BULE HORA UNIVERSTIY

COLLEG OF ENGINEERING AND TECHNOLOGEY

DEPARTMENT OF INDUSTRIAL ENGINEERING
COURSE NAME: ERGONOMICS AND INDUSTRIAL SAFTY

TITLE: DESIGN AN ADJUSTABLE SITTING CHAIR

COURSE CODE:

Prepared by:-

Name ID No
1. Anteneh
2. Beyene Hasen RU\1497\11
3. Bezenaw Aschalewu RU\1365\11
4. Eliyas Tadesse RU\1504\11
5. Gadisa Alula RU\1508\11
6. Lemiya Bedewi RU\1378\11
7. Raji Shiwa RU\1386\11
8. Seadi Jibril RU\1570\11
9. Toshi Musa RU\1351\11
10.Yadsa Gonfa RU\1798\11
Submitted to: Mr fitsum
Submission Date: 25/04/2014 E.C

JENUARY, 2022
BULE HORA, ETHIOPIA
 Design an Adjustable Sitting Chair

Table of content
Content PAGE
No
Table of content................................................................................................................................I
List of Figure...................................................................................................................................II
List of Table...................................................................................................................................III
Abstract..........................................................................................................................................IV
CHAPTER ONE..............................................................................................................................1
1. Introduction..................................................................................................................................1
1.1 Background.........................................................................................................................1
1.2 objective of the project.......................................................................................................2
1.2.1 General objective...........................................................................................................2
1.2.2 Specific objective .......................................................................................................2
1.3 statement of the problem....................................................................................................3
1.3.1 Musculo SkeletaL Disorders (MSD).............................................................................3
1.3.2 Ergonomics Risk Factors...............................................................................................3
1.3.3 Repetitive Motions.........................................................................................................3
1.3.4 Posture............................................................................................................................4
1.3.5 Vibration........................................................................................................................4
CHAPTER TWO.............................................................................................................................5
2.LITERATURE REVIEW.............................................................................................................5
2.1 The Basic Elements of Ergonomic Program In Any Workplace........................................5
2.2 The Importance Of Ergonomic..........................................................................................8
CHAPTER THREE.........................................................................................................................9
3.RESERCH METHODOLOGY....................................................................................................9
3.1. Participants and Sample Size in Project............................................................................9
3.2. Anthropometric Measurements.........................................................................................9
3.3 Data collection..................................................................................................................12
3.4. Data Analysis...................................................................................................................13
CHAPTER FOUR..........................................................................................................................14
4.RESULT AND DISCUSSION...................................................................................................14

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4.1 Result................................................................................................................................14
4.2 Discussion.........................................................................................................................15
CHAPTER FIVE...........................................................................................................................19
5.CONCLUTION...........................................................................................................................19
REFERENCES..............................................................................................................................20

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List of Figure
Figure 3.1 Anthropometric dimensions required in chair design.................... 11
Figure 4.1 shows the designed chair from different sides................................ 15

Department Industrial Engineering ,BHU

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 Design an Adjustable Sitting Chair

SYMBOLS AND ABBREVIATIONS

ST............................. stature
SB............................. shoulder breadth
CD............................ chest depth
SH.............................. sitting height
SHE............................ sitting eye height
SSH........................... sitting shoulder height
PH............................. popliteal height
SKH......................... sitting knee height
FHL.....................forearm hand length
SHE.................... sitting elbow height
TC.....................thigh clearance
HL....................head length
HNL................ hand length
HND................. hand depth
HB....................hip breadth
FL...................... foot length
FB.......................foot breadth
EEB................ elbow to elbow breadth
EH.................. elbow height
MH................ malleolus height

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Abstract
Proper designing of chairs based on ergonomics increases efficiency, promotes quality of
education, leads to correct posture in students, and reduces risk of musculoskeletal disorders.
The aim of this project was to design and develop an ergonomic chair, based on anthropometric
data of students in educational settings. Anthropometric parameters were obtained from a
stratified-random sample of 20 students. The data were analyzed and the results were extracted
as mean, standard deviation, and percentiles. The chair was planned in the CATIA software and
developed by a three-dimensional print. In this project, an ergonomic chair was designed based
on anthropometric data from students. The seat height, depth, and width of the chair were
determined as 44 cm, 42 cm, and 42.15 cm, respectively. The height of the desk was adjustable in
19 to 29 cm, and the depth and length of the desk were considered as 51 cm and 65 cm. The
width and height of the backrest were also 54 cm and 44 cm, and the backrest angle was
adjustable in 95° to 105°. An ergonomic chair with adjustable parts was designed to achieve a
well-match between anthropometric characteristics of students and the furniture. Such chair can
reduce musculoskeletal disorders in students. Some ergonomic characteristics of this chair
include adjustability of footrest, backrest, armrests, and desk. A chair with such characteristic
can be used by many students with different body sizes

