Research into the forces required to open paper and sheet ...ergo-eg.com/uploads/books/forces required to open paper.pdf · and sheet plastic packaging – experiments, results and

Research into the forces required to open paperand sheet plastic packaging – experiments,results and statistics in detail

Carried out under contract to the DTI by:

Robert Feeney Associates (RFA) Product Safety and Testing GroupLinden House Division of Manufacturing and Operations ManagementThe Old School Playground University of Nottingham1 Butthole Lane University ParkShepshed NottinghamLeicestershire NG72RDLE12 9BN

Table of contents

Main report - Research into the forces required to open paper and sheetplastic packaging ..................................................................................................................3

1. Introduction..................................................................................................................3

2. Stage 1. Background study..........................................................................................32.1 Objectives ..............................................................................................................32.2 Review of existing data on peel-back and tear type package opening behaviour

and on people’s peel and tear strength...................................................................32.3 Investigation of packages of different types ..........................................................42.4 Focus groups for peel-back and tear packaging.....................................................42.5 Detailed study of the strategies used by non-disabled and disabled consumers

when opening selected packages ...........................................................................52.5.1 Pilot study ......................................................................................................52.5.2 Main study .....................................................................................................62.5.3 Procedure .......................................................................................................6

2.6 Conclusions from Stage 1 ......................................................................................82.6.1 Measuring equipment for peel-back and tear type packaging.......................82.6.2 Experimental design for Stage 2..................................................................11

3. Stage 2. Data collection.............................................................................................113.1 Objectives ............................................................................................................113.2 Peel-back packaging experiments........................................................................11

3.2.1 Equipment....................................................................................................113.2.2 Preliminary study.........................................................................................123.2.3 Main study ...................................................................................................133.2.4 Results .........................................................................................................163.2.5 Analysis .......................................................................................................233.2.6 Concluding remarks from peel-back experiment ........................................263.2.7 Implications for packaging design...............................................................28

3.3 Tear packaging experiments ................................................................................283.3.1 Measuring equipment for tear type packaging ............................................283.3.2 Preliminary study.........................................................................................293.3.3 Main study ...................................................................................................293.3.4 Results .........................................................................................................343.3.5 Analysis .......................................................................................................393.3.6 Concluding remarks from tear experiments ................................................403.3.7 Implications for packaging design...............................................................41

3 References...................................................................................................................43

Research into the forces required to open paper and sheet plastic packaging –experiments, results and statistics in detail.

1. Introduction

This report describes research carried out under contract by Robert Feeney Associates andNottingham University for the Department of Trade and Industry. The research wasconducted in two stages. The aim of the first stage was to investigate behaviour used bypeople when opening paper and plastic sheet packages that require a tearing or peel-backaction and hence be able to specify the equipment needed to measure people's strength whencarrying out such actions. The second stage was to design and construct such equipment andcollect data on people's strength capability when opening paper and plastic sheet packaging.The resulting data are aimed at designers of packaging to ensure that the forces required toopen packaging will be within the known capabilities of the general population and inparticular, older persons. The focus in the research was therefore primarily on older peoplebut with data also collected on a small number of disabled people and non-disabled peopleunder 50 years of age.

2. Stage 1. Background study

2.1 Objectives

• to identify the different types of tear and peel-back packages available

• to identify package types of interest i.e. those that present difficulty and for whichrecommendations for opening forces need to be defined

• to identify the strategies used by consumers and hence specify the equipmentneeded to measure people’s force limits.

2.2 Review of existing data on peel-back and tear type package opening behaviour and onpeople’s peel and tear strength

Very little information on actual package opening behaviour was found during a literaturesearch.

Previous studies have demonstrated that older people and disabled people appear to be mostaffected by poor packaging design (DTI, 1997, 1999a, 1999b, 2000, 2002). Information fromHASS data (199b) gave an insight into which packages posed greatest difficulties andrequired tools to open, and more specifically information on accidents involving plasticpackaging (1999a).

Design data published by the DTI (1999b) shows that force exerted on different tasks variesvery little between the ages of 16 and 50 years. Thereafter there is a rapid decline in the forceindividuals can exert. Research concerned with all age groups therefore would give resultsbiased towards the majority group i.e. those aged 50 years or less. If such results were usedfor the design of packaging it would disenfranchise a large proportion of the elderlypopulation.

Information from the packaging industry was also reviewed. Again little information ofrelevance to this project was found. It is interesting to note that tear strength is defined as ‘amaterial’s resistance to tearing’. In practice this is the amount of force, as measured in atensile test rig, required to continue a tear once a nick or cut has been introduced in the edgeof the material. The test which is carried out by the Packaging Industry Research Association(PIRA) requires a 50 mm cut before the strength is measured. This method is only for testingtear strength, not peel-back and these methods are very crude and not comparable to thebehaviour of individuals when tearing real packaging.

Anwall (1974) in a survey of 428 adults in Sweden demonstrated that ease of opening ofpackages was the most important package characteristic. The packages most criticised inAnwall’s report were examined in a preliminary study by Ivergard (1978). This involved asmall number of adults (n = 60 approx.) including some older persons and disabled persons.Ivergard also carried out a pilot study to measure the forces that could be applied to a numberof different package types including washing powder cartons with tear strips and push/tearperforations. The main purpose of this study was to establish procedures and developsuitable instruments for a larger study. Drawing on these investigations Berns (1981)concluded that the torques and compressive forces that people can apply to opening packagescould be measured objectively. He also concluded that there are great differences in thetorques and forces that can be applied by the general population compared with those of thedisabled population particularly those with rheumatic conditions.

2.3 Investigation of packages of different types

Packages from supermarkets and other stores were investigated in order to examine the rangeof basic designs available to consumers. The results of this investigation found that there arethree basic tear and peel-back type packages available. These are:

• plastic, paper and foil cartons and sachets

• plastic and paper bags

• foil and plastic containers with plastic or foil peel-back covers

Within these categories there are a variety of sizes, materials and different methods ofopening.

2.4 Focus groups for peel-back and tear packaging

The purpose of the Focus Groups was to analysis in general the strategies used by peoplewhen opening different packages and to get information from people on the difficulties theyexperienced and for general orientation. Six packages were chosen to represent the range ofproducts identified in the previous stage.

Two focus groups were organised, one comprised six people over 65 years of age, the othercomprised six people, between X and 35 years of age. It was assumed that people of widelydiffering ages would exhibit different opening strategies, primarily due to the differentstrength capabilities.

The packages chosen were as follows:

• muesli (bag of cereal)

• cheese packet

• toilet freshener (plastic needing to be torn from cardboard)

• orange juice carton (tear line along spout)

• ham (peel-back)

• corned beef (no access)

The participants in each group were seated around a table with the video camera at the headof the table. Each of the packages was presented in turn to half of the group on one side ofthe table, who were then asked to open the package. Each person in the other half of thegroup was asked to observe the person opposite opening the packages. A knife and pair ofscissors were placed on the table and the participants were asked only to use them as a lastresort. During and after opening the packages the participants, (both those opening packagesand those observing) were encouraged to discuss their experiences and observations. Thetwo halves of the group then reversed roles and the procedure was repeated. The wholesession was video recorded for later analysis.

From the video recording it was also possible to analyse how people actually openedpackages. This was complimented in some cases by the description they gave of theiractions. Problems seemed universal to both age groups although accentuated to some degreefor the older participants. Areas that caused most problems were small and slippery gripareas and where packages were sealed too strongly.

This information was used to find packages that posed particular problems and also to gain aninsight into the specific ways in which individuals might be video recorded for the mainbehaviour study. The best angle for analysis appeared to be from in front of the participant.This reduced the amount of interference from hands and parts of the package obstructing theview in order to include a comprehensive range of packages.

It was further concluded that accurate monitoring of behaviour could only be achieved if theconditions under which the packages were to be opened were as ‘natural’ as possible.

2.5 Detailed study of the strategies used by non-disabled and disabled consumers whenopening selected packages

2.5.1 Pilot study

For the purpose of this study four elderly participants aged over 65 years were selected.

Samples of cartons or sachets were selected to represent packages that needed to be openedby the different methods identified in the Focus Groups. They included package types thatcould be opened by simply tearing (for example from an edge), those which required openingby pulling apart using two hands and those which required peeling back a cover.

A small worktop and cupboard of a standard height were used to represent the conditionssimilar to those which would normally be found in the kitchen environment. The packageswere placed inside the cupboard and the participant was instructed to open the cupboardunderneath and remove the packages one at a time. Participants were asked to open the

package as they would normally. A video recording was made for each package opened.The camera was set up directly in front of the participant. Every attempt was made to focusthe participant’s attention away from the video recording and onto the actual task at hand,therefore encouraging the most natural behaviour.

