reported by Powers et al (2010) provide an initialguide as to the risk of slipping at a hurried stride (approx. 2.1 m/s) when unknowingly walking
on a surface wet with water, which tends to be between the SRVs of RS B (4/20 heel slips) andRS C (0/ 20 heel slips). This however is not representative of normal walking pace of 1.3 m/s
observed by Finnis & Walton (2008), thereby providing a factor of safety.
The incidence of heel slips should be used as the basis of the risk of slipping as falls
generally result from the heel slipping during weight transference. Toe slips generally do not leadto a fall; however toe slips can provide important proceciprocal feedback to the individual toindicate that a surface may be ‘detectably slippery’ thereby leading to a reduction in the resultant
GRF and a subsequent reduction in the risk of slipping.
Tables 3, 4, 5 & 6 were modified from a semi-quantitative risk management frameworkoutlined by Firth et al (2006) which is used by the Australian Institute of OccupationalHygienists (AIOH) when assessing a range of physical, chemical, ergonomic and biologicalhazards. The overall risk is contextualised by providing a semi quantitative analysis bydetermining the health impact in combination with the likelihood of the health impact occurring.
The likelihood or risk of slipping can be evaluated by an assessment of the incidence of heel
slips compared with the SRV of reference surfaces. Table 4 provides a summary of thequalitative measure of likelihood based on ASTM 2508, AS/NZS 4586 considering 95thpercentile upper confidence limits of the inter-laboratory testing, Firth et al (2006), Standards
Australia HB 197, Hunter et al (1985) and Powers et al (2010). The SRV in which adisproportionate number of people are likely to slip when walking at a normal walking pace andunknowingly stepping onto a wet surface, is likely to be that offered by RS B. SRVs greater than
RS B form a logical starting point as an ‘unlikely’ event. The SRVs provided are for initial
guidance and are based on upper confidence limits to account for inter-laboratory variability,
which may reduce when assessing individual tribometers with the ASTM reference surfaces.
It is important to qualify that the measures of likelihood are based on the conditions in which
the surface is tested and that of the human gait studies walking on the reference surfaces. In thisstudy, this risk matrix relates to the risk of a person unknowingly walking onto a water wetsurface; the risk would be reduced if a person was already walking on a wet surface as theygenerally should be able to perceive the conditions being wet and potentially slippery and adjust
their gait accordingly. Similarly confounding factors such as foot wear, sloping surfaces,
contaminants other than water, carrying heavy items and the likelihood of contaminants being
present on the floor and perception of those contaminants, will shift the risk profile.
Table 5 assists to categorise the consequences of slipping in perspective of other adverse
occupational health effects as contextualised by Firth et al (2006). Evaluating the qualitative
measure of consequences should a person fall on the level or on stairs, musculo-skeletal injury is
the most probable outcome, being considered level 3 - moderate.
A Health Risk Rating (Table 6) is calculated in context of the likelihood and consequences
which provides recommended actions based on the uncertainty (Table 7). The degree of(un)certainty may comprise: walkthrough audits by personnel experienced in slip resistancetesting (i.e. Bayesian statistics) or the use of surface roughness measurements (Health & Safety
Executive, Slip Assessment Tool) as being highly uncertain; the comparison of SRVs that relate
to the risk of slipping under certain conditions, such as the set of ASTM reference samples(uncertain); or certain, whereby validated statistical SRVs are incorporated within
epidemiological studies to assess the SRV where a disproportionate number slips may be- 95 -expected to occur compared with the background population (relative risk), which takes into
consideration potential confounding factors such as perception of slipperiness.
Where control is required it is recommended to substitute or modify the floor to increase theSRV. Samples of alternative surfaces or identified treatments should be evaluated in terms of theincrease in slip resistance and any other characteristic deemed to be important which may
include; cost, cleanability, mechanical properties, chemical properties adhesion to surface andaesthetics. Ideally a trial of suitable options over time will provide adequate information to
conduct a cost-benefit analysis of the long term sustainable slip resistance.
Proactive management includes active monitoring in conjunction with a combination of soft
control measures such as: isolation (limit access to high-risk areas i.e. restricting access whilecleaning is in progress), engineering methods (reduce water traipsed in during wet weather
through water absorbent matting, apply floor treatments such as acid etching and proprietaryproducts on a regular basis, improve lighting etc.), administrative controls (wet weatherprocedures, provision of umbrella wrapping machines, good housekeeping and adequate cleaningregimes) and personal protective equipment (slip resistant footwear).
Table 4. Qualitative Measures of Likelihood
Suggested Occupational
Hygiene Context

Descriptor

Risk Context

HB 197 Context

A

Almostcertain

Is expected tooccur in mostcircumstances

Extremely slippery;
Safe for short stride andextreme care;
Slip highly probablewithout extreme caution

Less than SRV where allslips occur at normal walking
pace (1.3 m/s).
Possibly < 15 Slider 55 & 96BLikelyWill probably
occur in mostcircumstances.

Noticeably slippery;
Safe for reduced stride
and cautious pace;Non-slip with caution

Between SRV where all slips
occur and SRV where noheel slips occur at normal
walking pace (1.3 m/s).
Possibly between 15 & 25
Slider 55 & 96;

CPossible

Might occur atsome time.

Detectably slippery;
Safe for normal stride,pace and attention; Nonslip with reasonable care

Between SRV where no heel
slips occur and SRV where
no toe slips occur at normal
walking pace (1.3 m/s).
Possibly between 25 & 30
Slider 55 & 96

“reasonably safe”
D

UnlikelyCould occur atsome time.