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CHAPTER ONE
1. Introduction
1.1 Background
“The scientific discipline concerned with understanding of interactions among humans and other
elements of a system, and the profession that applies theory, principles, methods and data to
design in order to optimize human well-being and overall system performance”. Ergonomics
means “fitting the job to the worker” From the Greek

Ergo = Work
Nomos = Laws1

Ergonomics can be defined as the study of work. It is the science of designing the job to fit the
worker, rather than physically forcing the worker’s body to fit the job. Ergonomic is not a new
science, for the first time it was used in 1857 by a polish Scholar. However it is still a new
science for the most under developed countries including Ethiopia Generally, term ‘fit’ between
people and their work has been concerned by Ergonomic program since long time ago.
Limitations and capabilities of people have been taking account as a priority. The main aims of
Ergonomics are making sure of fitting workers with the environment, information, tasks and
equipment. (2, 3, 4, 5) Based on many researchers, the common definition of Ergonomics is “the
study of work” More specifically, “it is the science of designing the job to fit the worker, rather
than physically forcing the worker’s body to fit the job”. ( 6,7,8,9,10)
It can be applied in many
scientific disciplines such as industrial hygiene, psychology, kinesiology, physiology and
anthropometry.(11,12)Education is the most effective means to ensure economic growth and
national development in countries (13).University is one of the educational settings in training of
students. Effective training can be achieved in a safe and stress-free space in classrooms (14).
Physical environment of educational facilities can help teaching, learning, and academic
performance (15, 16), while inadequate facilities can cause stress and agitated behaviors in
students (17). Physical environments of classrooms have a vital role in student’s satisfaction
(18), and a higher level of satisfaction can increase the level of skills, mentality, and knowledge
of students (19). University is the workplace of many students around the world, and chairs have
become an important physical element of the classroom and learning environment (20, 21).
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Educational furniture is used in classrooms of many colleges, institutes, and universities (22, 23)
and students spend a major part of their time sitting on this furniture in classrooms or lab (24,
25). Therefore, they are exposed to risks associated with prolonged sitting in a static and
awkward posture. These risk factors are generally created with inappropriate chairs.Improper
design of chairs is one of the reasons of inappropriate sitting positions which can lead to bad
posture, fatigue, severe psychological stress, and effects on students’ performance. The
relationship between awkward body posture and cognitive issues, such as consciousness,
discomfort, and reaction time has also been investigated by some studies. Many complications
can arise from using inappropriate chairs, such as lower back pain, pain in the spine, neck,
shoulders, arms, and paralysis of muscles.Anthropometry has three basic principles that are
being considered in designing various furniture, depending on their type. These principles
include: “Design for extreme”, which can be designed based on the 95th percentile male or
design based on the 5th percentile female; “design for an adjustable range”, which can be
considered both 5th female and 95th male and this principle has been suggested by many
researchers in designing; “design for the average”, which is used whenever the use of
adjustability is impractical (20). This study used principles of “design for extreme” and “design
for an adjustable range” for designing different parts of a chair.

1.2 objective of the project

1.2.1 General objective
The main objective of this project was to design and develop an ergonomic chair, based on
anthropometric data of bule hora university computer science laboratory.