The video recordings for each participant were analysed using a slow motion and freezeframe technique to identify the number of grips, type of grips and the specific technique usedby the participant with each hand to open each package.

From this study packages were identified for inclusion in a main study and which representedthe types and grips and strategies used by people when opening plastic and paper packaging.The study also confirmed the recording and analysing procedure to be used in the main study.

2.5.2 Main study

The purpose of the main study was to specifically identify the type of grips used whenopening paper and plastic packaging as a preliminary to designing equipment to measurepeople’s strength capabilities in package opening.

Two main groups of participants were included in the study, namely those with handimpairments and those without.

The non-impaired group was separated into three age categories. There were six participantsaged 15 and less, eight participants aged between 18 and 50, and six participants aged over65.

The group with hand impairments comprised fourteen participants with a range ofdisabilities, aged from 23 to over 70 years old. These were selected on the basis of severityof hand / arm impairment to represent the extremes of characteristics likely to be found in thegeneral population. The distribution included arthritis, cerebral palsy, and multiple sclerosis.

The packages chosen for the final study comprised packages of various sizes and weights thatwere commonly available in retail shops.

For tearing the following packages were chosen:

• one carton type package

• one sachet type package

• four bag type packages (of different sizes)

For peel-back, the following packages were chosen

• three single tab

• three double tab

The packages chosen are shown in the Appendix 1.

2.5.3 Procedure

The procedure used was the same as employed in the pilot study (Section 2.5.1). Theparticipants were video recorded opening each item. However while the procedure in the non

impaired group followed the procedure in the laboratory, the participants in the impairedgroup were visited and observed in their own settings. For both the home and laboratorysituation, the packages were handed to the participant in a shopping bag. The participant thenhad to remove them from the bag, place them in a cupboard and then one at a time, removethem from the cupboard and open each packet. In each case the opening task was videorecorded.

Video recordings of the strategies and behaviour used were then analysed in order to producea classification for general techniques and grips.

The study demonstrated that there are differences in package opening behaviour betweenindividuals regardless of age. There are however normal age related differences in packageopening with younger people relying more on greater grip force and pull strength whilst theolder people tend to be more influenced by cultural factors. For example older participants,to whom modern sophisticated packaging had been introduced over a number of years,tended to search for opening instructions or look for opening features. It was also concludedthat individuals use different techniques to open different packages and different individualsuse different techniques to open the same packages.

Fundamental to the analysis were the different types of grips that people use whenmanipulating packages, these are:

• power grip

• lateral grip

• three finger chuck

• finger pinch

The grips used, the package orientation and technique employed for tear type packaging areshown in Table 1.

grip packageorientation

strategy technique (1) technique (2)

power grip vertical grip each side straight pull pivoting the wrist

lateral grip vertical grip each side straight pull pivoting the wrist

three finger chuck vertical grip each side straight pull pivoting the wrist

finger pinch vertical grip each side straight pull pivoting the wrist

Table 1: Grips used, the package orientation and technique employed for tear type packaging

For tearing open bag-type packages, the analysis showed that all of the different grips wereused. Two main techniques were employed, namely;

• a straight opposing pull outwards

• pulling with the wrists acting as a pivot

The analysis also showed that when tearing open packages the packages were alwayspositioned vertically.

For peeling back all the above grips were used except the power grip.

With these grips, four strategies were used, namely:

• gripping two tabs packet vertical (i.e. hanging down)

• gripping two tabs packet horizontal (i.e. on work-surface)

• gripping one tab and holding packet down on work-surface

• gripping one tab with packet held in other hand

Again, the techniques used were a straight pull and pulling with the wrist rotating whilepressed against the package.

The grips used, the package orientation and technique employed for peel-back typepackaging are shown in Table2.

grip packageorientation

strategy technique (1) technique (2)

finger pinch, lateral orthree finger chuck

vertical gripping two tabs straight pull None


horizontal gripping two tabs straight pull rotating the wrist


on worksurface

gripping one tab straight pull rotating the wrist


held in otherhand

gripping one tab straight pull rotating the wrist

Table 2: Grips used, the package orientation and technique employed for peel-back type packaging

Many of the problems were exacerbated for the disabled participant. The size of the tabs andthe texture of the material played a much greater role for them as they were naturally lessable to grip. They were also more affected by the size weight and shape of packets. Thiscaused them to have to grip the packages in unusual ways (i.e. tilting and turning) in order toget the required strength for gripping and peeling back. They used more repetitive smallmovements, as they often could not open the packages in one motion. These movementswere made so as to loosen the seal, weaken the material, or tear the material in stages. Theuse of teeth and tools occurred quite often. Frequently however, the participant gave uptrying.

The need for clear instructions was of greater importance for disabled people who often didnot have the flexibility for using straightforward robust techniques i.e. simply pulling thepackage apart.

2.6 Conclusions from Stage 1

2.6.1 Measuring equipment for peel-back and tear type packaging

2.6.1.1 GeneralPrevious studies have demonstrated that older people and disabled people appear to be mostaffected by poor packaging design (DTI, 1997, 1999a, 1999b, 2000, 2002).

As regards the effect of age, design data published by the DTI (1999b) shows that forceexerted on different tasks varies very little between the ages of 16 and 50 years, thereafter

there is a rapid decline in the force individuals can exert. Research concerned with all agegroups therefore would give results biased towards the majority group i.e. those aged 50years or less. If such results were used for the design of packaging it would disenfranchise alarge proportion of the elderly population. The proposed research should thereforeconcentrate on the over 50 years age groups. It was accepted however that a small number of16 to 50 year olds should be included to provide baseline results for comparative purposes.

The Stage 1 study also showed that the requirements of disabled people are more complexand more demanding than those of non-disabled people. In order to take their needs properlyinto consideration it was concluded that a much more detailed study would need to beundertaken. The approach therefore to be used in designing equipment to measure strengthcapabilities in opening packages, is to place the emphasis on the needs of non disabled peoplewhile, as far as possible, taking cognisance of disabled people, as much as they are known atthis stage.

The Stage 1 study demonstrated that there are some strong behavioural trends that enableconclusions to be drawn as to the techniques that are commonly used for opening packages ofdifferent types. Hence it should be possible to specify the type of strengths that need to bemeasured. In order to focus on the design of the equipment, sketches were produced of someof the main grip types and techniques that were identified (Appendix 2). They demonstratedthe importance of designing the equipment to be as realistic as possible so it will be versatileenough to encompass the different technique individuals might use to open different styles ofpackaging.

The following sections deal in detail with the requirements for the measuring equipment.Where appropriate, reference should be made to Section 2.6.3 - Experimental design forStage 2.

Two basic instruments needed to be designed, one for pulling open packages and one forpeeling back covers of packages.

2.6.1.2 Peel-back strength measuring instrumentFor peel-back strength the instrument(s) had to allow the following simulated conditions :

Packages with one tab

1. Package on work surface, hand gripping the tab while steadying the package with theother hand

2. Package in hand, gripping the tab with the other hand

Packages with two tabs

3. Package on work surface with each hand gripping one of the two tabs

4. Package hanging down with each hand gripping one of the two tabs

For the first three of these basic grasping and pulling actions the study (ibid) showed thatpeople used one of two techniques when pulling on the tab(s). These were:

• grasping the tab(s) between the thumb and forefinger and pulling the tab(s) while thebase of the gripping hand(s) is clear of the package

• grasping the tab(s) between the thumb and forefinger and pulling the tab(s) whilerotating the wrist(s) i.e. with the hand(s) pressed against the lid of the containers.

The most difficult part of packaging opening is the application of the initial force that breaksthe seal. The equipment therefore needed to measure the initial force that an individual canapply to the tab in the ‘peel-back’ direction.

The measuring equipment therefore needed to allow peel-back actions in any direction i.e.away from the body, towards the body, in a direction to the left or to the right. In allconditions the instrument(s) had to measure maximum force in the direction that the tab is tobe pulled. The instrument also had to allow the participant to position the corner of the unitwith the tab in any position they prefer.

The size of the equipment needed to be approximately 75mm wide to allow the participant tocomfortably pick up and hold the equipment in one hand. The top of the instrument shouldallow the person to press their hand on it for the condition when they rotate the wrist. Theminimum weight should be approximately 100g with a facility to change the weight to 100g,250g and 400g.