Non-slip;
Safe for normal stride
and pace and moderateattention;
Non slip at involuntarypace

Between SRV where no toe
slips occur at normal walking
pace (1.3 m/s) and SRV
where no heel slips occur at
hurried pace (2.1 m/s).
Possibly between 30 & 45
Slider 55 & 96

ERare

May occur
only inexceptional
circumstances.

Detectably less slippery;
Safe for hurried stride
and pace and minimal
attention;Non-slip at rapid pace

Greater than SRV where noheel slips occur at hurried
pace (2.1 m/s).
Possibly > 45 Slider 55 & 96- 96 -Table 5. Qualitative Measures of Consequences
Descriptor

RiskContext

Occupational Hygiene
Context

Description of Health Effects

1Insignificant

Noinjuries

Can cause reversible
health effects of little
concern, requiring firstaid treatment at mostMinor irritation of eyes, nose,
throat and/or skin; Minor
muscular discomfort Headaches

2MinorFirst aidtreatment

Can cause reversible
health effects that result in
medical treatment with nolost time

Narcosis; Moderate irritation ofeyes nose, throat and/or skin;
Sea sickness, sunburn, heat rash3

Moderate

Medicaltreatment
requiredCan cause severe,reversible health effects ofconcern – could result in alost time illness

Musculo-skeletal injury; Shortterm physical effects (sunstroke,frostbite)
Nervous systemeffects other than narcosis; Nonfatal airborne disease.

4MajorExtensive
injuries

Can cause a single fatality
or irreversible healtheffects or disabling illness
to one or more persons

Progressive chronic conditions
such as hearing loss,
pneumoconiosis, chronic
obstructive pulmonary disease,
Systemic poisons

5CatastrophicDeath

Can cause multiple
fatalities or significant
irreversible effects

Carcinogens; Reproductivetoxins, Asphyxiants, Life
threatening responses.

Table 6. Health Risk Rating
2 MinorHigh

3 Moderate

4 Major

5 Catastrophic

A

Consequences
1 Insignificant
Moderate

ExtremeExtremeExtremeB

Moderate

Moderate

High

ExtremeExtremeCLow

Moderate

HighExtreme

ExtremeDLow

Low

Moderate

HighExtreme

ELow

Low

Moderate

HighHigh

Likelihood

Active monitoring requires comparing SRVs with incidence of falls to assess where there
may be a disproportionate number of falls occurring to that of the background number of falls;
and auditing controls and/or proactive management strategies in place, ensuring they are effective(such as use of water absorbent matting to reduce water being traipsed into designated dry floor
areas). The results of active monitoring will assist in providing further epidemiological evidence
to assess confounding factors and establish stronger relationships of the incidence of slips
resulting in falls with corresponding SRV’s.

- 97 -Table 7. Recommended actions based on (un)certainty
Health Risk
RatingCertain

Uncertain

Highly uncertain

ExtremeControl needed

Control & Information
Gathering Needed

Control & Information
Gathering Needed

Control & Information
Gathering Needed

Control & Information
Gathering Needed

Information Gathering
NeededInformation Gathering
NeededControl & Information
Gathering Needed
Information Gathering
NeededModerate

Proactive
Management
NeededActive Monitoring
NeededLow

No Action Needed

HighSummaryThe results of inter-laboratory testing for the four ASTM F2508 reference samples to AS/NZS
4586:2004 Appendix A correctly ranked the surfaces for slider 55; however there was insufficient
statistical significance for slider 96 at the 95th percentile between RS A & RS B. Inter-laboratory
variability may be reduced through refining calibration methods such that individual tribometersconform to ASTM 2508 and/or the use of normalising results to known reference samples.
The critical points in the human gait based system are discussed to integrate within a risk
management model. This risk management model provides an initial framework for organisations toprioritise the risk of slip and fall injuries comparably with a range of adverse health effects afforded
through ergonomic, chemical, physical, biological and psychosocial stressors. Epidemiologicalstudies are required to refine and validate the gait-based risk model to allow for confounding factors
in a variety of settings.

References
ASTM International. Standard Practice of Validation and Calibration of Walkway Tribometers
Using Reference Standards (No. ASTM F2508-11). West Conshohocken, PA
Finnis, K.K, & Walton D., (2008) Field observations to determine the influence of population
size, location and individual factors on pedestrian walking speeds, Ergonomics, 51:6, 827842.
Firth, I, van Zanten, D, Tiernan, G (2006). Simplified Occupational Hygiene Risk Management
Strategies. Tullamarine: Australian Institute of Occupational Hygienists Inc.
Hunter, R, Jablonsky, R, Mercher, J (1985), Development of coefficient of friction measurement
methods by consensus –standards-making organizations, Ergonomics 28:7, 1055-1063
Powers C, Blanchette, M, Brault, J, Flynn, J, Siegmund, G (2010) Validation of walkway
tribometers establishing a reference standard, Journal of Forensic Science, 55:2, 366-370
Redfern, M.S., Cham, R., Gielo-Perczak, K., Gronqvist, R., Hirvonen, M., Lanshammar, H.,
Marpet, M., Pai, -Y.C., Powers, C (2001) Biomechanics of slips, Ergonomics, 44:13, 11381166.
Standards Australia (1999). An Introductory guide to the slip resistance of pedestrian surfacematerials (HB 197). Sydney, NSW: Standards Australia.
Standards Australia (2004). Slip resistance classification of new pedestrian surface materials(AS/NZS 4586:2004). Sydney, NSW: Standards Australia.

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