1.2.2 Specific objective

 Over viewing of Ergonomic program and studying Ergonomic risk factors.
 To define ergonomic clearly. From the project, it was found that ergonomic save money and
improves quality, productivity, employee morale and create better Safety culture.
 Employees shall recognize the ergonomic risk factors and solutions to minimize such risks.
 Management and training program

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1.3 statement of the problem

On the computer science laboratory the chair is not design ergonomically so it affects students in
different way like disorder on natural ‘s’ shape of the spine, highly risk of slumping and stress on
the spine and the pelvis. And they may affect by the following disorders

1.3.1 Musculo SkeletaL Disorders (MSD)

Any injury or disorder related to musculoskeletal system is called “musculoskeletal disorders”
which the consequences of workplaces’ risk factors. The MS consists of bones, muscles,
ligaments, tendons, joints … etc. Alternative terms which have been used in other studies instead
of MSDs are “Repetitive Strain Injury, Musculoskeletal Injury, Cumulative Trauma Disorder,
Occupational Overuse Syndrome, or Strain or Sprain”. All parts of body likely to be impacted by
MSDs including lower and upper limbs, for example feet, legs, wrists, shoulders, neck and so on
(30).

1.3.2 Ergonomics Risk Factors

Any bio mechanical stress on the workers, resulted from their jobs or tasks is called ERF. The
balance between Individual’s ability and soft tissue fatigue is the key factor to be recovered from
MSD’s formation. To prevent such injuries, recognizing ergonomics principles is very important.
Thus, students shall be familiar with ERF in regards to their works and methods of reducing such
hazards (31).

1.3.3 Repetitive Motions

For such tasks that have motion cycle less than a minute for a period more than two hours
without taking rests, fatigue can occur and this will lead to accumulate muscle strain (32). Pain,
visible swelling, numbness, redness, loss of strength and flexibility of affected area, tingling are
resulted in “repetitive motion disorder” (33).

1.3.4 Posture
A. Awkward Postures

One of the primaries ERF is awkward posture, when the working surface height is not correct,
the worker is likely to expose awkward posture. Body’s part could be affected seriously with

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working at too high which may need to put body part such as shoulders, neck, arms and so on in
uncomfortable condition. Unlikely, working with too low surfaces will the lower back and neck
in a terrible ways (34).

B. Static Postures

Unlike Awkward postures, Static postures means to keep a part of body for a period of time
unmovable or when a part of body required to be stopped in movement for a period of time for
such task. For instance, when someone works on computer for few hours without taking rests, it
absolutely impacts his or her neck and leads to disorder (35).

1.3.5 Vibration
When a part of body subjected to a vibrating object, it leads to injury and other health’s
discomforts. To give a clear example, fingers and wrists could be injured or subjected to some
other health problem due to the using power hand tool without considering ergonomic principles.
Another example, Loaders or excavators could be a source of whole body vibration to the
operator, if he or she does not practice ergonomic program (36 & 37 )So we decide to design an
adjustable sitting chair based on their anthropomorphic data

1.4 SIGNIFICANCE OF THE STUDY.

The significance of this study was gives comfortable and adjustable siting chair to the students
and provides the correct posture for great structure and minimal injury. Ergonomics refers to the
design of your workplace – your furniture, equipment, and operational space, and how your body
functions amongst these all. Optimizing the best support, postures, and positions for your body
while conducting your job greatly affects how well you perform your tasks and how you function
in your workspace. It is important to choose sitting chairs with back support. Back support when
sitting for extended periods of time is essential to maintain spinal, joint, and muscle integrity.
These key elements of bodily function need to be correctly supported and maintained to prevent
injury, joint damage, and muscle strain.

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CHAPTER TWO
2.LITERATURE REVIEW
The term ergonomics comes from the two Greek words “ERGON” which means labor or work
and “NOMOS” which means natural laws. In 1857, the word ERGONOMIC has been used for
the first time by a Polish scholar which is called “Wojciech Jastrzębowski” and published a book
with title “Ergonomics or Science of works”. Through the history, in the age of Roman, Egypt
and Greek, the work related health problem always has been reported. Moreover, an Italian
physician who is called “Bernardino Ramazzini” (1633-1714), he stressed that the most
systematized from occupational health perspective is the right link between pathology and
working condition.(26)Another scientist from Poland which is called “Józefa Joteyko”, published
a book in English and titled with “The Science of Labor and Its Organization”, in 1919. In his
book occupational fatigue and principles have been explained in detail. In 1921, a good paper
“Research of Efficiency: Ergonomics” was published by a Japanese scientist, Kan-ichi Tanaka
(27). In the 1950s, many good textbooks have been published by American scholars such as
Sanders, McCormick and Woodson. Another good book “Fitting the Task to the Man” published
by Grand jean, in 1963 (28).The “International Ergonomics Association” (IEA) was founded in
1959 (29), is one of the most famous organization which works on ergonomic program and it has
published many manual, guidelines and papers related avoiding work related risks. In addition,
many international conferences have been held by this organization every three years in different
countries around the world including Birmingham, Stockholm, Sydney, Tokyo, Beijing and
many mores.