2.6.1.3 Tab sizesTab sizes vary greatly between different styles of packaging and on this basis three differenttab sizes were to be investigated in a preliminary study to investigate differences in the forcethat can be applied with the different tab lengths and shapes.

2.6.1.4 Tear strength measuring instrumentFor the tear instrument(s) the following simulated conditions had to be met:

2.6.1.4.1 Opening a large loosely filled bagThe gripping area needed to resemble that found for bag packages that allow the use of powergrips e.g. hand size bags of cereals. The gripping points needed to be very close togetherallowing the hands to be a maximum of 10mm apart and allow the participant the option topull apart whilst pivoting the wrists. The weight of the component should be variable up to 1kg. It should also be possible to rest the instrument on the work surface or above it.

2.6.1.4.2 Opening a medium loosely filled bagThe gripping area needed to resemble that found for actual medium bags that allow the use ofpower grips e.g. small bags filled with beans. The gripping points needed to be very closetogether, allowing the hands to be a maximum of 10mm apart and must allow the participantthe alternative to pull apart whilst pivoting the wrists. The weight of the instrument shouldbe variable up to 1kg and cater for the possibility of being held on the work surface or aboveit.

2.6.1.4.3 Opening a medium fairly tightly filled bagThe gripping area needed to resemble that found for actual bags that allow the use of lateralgrips e.g. tabs that measure 40 x 25 mm. The gripping points needed to be very closetogether allowing the hands to be a maximum of 10mm apart and should allow the participantthe option to pull apart whilst pivoting the wrists. The instrument should weigh up to 500g.

2.6.1.4.4 Opening a small fairly tightly filled bagThe gripping area needed to resemble that found for actual bags that will allow the use ofthree grips; lateral, three finger chuck and finger pinch e.g. gripping areas that measure 30 x20 mm. The gripping points needed to be very close together allowing the hands to be amaximum of 10mm apart and should allow the participant the alternative to pull apart whilstpivoting the wrists. The equipment should weigh 100g.

All instruments needed to provide for the measurement of the initial force that the individualcan apply to the sides of the instrument.

2.6.2 Experimental design for Stage 2

It was envisaged that two main experiments would be undertaken; one would be concernedwith peel-back type packaging, and the other with tear type packaging. The experimentswould need to reflect the type of packages identified as of interest in this stage, the weight ofthe packages, their orientation when opened, and the strategies and techniques employed.

In addition in Stage 2, a preliminary experiment was required to determine the effect of tabshape and size with a view to determining the tab shapes and sizes to be further investigated.Triangular tabs at the corners of packages, for example microwave packages, are commonlyfound. A typical length of triangular tabs is 12 mm that, for many people in this study wasfound to be too small. For the preliminary study, larger sizes i.e. 16 mm and 20 mm deeptriangular shapes were investigated. In addition, rectangular shapes of the same depth wereinvestigated to explore any advantages with this shape.

3. Stage 2. Data collection

3.1 Objectives

To collect data on the strength characteristics of non-disabled and disabled people withregard to peel-back and tear strategies when opening paper and plastic sheet packages.

To define opening strength limits for peel-back and tear packaging for different proportionsof the population.

3.2 Peel-back packaging experiments

3.2.1 Equipment

An instrument was designed to measure participant strength when opening peel back typepackages according to the criteria described in Section 2.6.1.2 (see Figure 1). It comprisedpairs of plastic tabs fixed in an octagonal metal case to simulate the tabs typically found onpeel-back packaging. Inside the metal case were force gauges that were attached to theplastic tabs. By pulling on the tabs the force exerted on the tabs could be presented on aprecision voltmeter once the signal from the force gauges had been suitably processed. Thesize of the metal case was largely dictated by the space required for the force gauges andmeasured 80 mm across opposite sides, and 40 mm in depth. This dictated the minimumweight of the instrument was 296 g. The shape however was such that it could be held in onehand (while pulling on a tab with the other), or placed on a work surface (allowing one or two

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tabs to be pulled while stabilising the unit), or allow the two tabs to be pulled apart separatelywhile the ‘unit was hanging down vertically.

The size and shape of the instrument allowed for variation in how people might hold the unitthereby providing for choice in positioning the unit and hence the tabs.

Figure 1: Instrument used for measuring peel-back strength

3.2.2 Preliminary study

3.2.2.1 Experimental design and procedureThe experimental conditions for the study are shown in Table 3.

Grasping and pulling action type of pull tab size shape of tab condition No.

straight 12mm deep rectangular 1unit on horizontal work-surfacewith one hand gripping upper tabwhile stabilising the unit with theother hand

triangular 2

16mm deep rectangular 3

triangular 4


triangular 6

rotate wrist 12mm deep rectangular 7

triangular 8


triangular 10


triangular 12

Table 3: Experimental conditions for the preliminary study on peel-back strength

The instrumented or unit (see Figure 1) was placed on a horizontal work surface set at 930mm height. For wheelchair users the height setting was 780 mm. The participant wasinstructed to grasp the upper tab of the unit with their preferred hand while stabilising the unitwith the other hand. They were then asked to perform a straight pull using maximum forcebut ensuring their hand was not touching the upper surface of the unit. Participants wereallowed to choose to do this with the unit (and hence the tab) pointing in any direction theyprefer (i.e. towards or away from them, right or left). The pulling task was repeated but withthe wrist rotated while resting against the 'lid' of the container. This procedure was repeated

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using rectangular and triangular shaped tabs 12mm, 16mm and 20mm deep. The rectangularshape had a width of 12mm wide. The depths of the triangular shape determined their width.

16 participants took part in this study, 7 male and 9 female, 7 of whom were over 50 years ofage.

3.2.2.2 ResultsThe results of the preliminary study are shown in Table 4.

tab size(mm)

action mean(N)

standarddeviation (N)

Rectangular 12 peel 21.48 6.82



Rectangular 12 rotate 19.25 2.82



Triangular 12 peel 16.66 4.42



Triangular 12 rotate 13.19 2.79



Table 4: Results of the preliminary study on peel back strength

Significant differences (p<0.05) were only found between exertions for the 12 mm size on thetriangular and rectangular tabs, with forces on the rectangular tab being greater than on thetriangular for both action types. Exertions on the three tab sizes were significantly differentfor all conditions except for between 12 and 16 mm rectangular tabs when a straight peelingaction was used.

The results from the preliminary study showed that the forces exerted for triangular tabs andrectangular tabs were very similar. Since triangular tabs are more commonly found onpackaging, it was decided to use triangular tabs in the main study. The results also show thatthere were differences between tab sizes. However, it was not felt that the differencesbetween the 12 mm and 16 mm, and the 16 mm and 20 mm tabs were sufficiently different towarrant inclusion of all three sizes in the main study. It was therefore decided to include onlythe 12 mm and 20 mm tab sizes in the main study.

3.2.3 Main study

3.2.3.1 ParticipantsThe focus for this study was on people aged 51+ years, with a sample size of 95 (44 male, 51female) divided approximately into 4 equal groups aged 51-60, 61-70, 71-80 and 81+ years.A baseline group was also included of 30 participants aged between 21 and 50 years. Thisincluded 10 persons in each of the three groups 21-30,31-40 and 41-50 years.

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The number of disabled participants was 33. These were chosen to represent as far as waspossible the different levels of dexterity based on severity levels for this impairment asestablished in the UK Government’s survey of disabled persons in Great Britain (Martin et al,1989).

Tables 5 and 6 show the age, sex and numbers of participants involved in the experiments.With the disabled group, the level of dexterity impairment is also shown, based on severitylevels for this impairment as established in the UK Government’s survey of disabled personsin Great Britain (Martin et al, 1989).

Age yrs male female total

21 - 50 15 15 30

51-60 12 11 23

61-70 11 15 26

71-80 16 16 32

81+ 5 9 14

Total 44 51 95

Table 5: Non disabled participants

dexterity severity male female total

10.5 3 4 7

9.5 0 1 1

8 1 2 3

7 2 4 6

6.5 1 4 5

5.5 1 5 6

4 1 0 1

3 0 0 0

2 2 2 4

1.5 0 0 0

0.5 0 0 0

Total 11 22 33

Table 6: Disabled participants

3.2.3.2 ProcedureThe procedure adopted for the measurements was the same as that used for the preliminarystudy (see Section 3.2.2.1 above).

The four basic grasping and pulling conditions are illustrated:

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Figure 2: Unit on work surface, hand grippingupper tab while steadying the unit withthe other hand.

Figure 3: Unit on work surface witheach hand gripping one of thetwo tabs

Figure 4: Unit in hand, gripping the tab with theother hand.