2.1 The Basic Elements of Ergonomic Program In Any Workplace

The main aim of safety program is eliminating or decreasing incidents, accidents and injuries by
removing or reducing of their root causes. Based on many organizations with good safety
performance, ergonomic program is the best choice to achieve this goal. Having successful
ergonomic program depend on several elements. Especially, training and education are
considered as critical element of a successful ergonomic program, as it can familiarize workers
with such principals such as risk identification, risk reduction, injuries management etc., which

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are essential for ergonomic improvement process. It can increase the worker’s potential
regarding skills, abilities and knowledge to execute their intended obligations. Besides training

and education, management, employees’ participation, development of solutions and program

evaluation are also essential elements of successful ergonomic program. It can be seen in the

Key elements Successful ergonomic program

Management Focusing the employer’s belief on necessity of ergonomics

program Appointing persons in charge for ergonomic program
execution Establishing goals
Training Increasing knowledge of ergonomic
Improving skills & abilities in reducing ergonomic hazards
Employees participation Enhancing Job satisfaction
Enhancing motivation
Creating team Improving communication
Program evaluation Auditing of targeted performance
Evaluating of program efficiency
Ergonomic hazards identification
Development of solution Controlling development to mitigate hazards
Appropriate engineering
Appropriate work practice controls PPE ( Personal Protective
Equipment)
Administrative control
Key elements Successful ergonomic program
Management Focusing the employer’s belief on necessity of ergonomics
program Appointing persons in charge for ergonomic program
execution Establishing goals
Training Increasing knowledge of ergonomic
Improving skills & abilities in reducing ergonomic hazards
Employees participation Enhancing Job satisfaction
Enhancing motivation
Creating team Improving communication
Program evaluation Auditing of targeted performance
Evaluating of program efficiency
Ergonomic hazards identification
Development of solution Controlling development to mitigate hazards
Appropriate engineering
Appropriate work practice controls PPE ( Personal Protective
Equipment)
Administrative
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2.2 The Importance Of Ergonomic

a. Saves money: Based on many studies, 1$ out of 3$ of worker compensation costs are due to
MSDs related problem.

b. Improves productivity: Increase the workability of labors by fitting the jobs to the workers .

c. Improves quality: stress on training courses, emphases on using high quality tools and
equipment. This leads to improve the skill of workers.

d. Improves employee engagement: employees get interested when the company attempt to
compliance with standard of health and safety. This increase morale and labor involvement. As a
result, it reduces absenteeism and turnover.

e. Creates a better safety culture: the cumulative of above point shows the commitment of
company or employers and this change employees view towards safety to safety culture.

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CHAPTER THREE
3. RESERCH METHODOLOGY
3.1. Participants and Sample Size in Project,

Anthropometric parameters were obtained from students of bule hora University of computer
Sciences. The total number of students was 34. Sample size was calculated. However, collected
data exceeded the calculated sample size, and 10 students participated in the project. In this
project, male and female students at the age of 20 to 24 years, studying at undergraduate levels,
were selected through stratified-random sampling

3.2. Anthropometric Measurements

Static anthropometry was used to measure dimensions of the body. Data of static anthropometry
are related to dimensions and sizes of the body in a fixed structural position that are measured by
specific anatomical points in a specific condition. An anthropometric with adjustable chair and
footrest, digital calipers with precision of 0.1 and 0.5 mm, plastic ruler, flexible measuring tape,
and a goniometer were used to measure the body dimensions of students. Then, the results were
recorded in an anthropometric checklist. Subjects wore a light dress with no shoes. All
measurements were taken when the subjects were sitting in a full straight posture, so that the
knees and ankles formed right angles and with feet on the floor. The recorded anthropometric
measurements were stature, sitting height, shoulder height (sitting), elbow height (sitting),
shoulder breadth, popliteal height, knee height, hip width, elbow to elbow width, elbow-fingertip
length, buttock-popliteal length, buttock-knee length, abdominal depth, forearm width, thigh
thickness, and weight. Definitions of the above mentioned anthropometric dimensions are
presented

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3.3 4table3.1 description of dimensions of the body for design of the classroom chair
Body Dimensions Description of Body Dimensions of Student
Stature Vertical distance from the floor to the top of the head, and
measured with the subject erect and looking straight
Sitting height. Vertical distance between the top of head and the surface of
the seat surface that measured with the subject erect and
looking straight ahead
Shoulder height sitting Vertical distance from the top of the shoulder at the
acromion to seat surface
Elbow height sitting Vertical distance from the bottom of the tip of the elbow to
the seat surface and taken with a 90° angle elbow flexion.
Shoulder breadth Maximum horizontal breadth across the shoulders
Popliteal height Vertical distance from the floor to the posterior surface of
the knee with 90° knee flexion.
Knee height. Vertical distance from the floor to the top of the knee cap
Hip width Horizontal distance measured in the widest points of the
hips in the sitting position
Elbow to elbow length Horizontal distance across the lateral surfaces of the elbows.

Elbow-fingertip length Horizontal distance from the outer surface of the elbow to
the tip of the tallest finger
Buttock-popliteal length Horizontal distance from the posterior surface of the
buttock to the popliteal surface
Buttock-knee length Horizontal distance from the back of the buttock to the front
of the knee cap
Abdominal depth Horizontal distance from vertical reference plate to front of
the abdomen in standard sitting position
Forearm width Maximum width of the forearm when it is straight.

Vertical distance from the highest point of thigh to the seat

Thigh thickness surface.

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Figure3.1 Anthropometric dimensions required in chair design.

Abbreviations: S, stature; SH, sitting height; SHH, shoulder height; EHS, elbow height sitting;
SHB, shoulder breadth; PH, popliteal height; KH, knee height; HW, hip width; EW, elbow to
elbow width; EFL, elbow-fingertip length; BPL, buttock-popliteal length; BKL, buttock-knee
length; ABD, abdominal depth; FW, forearm width; TT, thigh thickness.

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3.3 Data collection

Table 3.2 4 Anthropometric data of female and male students
Anthropometric Parameters Male female

5th 95th Mean ± SD 5th 95th Mean ± SD

Stature 164 186 176.5 ± 154 170 162.6 ±
6.66 5.32
Sitting height 86 98.8 92.2 ± 38.2 81 91 85.5 ± 3.08
Shoulder height (sitting) 57.15 68.5 63.3 ± 3.15 54.65 62.85 58.4 ± 2.52
Elbow height (sitting) 18.65 29 24.9 ± 3.15 19.3 29 24.2 ± 2.57
Popliteal height 36 44.5 40.9 ± 3.43 33 41 37.5 ± 2.54
Knee height 47 62.85 51.7 ± 2.85 44 53 48.4 ± 2.42
Shoulder breadth 34.09 42.39 37.8 ± 2.27 32.18 38.55 35.6 ± 2.01
Hip width 32.37 40.6 36.5 ± 2.27 32.92 42.15 36.9 ± 2.69
Elbow-fingertip length 44.13 51.18 47.4 ± 2.07 38.8 45.6 42.4 ± 2.17
Buttock-popliteal length 46.15 58 50.4 ± 3.28 42 52 46.8 ± 2.95
Buttock-knee length 57.15 69.7 62.2 ± 3.42 54 64 58.6 ± 3.19
Abdominal depth 21 28 24.3 ± 2.15 19.3 28 22.9 ± 2.81
Forearm width 6.8 9.49 8.1 ± 0.8 6.09 8.5 7.19 ± 0.73
Thigh thickness 13 20.42 16.1 ± 2.34 11 18 13.9 ± 2
Elbow to elbow width 35.76 51.93 43.7 ± 5.37 34.64 46.85 40.22 ±
3.83
Weight 55 87.82 70.3 ± 9.6 44 74.1 57.8 ± 9.73

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3.3 4Table 3.3 Anthropometric data of all students