Figure 5: Unit hanging down with eachhand gripping one of the twotabs.

Participants were allowed to choose to have the container (and hence the tab) pointing in anydirection they preferred (i.e. towards or away from them, right or left).

Participants were asked to grip either the tab or tabs and apply maximum opposing pullingforce. For three of the conditions (illustrated in Figures 2, 3 and 4 above), participants wereasked to use each of the following two techniques when pulling on the tab(s):

• grasping the tab(s) between the thumb and forefinger and pulling the tab(s) while thebase of the gripping hand(s) is clear of the unit

• grasping the tab(s) between the thumb and forefinger and pulling the tab(s) whilerotating the wrist(s) i.e. with the hand(s) pressed against the lid of the containers.

For the other condition (Figure 5 above), only the first of these grasping actions wasemployed. These actions were performed with two triangular tab lengths of 12 and 20 mm.

Anthropometric measures were also taken for each participant including stature, weight andknuckle width and thumb breadth.

3.2.3.3 Experimental designBased on the earlier analysis of peel-back type packaging, it was originally envisaged thatweights varying from 100 to 400g would be simulated. The minimum weight achievablehowever, in the design of the measuring unit was, as previously stated, 296g. It was therefore

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decided not to attempt any variation in the simulated weight in the experiment. Similarly theshape of the unit was largely dictated by the components and circuitry inside the casing.However it was felt that the shape would not significantly affect hand and finger posture whenholding the simulated package or influence the strength that could be applied under differentconditions. Table 5 shows the experimental design for the main study on peel back strength.

Grasping and pulling action tab size type of pull condition No.

12 mm

20 mm

straight 1

2

unit on horizontal work-surface witheach hand gripping one of the two tabshorizontally

12 mm

20 mm

rotate wrist 3

4

12 mm

20 mm

straight 5

6

unit on horizontal work-surface withone hand gripping upper tab whilestabilising the unit with the other hand(weight is irrelevant because it ismeant to be held on worktop)

12 mm

20 mm

rotate wrist 7

8

12 mm

20 mm

straight 9

10

holding the unit in one hand whilegripping the upper tab in the other

12 mm

20 mm

rotate wrist 11

12

unit vertical (i.e. hanging down) witheach hand gripping one of the two tabs

12 mm

20 mm

straight 13

14

Table 7: Experimental design for peel-back measurements

3.2.4 Results

The tabulated results for the each of the above conditions in the form of descriptive statisticsare shown in the Appendix 3. Results are given for each of the age groups 51-60, 61-70, 71-80 and 81+ years and for the base-line age group, 21 to 50 years. The results for the disabledgroup are also given.

The tabulated results in the form of descriptive statistics are shown in Section 1.1 ofAppendix 4.

3.2.4.1 Proportion of people capable of exerting different levels of peel-back forceFrom the results calculations can be made as to the proportions of people who are able toexert different forces for each of the different conditions. The graphs in Sections 3.2.4.1.1 to3.2.4.1.14 below the percentages of people capable of exerting different amounts of force foreach grasping and pulling action, for each of the two sizes of tab and for each pullingtechnique.

3.2.4.1.1 Two tabs - unit on worktop straight pull 12mm [each hand grasping a tab and exerting astraight peel-back pull with a 12 mm tab (Condition 1)]

Force (N) Disabled (%) Non disabled (%)

0 100 100

5 93 98

10 52 88

15 31 68

20 10 44

25 0 24

30 0 12

35 0 6

40 0 3

0%

10%

20%30%

40%

50%

60%

70%80%

90%

100%

0 5 10 15 20 25 30 35 40 45

Force (N)

% a

ble

to

exe

rt f

orc

e

non-disabled aged 51+ disabled 45 0 1

3.2.4.1.2 Two tabs - unit on worktop straight pull 20mm [each hand grasping a tab and exerting astraight peel-back pull with a 20 mm tab (Condition 2)]


0 100 100

5 100 100

10 93 94

15 59 78

20 38 61

25 28 43

30 10 28

35 0 19

40 0 11

45 0 4

50 0 2

0%

20%

40%

60%

80%

100%

0 5 10 15 20 25 30 35 40 45

Force (N)

% a

ble

to

exe

rt f

orc

e

non-disabled aged 51+ disabled

55 0 2

3.2.4.1.3 Two tabs - unit on worktop rotating pull 12mm [each hand grasping a tab and exerting a peel-back pull with wrist rotating with a 12 mm tab (Condition 3)]


0 100 100

5 93 100

10 71 92

15 36 72

20 21 51

25 7 29

30 0 14

35 0 4

40 0 2

0%

20%

40%

60%

80%

100%

0 5 10 15 20 25 30 35 40 45

Force (N)

% a

ble

to

exe

rt f

orc

e


3.2.4.1.4 Two tabs - unit on worktop rotating pull 20mm [each hand grasping a tab and exerting a peel-back pull with wrist rotating with a 20 mm tab (Condition 4)]


0 100 100

5 100 99

10 96 96

15 75 83

20 50 68

25 29 55

30 14 39

35 11 26

40 4 18

45 0 5

50 0 4

0%10%20%30%40%50%60%70%80%90%

100%

0 5 10 15 20 25 30 35 40 45

Force (N)

% a

ble

to

exe

rt f

orc

e


55 0 2

3.2.4.1.5 One tab - unit on worktop straight pull 12mm [one hand stabilising the unit and the other grasping the taband exerting a straight peel-back pull with a 12 mm tab (Condition 5)]


0 100 100

5 86 100

10 69 96

15 48 83

20 24 61

25 17 41

30 10 26

35 3 18

40 0 7

45 0 2

50 0 1

0%

20%

40%

60%

80%

100%

0 5 10 15 20 25 30 35 40 45

Force (N)

% a

ble

to

exe

rt f

orc

e


55 0 1

3.2.4.1.6 One tab - unit on worktop straight pull 20mm [one hand stabilising the unit and the other grasping thetab and exerting a straight peel-back pull with a 20 mm tab (Condition 6)]


0 100 100

5 100 100

10 83 97

15 73 820

20 47 72

25 27 59

30 10 47

35 10 36

40 7 25

45 3 21

50 3 13

0%

20%

40%

60%

80%

100%

0 5 10 15 20 25 30 35 40 45

Force (N)

% a

ble

to

exe

rt f

orc

e


55 3 7

3.2.4.1.7 One tab - unit on worktop rotating pull 12mm [one hand stabilising the unit and the other grasping thetab and exerting a peel-back pull with wrist rotating with a 12 mm tab (Condition 7)]


0 100 100

5 97 100

10 70 93

15 37 76

20 27 59

25 10 34

30 10 21

35 3 13

40 0 5

0%

20%

40%

60%

80%

100%

0 5 10 15 20 25 30 35 40 45

Force (N)

% a

ble

to

exe

rt f

orc

e


45 0 2

3.2.4.1.8 One tab - unit on worktop rotating pull 20mm [one hand stabilising the unit and the other grasping thetab and exerting a peel-back pull with wrist rotating with a 20 mm tab (Condition 8)]


0 100 100

5 100 100

10 90 97

15 71 87

20 55 72

25 32 64

30 23 52

35 10 39

40 3 24

45 0 16

50 0 12

0%

20%

40%

60%

80%

100%

0 5 10 15 20 25 30 35 40 45

Force (N)

% a

ble

to

exe

rt f

orc

e


55 0 6

3.2.4.1.9 One tab - unit in hand straight pull 12mm [one hand holding unit with the other grasping the tab andexerting a straight peel-back pull with a 12 mm tab (Condition 9)]


0 100 100

5 85 100

10 70 95

15 45 82

20 18 62

25 15 40

30 6 24

35 0 15

40 0 9

45 0 4

0%

20%

40%60%

80%

100%

0 5 10 15 20 25 30 35 40 45

Force (N)

% a

ble

to

exe

rt


50 0 1

3.2.4.1.10One tab - unit in hand straight pull 20mm [one hand holding unit with the other grasping the tab andexerting a straight peel-back pull with a 20 mm tab (Condition 10)]


0 100 100

5 94 100

10 85 99

15 70 91

20 52 69

25 27 57

30 9 43

35 6 37

40 0 21

45 0 16

50 0 14

0%

20%

40%

60%

80%

100%

0 5 10 15 20 25 30 35 40 45

Force (N)

% a

ble

to

exe

rt


55 0 11

3.2.4.1.11One tab - unit in hand rotating pull 12mm [one hand holding unit with the other grasping the tab andexerting a peel-back pull with wrist rotating with a 12 mm tab (Condition 11)]