Anthropometric Parameters
All Students
5th 50th 95th min max Mean ± SD
Stature 155.2 166.5 184 149 203 168.1 ±
9.01
Sitting height 81 88 96.8 78 103 88.1 ± 4.73
Shoulder height (sitting) 55 60 67 52.5 70 60.4 ± 3.75
Elbow height (sitting) 19.2 24.5 29 17 36 24.5 ± 2.83
Popliteal height 33.7 39 43.5 29 63 38.9 ± 3.36
Knee height 45 50 55 43 59 49.7 ± 3.08
Shoulder breadth 32.41 36.44 40.74 31.3 44.42 36.46 ±
2.36
Hip width 32.68 36.73 41.33 31.2 45.24 36.76 ±
2.54
Elbow-fingertip length 39.3 44.15 49.76 34.2 52.36 44.37 ±
2.23
Buttock-popliteal length 43 48 55 38 61 48.31 ±
3.57
Buttock-knee length 54.5 60 66.3 49.1 72 60.1 ± 3.71
Abdominal depth 20 23 28 16 34 23.47 ±
2.66
Forearm width 6.28 7.47 9.27 4.46 9.96 7.6±0.88
Thigh thickness 11.5 14.93 19.18 9 23 14.78 ± 2.4
Elbow to elbow width 35.17 40.92 51.08 23.53 56.15 41.58 ± 4.8
Weight 44.4 62 80.9 41 99 62.8 ±
11.45

3.4. Data Analysis

The results were extracted as mean, standard deviation, and percentiles. Thereafter, standard
dimensions for designing an ergonomic chair were estimated. Then, the prototype of the chair
was developed by three-dimensional print. The material assumed for developing this model was
PLA bio plastic

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CHAPTER FOUR
4.RESULT AND DISCUSSION
4.1 Result
According to the percentage= (amount*100)/base, 6 (17.65%) of cases were female, and 28
(82.35%) were male; Mean and standard deviation of age was 21.82 ± 1.55 years. Descriptive
statistics of anthropometric parameters for males and females and all students are presented in
Tables 3 and 4 Table4 shows various criteria, which have been suggested to determine the
dimensions for designing chairs for students. Two principles of anthropometry were used to
determine these criteria, which include “design for extreme” and “design for an adjustable
range”. For example, principle of “design for an adjustable range” was used for designing the
height of the desk. It should be noted that in this Project, different dimensions of the designed
chair were compared with standard

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4.1 5Table 4.1The result of mesurement of the designed chair

Chair Features Design Anthropometric Data Dimension Criteria Determinant

(Cm)
Seat height Popliteal height 44 5th percentile (female) of popliteal
height
Seat depth Buttock-popliteal 42 5th percentile (female) of buttock-
length popliteal length
Seat width Hip width 42.15 95th percentile (female) of hip
width
Desk height Elbow height (sitting) 19 – 29 5th – 95th percentile (all) of elbow
height
Desk length Elbow-fingertip 51 95th percentile (male) of elbow-
length fingertip length
Desk Elbow to elbow width 65 width 95th percentile (male) of
elbow to elbow width
Armrest width forearm width 9.49 95th percentile (male) of forearm
width
Backrest height Shoulder height 54 5th percentile (female) of shoulder
(sitting) height
Backrest width Shoulder breadth 44 width 95th percentile (male) of
shoulder breadth
Backrest angle - 95° - 105° Bs5873

The data collected in this project can be used for designing adjustable and non-adjustable chairs
for students. In many researches it has been recommended to design adjustable furniture
whenever possible. However, factors, such as cost, difficulty to prepare, mechanism of
adjustability and time make limitations in designing and development of adjustable furniture. In
this project, some parts of the chair were designed to be adjustable in order to allow comfort and
flexibility.

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Figure 4.1 shows the designed chair from different sides.

4.2 Discussion
Long-term inappropriate posture and discomfort, associated with improper design of chairs and
desks used at schools and universities, are factors that may affect learning and academic
performance and physical growth of students. Therefore, chairs should be designed based on
anthropometric dimensions of users. Matching between dimensions of chairs and users’
anthropometric dimensions and ergonomics indices leads to more comfort for consumers.
Standard design of chairs can promote anatomical postures and comfort, which prevent
inappropriate body postures. This factor can also reduce the risk of musculoskeletal disorders
and increases efficiency and concentration of students at classrooms (13, 23, 26). In this project,
an ergonomic chair was designed based on ergonomics principles and anthropometric data
obtained from students to allow comfort and productivity. Anthropometric dimensions that form
the basis for the dimension of seat height was the popliteal height and the seat height of standard
chair in this project was determined based on the 5th percentile of females’ popliteal height. The
seat height of the chair should be matched with 5th percentile of users’ popliteal height so that
short persons are also able to put their feet on the floor easily and do not feel pressure in different
parts of their body when sitting on the chair. In this project, standard seat height without
considering shoes was 33 cm, which is consistent with findings of similar studies (2, 41).
Furthermore, with 3 cm for heel height and 8 cm for the height of footrest, the seat height was
considered 44 cm, which is in accordance with BS5873 and standard ISIRI 7494. this dimension
was considered 44.5 cm, which is similar to the our project. The footrest of the designed chair

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was adjustable for short persons, who cannot fully fit their legs on the floor, if they want to place
their legs on this footrest. Also, tall persons can fully close it if they do not want to use the
footrest. A basket is also available under the chair for additional equipment The seat depth was
calculated 42 cm based on 5th percentile of buttock-popliteal length, which matches the standard
BS5873 and ISIRI 7494. This figure was reported as 40.9 cm (2) and 40 cm (40) in other studies,
which are less than that obtained in the our project. In contrast, some studies reported this
dimension as 43.4 cm (8), 44.81 cm (16), and 45 cm (9), respectively, which is more than the our
project. Mismatch between seat depth and buttock-popliteal length of users can lead to bending
of the trunk and head and extending the arm forward and, consequently, leading to pain in the
back, shoulders, and arms in the long term and also creating problems in using the backrest. The
high depth of seat leads to pressure on the thighs and disruption of the circulatory system; the
low depth of the seat leads to pressure on back and knees to avoid falling (42). The front edge of
the seat has a curvature that protects the underlying thighs, and the casualty in front of the seat
prevents from pressure to different parts of the feet. This feature is in accordance with the ISIRI
9697 - 1 standard. The hip width was considered for determining the dimension of the seat width.
The standard seat width was determined based on the 95th percentile of hip width that was
reported as 42.15 cm. This figure in the study of Zarei et al. (2) and Kashif et al. (16) was
reported as 41 cm and 30.03 cm, respectively, which is less than those calculated in our project.
This dimension was estimated as 43 cm (9) and 43.6 cm in other similar studies (8). The seat
width in the designed chair in this study was considered as 45.5 cm due to increase in the thighs
clearance, which is in accordance with BS5873 and standard ISIRI 7494. This chair also has an
armrest on both sides; therefore, the seat width was considered larger so that it did not create any
problem and limitation in sitting and standing up. Therefore, this factor causes people to feel no
pressure on their hip and the sides of thighs when sitting on it. The desk of the designed chair
was adjustable, and adjustable height of this desk was determined by 5th to 95th percentile of
sitting elbow height of all students, which was 19 to 29 cm. The height of the armrests and the
desk of the chair were adjustable because different people can adjust the height of their elbows
and place it along their elbows so that they do not keep their shoulders up or down and feel no
pressure on the shoulders and various parts of their hands. According to Grimes, mismatch
between the sitting elbow height and desk height can lead to pain in the shoulders and neck (43).

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The adjustability of the desk in the study of Kashif et al. was reported as 22.64 to 24.26 cm (16),
and in the study of Taifa and Desai, it was reported as 15.6 to 24.5 cm (9), which are in
contradiction with the present project. One of the reasons for the conflict was that these studies
were conducted in different countries; consequently, the body dimensions of students were
different from country to country. In some studies, such as Thariq et al.’s research, this
dimension was not considered adjustable, and a fixed height of desk was estimated as 22.9 cm
(8). It should be noted that the softness of hand placement on the elbow support in the designed
chair is based on the recommendation of Pheasant. The 95th percentile of elbow-fingertip length
of male students was used to determine length of the desk and this dimension was 51 cm. This
size in Zarei et al.’s study was 50 cm, which had one centimeter difference with the current study
(2). In similar researches, this dimension was different from the current study (8, 9). One of the
reasons for this contradiction was the difference in dimension and percentile used in the
mentioned studies, so that they used from buttock-knee length (9) and 50th percentile of
elbowfingertip length (8) for this purpose. The desk of the chair designed in the present study
had the ability to move forward and backward, which makes it easy for people to adjust the desk
at the desired distance from their body. This also causes people with high abdominal depth to sit
comfortably without pressure. This desk can be folded and stepped out of the chair and the
students can close the desk if they do not want to use it. Desk width was obtained as 53.93 cm
based on 95th percentile of elbow to elbow width and due to the design requirements and
ensuring that the desk was placed on the chair’s armrests; this dimension was considered 65 cm.
The surface of the desk was considered wide enough to be suitable for both right-handed and
left-handed students and the person should not bend the waist and neck when writing. Also, there
was enough space to put additional stationery, and it had a groove where students could put their
pen and pencil. Armrest width was determined based on 95th percentile of forearm width to the
elbows and forearms of the majority of students were appropriately positioned on it. On this
chair two armrests were considered to support both arms. Shoulder height was used in
determining the height of backrest and the percentile used for this purpose was 5th percentile and
this design facilitated the movement of the waist and arms (32). Also, the upper part of the
backrest had two grooves to place the students’ bag. The backrest height in the study of Taifa
and Desai was reported as 50 cm, which was different from the current study (9) because of