0 100 100

5 84 100

10 66 95

15 47 75

20 19 54

25 9 37

30 6 24

35 0 12

40 0 5

45 0 3

0%

20%

40%

60%

80%

100%

0 5 10 15 20 25 30 35 40 45

Force (N)

% a

ble

to

exe

rt


3.2.4.1.12One tab - unit in hand rotating pull 20mm [one hand holding unit with the other grasping the tab andexerting a peel-back pull with wrist rotating with a 20 mm tab (Condition 12)]


0 100 100

5 100 100

10 88 97

15 63 85

20 53 78

25 31 64

30 16 51

35 6 41

40 6 26

45 3 18

50 3 11

55 0 10

0%

20%

40%

60%

80%

100%

0 5 10 15 20 25 30 35 40 45

Force (N)

% a

ble

to

exe

rt


3.2.4.1.13Two tabs - unit hanging down straight pull 12mm [unit held vertically with each hand grasping a taband exerting a straight peel-back pull with a 12 mm tab (Condition 13)]


0 100 100

5 83 100

10 55 95

15 31 76

20 10 46

25 3 23

30 3 9

35 0 3

40 0 2

0%

20%

40%

60%

80%

100%

0 5 10 15 20 25 30 35 40 45

Force (N)

% a

ble

to

exe

rt f

orc

e


45 0 1

3.2.4.1.14Two tabs - unit hanging down straight pull 20mm [unit held vertically with each hand grasping a taband exerting a straight peel-back pull with a 20 mm tab (Condition 14)]


0 100 100

5 100 99

10 87 99

15 60 83

20 43 61

25 20 45

30 10 31

35 3 17

40 3 5

0%

20%

40%

60%

80%

100%

0 5 10 15 20 25 30 35 40 45

Force (N)

% a

ble

to

exe

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orc

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45 0 2

3.2.5 Analysis

3.2.5.1 Comparison of over 50 year groups with 21-50 age base-line groupA general decrease in peel strength with age is evident. The majority of statistically significantdifferences are between the 21-50 age group and the 71-80 and 81+ groups, with no statisticallysignificant differences between the 21-50 and 51-60 group, and only three conditions showingstatistically significant differences between the 21-50 and 61-70 groups (Conditions 4, 11 and 13).Although strength declines with age, it is only after age 71 that (statistically) significant differenceswhen compared to the under 50 year group, become common (see Appendix 4, Section 1.2.4.2).

3.2.5.2 Effect of unit positionTwo conditions gave the greatest strength exertions. These were firstly with the unit on the worksurface and the free hand holding the unit steady, and secondly with the unit in the hand. Equalforce exertions were achieved for both positions. This was true for both straight pull and rotationtechniques on both sizes of tab (see Appendix 4, Section 1.1.2).

The result can be explained by the fact that the other two unit positions involved the unit beingsteadied by gripping the second tab, which resulted in participants only being able to apply a smallergripping force than when holding the whole unit in the hand.

3.2.5.3 Effect of tab sizeFor the 50 years and older groups exertions on the 20 mm tab size were significantly larger than onthe 12 mm tab for both straight pull and rotation techniques (regardless of how the unit was held)(see Appendix 4, Section 1.1.3). The smallest difference (approximately 4 N) was found with theunit vertical i.e. hanging vertically down. The greatest difference (approximately 9 N) was with theunit in the hand with a rotating action.

With the disabled group, the 20mm tab produced an average increase of 6.53N in the forceparticipants could exert compared with the 12mm tabs. The difference in this increase for eachcondition ranged from 5.06N to 7.82N. In summary this meant that on average there was nearly a50% increase on the force that could be exerted when using the 20 mm tab compared with the 12 mmtab. Overall, there was very little difference between the results obtained for each of the differentpulling techniques despite some variability. A very slight increase in force, if any, could be exertedwhen rotating the wrist than with the straight pull but this was only applicable for the 20mm tabconditions where it provided on average a 2N increase in force.

3.2.5.4 Effect of techniqueThe rotation technique was found to result in greater force exertion on all conditions involving the 20mm tab, while the straight pull technique produced greater force on the 12 mm tab. All differencesbetween the straight pull and the rotation techniques on 12 mm tabs were statistically significant,while only one difference on the 20 mm tabs was significant (see Appendix 4, Section 1.1.1).

3.2.5.5 Effect of sexMales were found to be stronger than females at all ages although the differences were not alwaysstatistically significant (see Appendix 4, Section 1.1.4).

3.2.5.6 Effect of disabilityTo assess the effect of disability it is necessary to compare the results (across all age groups) for thedisabled group of participants with those in the non-disabled.

For the 12mm size tabs, the non-disabled participants on average showed an 8.27N increase over thedisabled participants for each condition and technique. This difference ranged from 7.02N to 9.43N.This was on average a 60% increase in strength applied by non-disabled participants over disabledparticipants across all of the conditions.

For the 20mm size tabs the non-disabled participants on average showed an 8.43N increase over thedisabled participants using each posture and technique. This difference ranged from 5.62N to11.44N. This was on average a 41% increase in strength for non-disabled participants over disabledparticipants across all of the conditions.

This would imply that the increase in tab size had a more positive effect on the performance of thedisabled participants than non-disabled participants. In fact the forces produced by the disabledparticipants using the 20mm tab were very similar (but marginally lower) than the forces producedby the non-disabled participants using the 12mm tab.

Participants’ force capability when using different techniques and postures followed a very similarpattern for both the disabled and non-disabled. Implying that there was no particular technique orposture that improved or impaired the performance of the disabled participants in relation to the non-disabled participants.

These results are illustrated in Table 7 and Figures 6 and 7.

12 mm tab 20mm tab

disabled non-disabled disabled non-disabled

two tabs worktop straight 11.52 19.62 18.79 25.02

two tabs worktop rotate 14.08 21.10 21.90 27.52

two tabs hanging straight 12.22 20.24 18.71 24.45

one tab worktop straight 15.35 24.69 20.91 30.86

one tab worktop rotate 15.11 22.61 22.22 31.16

one tab hand straight 14.60 24.03 19.66 31.10

one tab hand rotate 14.32 22.83 20.71 31.76

Table 7: Average strength that could be applied with 12 and 20 mm tab lengths for disabled andnon-disabled groups of participants

two

tabs

wor

ktop

stra

...

two

tabs

wor

ktop

rota

te

two

tabs

han

ging

str

a...

one

tab

wor

ktop

stra

ight

one

tab

wor

ktop

rota

te

one

tab

hand

stra

ight

one

tab

hand

rot

ate

05

10152025

Str

en

gth

(N

)

Mean maximum strength exerted for different techniques for disabled and non-disabled for the

12mm tab size

disabled

non-disabled

two

tabs

wor

k...

two

tabs

han

gi..

one

tab

wor

kto.

..on

e ta

b ha

nd r.

..0

10

20

30

Str

en

gth

(N

)Mean maximum strength exerted for

different techniques for disabled and non-disabled for the 20mm tab size

disabled

non-disabled

Figure 6: Mean maximum strengths exerted bydisabled and non-disabled participants for 12mm tab size for different opening techniques.

Figure 7: Mean maximum strengths exerted by disabledand non-disabled participants for 20 mm tab sizefor different opening techniques

3.2.5.7 Proportion of people capable of exerting different levels of peel-back forceThe graphs in Sections 3.2.4.1.1 to 3.2.4.1.1.14 show the percentages of people capable of exertingdifferent amounts of force on the two tabs and for each technique. It is obvious from these results thatthe non-disabled participants performed much better than the disabled participants across all of theconditions. Where one level of force would be acceptable for the non-disabled population (i.e. for95% of that population), this level would not meet the needs of the majority of the disabledpopulation. For 12mm tabs a force of 5N, and for 20mm tabs a force of 10N could be managed byover 80% of the participants in all conditions by both disabled and non-disabled participants.However, increasing the force more than this (even by only 5N) produced a drastic decrease in thepercentage of disabled participants capable of exerting that force.

For example, in the condition where the participant grasps two tabs and allows the unit to hang downwhilst pulling the tabs apart; 83% and 100% of disabled and non-disabled participants respectivelycan exert 5N of force. However, increase this to 10N and 95% of non-disabled participants are stillcapable but the percentage of disabled participants has fallen to 55%.

3.2.5.8 Correlations of hand anthropometry and strengthCoefficients of correlation between knuckle width and thumb pad width and all peel strengthconditions for the non-disabled and disabled participant groups were calculated to assess therelationship between hand size and force exertion. The largest observed R value for both groups wasfor knuckle width with the unit on the work surface, both tabs being held with a rotation action pullon the 20 mm tab (R= 0.448), giving an R_ value of 0.20. This means that a maximum of only 20%of the variability in peel force exertion can be accounted for by knuckle size. A similar result wasobtained with the disabled participant group with the unit held in one hand while pulling the 20 mmtab using hand rotation (R=0.487) giving an R_ value of 0.24.

The largest observed R value for thumb pad width for the non-disabled participant group was withthe unit in the hand, pulling on a 12 mm tab (R= 0.465), giving an R_ value of 0.22. This means thatonly a maximum of 22% of the variability in force exertion can be accounted for by thumb padbreadth. The largest R value for the disabled participant group for thumb pad width was again withthe unit held in one hand while pulling the 20 mm tab using hand rotation (R=0.363, R_=0.13)

3.2.5.9 Addendum to peel-back experimentWork on skin friction by Bobjer (1993) has demonstrated that friction between the skin and manymaterials can be improved if a texture is introduced on the surface of the material in which the skin isin contact. As a final contribution to the peel-back experimentation a small study was conducted atthe end the main studies to investigate the effect of tab texture. Six participants were tested using12mm triangular tabs, one of which was smooth whilst the other had raised 1 mm strips gluedhorizontally across its surface. Each participant used the straight pull only on each tab.

Adding ridges to tabs was found to significantly increase the force people could exert as shown inTable 8 (t = 2.36, d.f = 7, p<0.05).

Tab type Mean sdSmooth 18.85 8.45Textured 25.23 8.26

ttestt df sig

2.36 5 0.001

Table 8: Means and sd’s for forces that could be applied to a 12 mm tab with smooth and textured surfaces and analysisof variance

The result of this small experiment shows that there was approximately a 40 % increase in strengththat could be applied. It would suggest that if manufacturers were to apply a texture to the tabsurface this would significantly improve the amount of strength that could be applied. In order toquantify the benefit more precisely and investigate different type of textures, more comprehensiveresearch would need to be undertaken.

3.2.6 Concluding remarks from peel-back experiment

From qualitative data collected during the study it is possible to identify a number of causes for thelower performance of the disabled group compared to the non-disabled.

The smaller tab exacerbated problems for the disabled participants. This was because they oftenfound it more difficult to get a comfortable and strong grip (as in the case of participants witharthritis), and also more difficult to co-ordinate (as in the case of participants with multiple sclerosisand ataxia) gripping the tab.

Disabled participants had much more control when holding the unit near to their body, and in somecases they could only complete the task of pulling the tabs when they could adopt this posture, whichmeant that they found it very difficult or impossible when they had to hold the unit down on theworktop. They also found it more difficult when they were required to rotate their wrist as this was amore dexterous technique requiring a combination of actions.

A number of participants had to adopt a compensatory technique, as do many disabled people whencompleting such tasks. These involved holding the tab in unusual ways (e.g. with the thumb on topand the fingers on the bottom) and pulling in unusual directions. In some cases the participants wereweakened in one hand (due to a stroke for example) and could therefore only complete the one tabconditions as it was impossible for them to grip two tabs. If they had no use at all in their weakerhand they could only manage two of the conditions, which allowed them to compensate using onlyone hand. With the unit on the work surface they could grip the tab and pull by rotating the wrist andpressing their hand down onto the top of the unit. Optionally they could use a similar technique withthe unit held between their knees.

With respect to the non-disabled participants males were stronger than females for all of the tasksinvolving peel back. There was also a general decrease in maximum strength with age. Both thedisabled and non-disabled groups showed an increase in force exerted with the 20mm tabs over the12mm tabs regardless of technique or posture. Despite some variability posture did not appear to bean important factor relating to peel strength. Non-disabled participants performed significantly betterwith the straight pull with the 12mm tab than when rotating the hand. In contrast the disabledparticipants performed slightly better when rotating the wrist with the 20mm tab than using a straightpull.

The findings indicate that for peel-back strength in general, no more than approximately one-quarterof the variability in force exertion can be accounted for by differences in hand anthropometry.

The disabled sample included in this report was relatively small. While the results from this groupcannot be considered as definitive, they do reveal the limited strength disabled people can applywhen opening paper and plastic packaging. Previous research has revealed that a large number ofdisabled people have difficulties with such packaging (DTI, 2000). If they are to be accommodateddesigners need to seriously consider their capabilities.

The non-disabled group included in this study consisted of elderly participants aged 51 years andover because it was felt that if their needs were met then the needs of younger adults would also beaccommodated therefore accommodating a vast majority of the non-disabled population.

All of the unit used in this study was designed to simulate behaviour actually used when openingpackaging. The results obtained should therefore be considered representative of the needs ofconsumers when opening actual packaging.

3.2.7 Implications for packaging design

Previous DTI commissioned research has demonstrated the considerable problems disabled peopleand older people have when attempting to open different types of packaging (DTI, 2000). One of themost common reasons for failure to open packaging was the amount of force needed. In order toimprove this situation and reduce the reliance on the use of tools such as scissors or knives (which itis known result in injuries), the strength capabilities of disabled people and people aged 51 years andover, need to be taken into account.

The conclusions of this research demonstrate that tab sizes on peel-back type packaging should be aslarge as possible and at least 20 mm in length. Regardless of the technique used to pull on the tabs,larger tabs result in greater force exertion, and disabled persons also have difficulty gripping smallertabs. As the force required to open peel-back packaging increases the proportion of disabled personscapable of exerting the force decreases, and so the provision of larger tabs may be crucial in ensuringdisabled persons are able to cope with modern packaging.

In determining acceptable forces for opening peel-back packages, designers need to consider theproportions of disabled people and people over 50 years of age that are accommodated as shown inthis report. Clearly the minimum pull force required to open a peel-back package should be as low asis possible consistent with the need to maintain the integrity of the contents under the differentconditions the package is likely to be exposed to. However designers will need to weigh theproblems that might arise when attempting to reduce forces against the proportions of people whomight be accommodated with such reductions.

Other techniques aimed at increasing the force that can be applied should also be considered. Forexample increasing the pulling force by choosing a tab material that has high frictional propertieswhen in contact the skin surface might be one such technique.

3.3 Tear packaging experiments

3.3.1 Measuring equipment for tear type packaging

Measuring instruments were design and developed according to the criteria set out in Section 2.6.1.4.The basic design comprised two metal bars to which different bags could be attached on either side(see Figure 8 below). The bars pivoted onto a load cell at one end. The resultant applied force wasregistered on a precision voltmeter once the signal from the load cell had been suitably processed.The combined instrument measured 138 mm (length), by 19 mm (height) by 14 mm (thickness).Three different sized bags were made to attach to the bars, which differed in the amount of materialavailable to grip (largely dictated by the amount of protrusion from each side of the metal bars) andin the weight attached, as follows :

bag weight protrusion

Small 148g 20 mm

Medium 500g 40 mm

Large 1000g 60 mmTable 8: Bag types, weights and amount of protrusion

The material used for the simulated bag was a plastic material typically used for many types ofpackaging, selected primarily for its strength and durability. Material with a higher skin interface

Figure 8: Equipment to measure tear strength with and without a bag attached.

3.3.2 Preliminary study

It was considered important to first test whether the weight of the bag would have any significanteffect on people’s strength. Six participants each attempted a straight pull using both a lateral gripand a power grip. This was completed using the medium bag (with a grip area of 40mm) weighing500g and 1kg. The results are shown in Table 12.

grip weight mMean sd

Lateral 500g 54.36 17.23

1kg 59.43 18.45

Power 500g 80.83 49.87

1kg 84.63 50.40Table 10: Results of the preliminary study on tear strength

Although the amount of strength that participants could apply varied only a small amount withdiffering weights (5N difference out of 55N for the lateral grip, and less than 4N out of 80N for thepower grip), it was nevertheless concluded that different weights would be used to simulate differentsize packages in the main study.

3.3.3 Main study

3.3.3.1 ParticipantsSeventy-five non-disabled participants (37 male, 38 female) and 31 disabled participants (6wheelchair users) took part in the study, subject numbers are shown in Tables 13 and 14. A baselinegroup was also included of 30 participants aged between 21 and 50 years. This included 10 personsin each of the three groups 21-30,31-40 and 41-50 years.

Tables 11 and 12 show the age, sex and numbers of participants involved in the experiments. Withthe disabled group, the level of dexterity impairment is also shown, based on severity levels for thisimpairment as established in the UK Government’s survey of disabled persons in Great Britain(Martin et al, 1989).

age yrs male female total

21-50 15 15 30

51-60 7 11 18

61-70 9 10 19

71-80 14 12 26

81+ 7 5 12

Total 37 38 75

Table 11: Non-disabled participant numbers

dexterity male female total

10.5 3 4 7

9.5 0 1 1

8 1 1 2

7 1 3 4

6.5 2 4 6

5.5 1 4 5

4 1 0 1

3 0 0 0

2 2 1 3

1.5 1 1 2

0.5 0 0 0

Total 12 19 31Table 12: Disabled participant numbers

3.3.3.2 ProcedureThe procedure adopted for the measurements was for the participant to stand (ambulantpersons) or sit (wheelchair users) adopting an otherwise free posture. The unit was placed ona work surface set at 930 mm height. For wheelchair users the height setting was 780 mm.

The participant was asked to grip either side of the bag with each hand and apply maximumopposing pulling force using two techniques:

• with the hands separated and exerting a straight two handed pull

• a two handed pull with both hands pivoted at the wrist

These actions were performed with specific grips for different size bags as follows:

• large bag (60 mm graspable) - power grip

• medium sized bag (40 mm graspable) - power and lateral grip

• small bag (20 mm graspable) - lateral, three fingered chuck and finger pinch grip

3.3.3.3 Experimental designThe table below shows the experimental design for the study on tear strength.

characteristics of product grip type pull type weight condition no.

power straight 1kg 1Large bag (60 mm graspablearea) power wrists pivoting 1kg 2

power straight 500g 3

power wrists pivoting 500g 4

lateral straight 500g 5

Medium bag (40 mmgraspable area)

lateral wrists pivoting 500g 6

lateral straight 118g 7

lateral wrists pivoting 118g 8

three finger chuck straight 118g 9

three finger chuck wrists pivoting 118g 10

pinch straight 118g 11

Small bag (20 mm graspablearea)

pinch wrists pivoting 118g 12

Table 13: Experimental design for peel-back measurements.

Anthropometric measures were taken for each participant, including stature, weight, knucklewidth and thumb width.

The different simulated conditions for opening packages are shown in the figures below:

Small bag with 20 mm graspable area simulating a small package e.g. a packets of nuts.

Figure 9: Grips for small bag: From top to bottom the grips are pinch, 3 finger chuck, and lateral. Pictures onthe left are straight pulls, pictures on the right are pulls with wrists pivoting (Conditions 7 to 12).

Medium bag with 40 mm graspable area simulating a medium size package e.g. packets of driedfruit.

Figure 10: Grips for medium bag: From top to bottom the grips are lateral and power. Pictures on the left arestraight pulls, pictures on the right are pulls with wrists pivoting (Conditions 3 to 6).

Large bag with 60 mm graspable area simulating a large size packages e.g. packets of cereals.

Figure 11: Grips for large bag: Pictures on the left are straight pulls, pictures on the right are pulls with wristspivoting. (Conditions 1 and 2)

3.3.4 Results

The tabulated results for the each of the above conditions in the form of descriptive statisticsare shown in the Appendix 3. Results are given for each of the age groups 51-60, 61-70, 71-80 and 81+ years and for the base-line age group, 21 to 50 years. The results for the disabledgroup are also given.

Anthropometric variables for all subjects (stature, weight, and knuckle breadth and thumbbreadth) can be found in Section 1.3 of Appendix 4.

3.3.4.1 Proportion of people capable of exerting different levels of tear forceFrom the results calculations can be made as to the proportions of people who are able toexert different forces for each of the different conditions. The graphs in Sections 3.3.1 to3.3.12 below the percentages of people capable of exerting different amounts of force foreach size of bag, each type of grip and for each pulling technique.

3.3.4.1.1 Large bag (60 mm) using power grip and exerting a straight pull (Condition 1).


0 100 100

20 67 97

40 44 88

60 19 68

80 7 55

100 4 39

120 0 24

140 0 13

160 0 7

180 0 3

0%

20%

40%

60%

80%

100%

0 10 20 30 40 50 60 70 80 90

Force (N)

% a

ble

to

exe

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200 0 1

3.3.4.1.2 Large bag (60 mm) using power grip and exerting a pull with wrists pivoting (Condition 2).


0 100 100

20 52 85

40 19 61

60 4 28

80 4 8

100 0 30%

20%

40%

60%

80%

100%

0 10 20 30 40 50 60 70 80 90

Force (N)

% a

ble

to

exe

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3.3.4.1.3 Medium (40 mm) using power grip and exerting a straight pull (Condition 3).


0 100 100

20 61 100

40 25 83

60 7 56

80 7 32

100 0 16

120 0 7

140 0 1

0%

20%

40%

60%

80%

100%

0 10 20 30 40 50 60 70 80 90

Force (N)

% a

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to

exe

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3.3.4.1.4 Medium (40 mm) using power grip and exerting a pull with wrists pivoting (Condition 4).


0 100 100

20 36 92

40 14 64

60 4 36

80 0 11

100 0 4

120 0 10%

20%

40%

60%

80%

100%

0 10 20 30 40 50 60 70 80 90

Force (N)

% a

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to

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3.3.4.1.5 Medium (40 mm) using lateral grip and exerting a straight pull (Condition 5).


0 100 100

20 42 96

40 4 49

60 0 15

80 0 5

100 0 1

0%

20%

40%

60%

80%

100%

0 10 20 30 40 50 60 70 80 90

Force (N)

% a

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to

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3.3.4.1.6 Medium (40 mm) using lateral grip and exerting a pull with wrists pivoting (Condition 6).


0 100 100

10 72 99

20 32 77

30 8 47

40 0 29

50 0 20

60 0 8

70 0 3

80 0 1

0%

20%

40%

60%

80%

100%

0 5 10 15 20 25 30 35 40 45

Force (N)

% a

ble

to

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3.3.4.1.7 Small (20 mm) using lateral grip and exerting a straight pull (Condition 7).


0 100 100

10 76 100

20 20 68

30 4 20

40 0 30%

20%

40%

60%

80%

100%

0 5 10 15 20 25 30 35 40 45

Force (N)

% a

ble

to

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3.3.4.1.8 Small (20 mm) using lateral grip and exerting a pull with wrists pivoting (Condition 8).


0 100 100

5 81 100

10 46 85

15 19 69

20 4 45

25 4 16

30 0 5

35 0 3

0%

20%

40%

60%

80%

100%

0 5 10 15 20 25 30 35 40 45

Force (N)

% a

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40 0 1

3.3.4.1.9 Small (20 mm) using chuck grip and exerting a straight pull (Condition 9).


0 100 100

4 100 100

8 61 100

12 39 92

16 22 69

20 13 51

24 0 29

28 0 13

32 0 5

0%

20%

40%

60%

80%

100%

0 2 4 6 8 10 12 14 16 18

Force (N)

% a

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36 0 1

3.3.4.1.10Small (20 mm) using chuck grip and exerting a pull with wrists pivoting (Condition 10).


0 100 100

4 90 100

8 43 95

12 19 65

16 5 47

20 5 25

24 0 3

28 0 1

32 0 1

0%

20%

40%

60%

80%

100%

0 2 4 6 8 10 12 14 16 18

Force (N)

% a

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3.3.4.1.11Small (20 mm) using pinch grip and exerting a straight pull (Condition 11).


0 100 100

4 96 100

8 50 93

12 25 81

16 8 61

20 8 44

24 0 21

28 0 8

32 0 4

0%

20%

40%

60%

80%

100%

0 2 4 6 8 10 12 14 16 18

Force (N)

% a

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36 0 1

3.3.4.1.12 Small (20 mm) using pinch grip and exerting a pull with wrists pivoting (Condition 12).


0 100 100

4 92 100

8 38 88

12 13 67

16 4 41

20 4 17

24 0 7

28 0 4

32 0 4

36 0 3

0%

20%

40%

60%

80%

100%

0 2 4 6 8 10 12 14 16 18

Force (N)

% a

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40 0 1

3.3.5 Analysis

3.3.5.1 Comparison of over 50 year groups with 21-50 age base-line groupA general decrease in tear strength with increasing age is evident. Some differences howevercan be found between the different age groups for different conditions. These differences areshown below:

Comparing the 21-50 and 81+ age groups, statistically significant differences werefound in the strength that could be applied for all conditions.

Comparing the 21-50 and 71-80 age groups, only Condition 6 (laterally gripping amedium sized bag while using a wrist pivoting action) did not give statisticallysignificant differences.

For age groups 21-50 and 61-70 the only statistically significant differences occurredwith exertions on the small bag. These occurred in all conditions with the exceptionof Condition 12 (using a pinch grip with pivoting action).

Comparing ages 21-50 and 51-60 the only statistically significant difference was withthe medium bag using a lateral grasp with a straight pull action (Condition 5).

Overall, a similar picture to peel strength emerges, in that most (statistically)significant differences occur between people aged over 70 years and people aged 50years and under.

3.3.5.2 Effect of bag sizeClearly increasing bag size (thereby increasing graspable area) gave markedly higher meanvalues for the strengths that could be applied. However the scale of difference between thelarge and small bag was not as great for disabled participants as for non-disabled participants.For all bag sizes the simple pull technique gave higher values than for the wrist pivoting.

3.3.5.3 Effect of techniqueFor all experimental conditions (e.g. type of grip, bag size/weight) tear strength exerted usinga straight pull was statistically significantly larger than strength exerted with the wristspivoting (see Appendix 4, Section 1.2).

3.3.5.4 Effect of gripA general increase in force is evident with increase in type of grip i.e. from pinch grip topower grip. Only one pairing (chuck grip with wrist pivoting vs. pinch grip with wristpivoting with the small bag) did not show a statistically significant difference between griptypes (see Appendix 4, Section 1.2.2).

Effect of genderMales were found to be stronger than females at all ages, although the differences were notalways statistically significant (see Appendix 4, Section 1.2.3).

3.3.5.5 Effect of disabilityThe effect of disability is largely that of the amount of force that could be applied. Non-disabled persons were able to apply forces 3 to 4 times that of non-disabled participants (seefollowing section).

3.3.5.6 Proportion of people capable of exerting different levels of tear forceThe graphs in Sections 3.3.4.1.1 to 3.3.4.1.12 show the percentages of people capable ofexerting different amounts of force for different size bags, grips and techniques. It isapparent from these results that the non-disabled participants performed much better than thedisabled participants across all of the conditions. Where one level of force would beacceptable for the non-disabled population (i.e. for 95% of that population), this level wouldnot meet the needs of the majority of the disabled population. Any increase in forcedecreases the percentage of disabled people compared to non-disabled people able to exertsuch a force. For example, in the condition of a straight pull with a power grip on the largebag, 100 % of non-disabled and 80 % of disabled participants can exert a force of 10 N. Anincrease of 10 N to 20 N reduces these figures to 97 % of non-disabled, and 67 % of disabled.At a force of 40 N the non-disabled percentage has only fallen by 9% to 88 %, while thedisabled population has fallen by 23 % to 44 %.

3.3.5.6 Correlations of hand anthropometry and strengthCoefficients of correlation were also calculated between knuckle width and thumb pad widthand all tear strength conditions for the non-disabled and disabled participant groups to assessthe relationship between hand size and force exertion. The greatest value of R for knucklewidth was for a straight pull on the medium bag with a power grip (R= 0.510), giving an R_value of 0.26. This means that a maximum of only 26% of the variability in tear forceexertion can be accounted for by knuckle width size. For the disabled participant groupgenerally higher R values were found. The greatest R value occurred with was for themedium size bag with the power grip (R=0.691) giving a R_ value of 0.47.

The largest observed value of R for thumb pad breadth was for a rotating pull on the smallbag with a chuck grip (R= 0.467), giving an R_ value of 0.22. This means that a maximum ofonly 22% of the variability in tear force exertion can be accounted for by thumb pad breadthsize. For the disabled participant group the greatest R value again occurred with the mediumsize bag with the power grip (R=0.475) giving a R_ value of 0.23.

3.3.6 Concluding remarks from tear experiments

In all cases the straight pull produced greater force than when pivoting the wrists. Onaverage this increase was 5.38N. For the 51 years and over groups this difference varied agreat deal over the different conditions, ranging from 4.39 (with the small size bag) to 39.61N(large size bag). At worst it provided a 20% increase in force and at best a 46% increase inforce. The increase in force provided by the straight pull over pivoting was related to the gripused. The grips that were found to produce higher forces were also more greatly improvedby using the straight pull over the pivoting at the wrists technique (for the 20mm size bag andlateral grip there was a 37% increase, but this was only 20% when using a finger pinch).

The different size bags were also different weights to simulate different sizes of packages soit is not possible to directly compare the data collected for each bag size. However, in theinterests of description differences will be discussed briefly although only for the straight pull

as pivoting at the wrists may have been effected by the bulk of the bags as well as the weight.The 60mm bag produced a 9.65N increase (a 33% increase) in force over the 40mm bagusing the power grip. The 40mm bag produced a 5.53N increase (a 39% increase) in forceover the 20mm bag using the lateral grip. The preliminary study into bag weight did notshow differences anywhere near this great so it would be logical to conclude that the largergrip area produces an increase in force.

The findings indicate that with non-disabled people, no more than approximately one-quarterof the variability in tear strength force exertion can be accounted for by differences in handanthropometry. For disabled people, although in some instances the proportions was higher,in general the indication were similar to those of non-disabled people.

A major difference between the disabled participants and the non-disabled participants wasthat the former often rested the unit on the work surface when attempting the trials. Incontrast the vast majority of the non-disabled group picked up the unit and held it about chestheight. The disabled participants rested the unit on their laps if they were wheelchair users.If they were stood up they may have had problems with their balance that meant they feltmore stable with the unit rested on the worktop. In addition the more frail participants mayhave had problems picking up the heavier unit with 500g or 1kg of weight added. The factthat they rested the unit on the worktop may have had an adverse effect on the amount offorce they could exert.

From qualitative data recorded during the study it is possible to identify a number of causesfor the impaired performance of the disabled participants. The tasks were impossible orpainful for some of the participants. The strengths at these tasks were dependent on the useof both hands so an individual was only as strong as their weaker hand. If a participant onlyhad the use of one hand then they could not take part. In some cases participants could onlycomplete certain tasks. They often found pivoting at the wrists more difficult probablybecause it involved awkward actions that were impaired by the dexterity related disabilitiessuch as arthritis that limits hand function. Many of the participants commented that theywould normally use their teeth or a pair of scissors to open such packaging.

3.3.7 Implications for packaging design

Previous DTI commissioned research has demonstrated the considerable problems disabledpeople and older people have when attempting to open different types of packaging. One ofthe most common reasons for failure to open packaging was the amount of force needed. Inorder to improve this situation and reduce the reliance on the use of tools such as scissors orknives (which it is known result in injuries), the strength capabilities of disabled people andpeople aged 51 years and over need to be taken into account.

The conclusions of this study demonstrate that the larger the area available for grasping andthereby allowing the use of a power grip, the more force can be applied to open a package.This should be clearly born in mind if people with limited strength capabilities – such asolder people and disabled people, are to be accommodated.

In determining acceptable forces for opening tear type packages, designers need to considerthe proportions of disabled people and people over 50 years of age that are accommodated asshown in this report. Clearly the minimum pull force required to tear open a package shouldbe as low as possible consistent with maintaining product integrity.

References

Anwall A. 1977. Handleability of consumer packages (unpublished). Swedish PackagingResearch Institute, Stockholm, Sweden.

Bobjer O, Johansson S-E, Piguet S. 1993. Friction between hand and handle. Effects of oiland lard on non-textured surfaces; perception of discomfort. Applied Ergonomics 24, 1993.

DTI. 1997. Domestic accidents involving plastic packaging. Consumer Affairs Directorate,Department of Trade and Industry. London.

DTI. 1999a. Domestic accidents related to packaging – volume 1. Consumer AffairsDirectorate, Department of Trade and Industry. London.

DTI. 1999b. Assessment of broad age-related issues for package opening Consumer AffairsDirectorate, Department of Trade and Industry. London.

DTI. 2000. A study of the difficulties disabled people have when using everyday consumerproducts. Consumer Affairs Directorate, Department of Trade and Industry. London.

DTI. 2002. Specific anthropometric and strength data for people with dexterity disability.Consumer Affairs Directorate, Department of Trade and Industry. London.

Ivergard G, Hallert I, Mills R. 1978. Handleability of consumer packaging – observationtechniques and measurement of forces. ). Swedish Packaging Research Institute, Stockholm,Sweden.

Martin J, Meltzer H, Elliot D. 1988. The prevalence of disability among adults. OPCSsurveys of disability in Great Britain. Report 1. HMSO. UK

Documents

Research into the forces required to open paper and sheet ...ergo-eg.com/uploads/books/forces required to open paper.pdf · and sheet plastic packaging – experiments, results and