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differences in studied countries and people. The upper and lower edges of the backrest were
considered in a curved form, based on the ISIRI 9697 - 1 standard. The backrest width of the
chair was calculated as 44 cm based on 95th percentile of student’s shoulder breadth and
standard ISIRI 7494, and the curvature of this backrest supported the lumbar well. In some
studies, this dimension was reported as 43.6 cm (8) and 42 cm (9), which was similar to the
current study. Mismatch between the backrest width and shoulder breadth can lead to fatigue of
the scapula and pain in the shoulders (2). The backrest angle should be adjustable to provide full
lumbar support and posture of students can be proper and varied (16). Therefore, one of the
features of this chair was its ability of adjustment to the backrest angle, which has a pin for the
person to adjust the backrest at the desired angle for comfort. The adjustable angle of backrest
was considered from 95° to 105°, based on British Standard (BS5873) and standard ANSI-HFES
100/1988. Backrest angle in other similar studies was 96° (8), 100° (40), and 110° (9) and was
not adjustable. This adjustability in the study of Kashif et al. was from 100° to 120° (16). These
differences were due to used standards in these studies. The desk angle in this research was
considered 0°, which is in line with Thariqetal.’s study (8) and is different from the study of
Taifa and Desai that reported this angle as 0° to 20° (9). Also, in the study of Khanam et al., this
angle was considered as 10 degrees, which is different from our project (40).

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CHAPTER FIVE
5.CONCLUTION
An ergonomic chair with adjustable parts was designed to achieve a good match between
anthropometric characteristics of students and used furniture. The size of the chair was based on
anthropometric dimensions of students. Since most activities of students are done while sitting
on the chair, the ergonomic design of the chair is important for students. Thus, taking action to
correct the existing chairs is important in terms of physical health of students and economic
sentiment as physical problems associated with improper sitting conditions would lead to
financial and medicinal costs. The chair designed and developed in this Project was ergonomic
and helped to reduce musculoskeletal disorders in students. Some ergonomic characteristics of
this chair included adjustability of footrest, backrest, armrests, and desk and these factors led to
the use of this chair by many students with different body sizes. The edges of the seat had a
curvature that prevented pressure to different parts of the body and created comfort for users.
Other advantages of this chair that distinguished it from other educational chairs includes
adjustable footrest so that legs can be fully fitted, adjustable height of desk and left armrest, desk
rotation in two axes of X and Y, adjustability of angle between the backrest and seat in four
degrees, large surface of the desk, grooves on the backrest to place bags, a groove on the desk to
place pens and pencils. One of the limitations of this study was the inability of seat height
adjustment and lack of angle adjustability in the desk, which are technical limitations in
constructing the chair

6. RECOMMENDATION
There are some anthropometric mismatches in seated work like the desk is too high (above
elbow height) and seat too high (elbow rest too high).so we recommend this university to provide
the ergonomically designed sitting chair in computer laboratory by identifying the
anthropometric data for the students. Because the back rest of the computer laboratory chair is
too short for the students, provide higher back rest to avoid back aches and to make their seat
more comfortable and relax. The other existing dimension of the chair can retain or no need to
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change. For the computer laboratory table, lower the height so that the students may avoid hand
muscles pain and the computer keyboard may be use so comfortably and relax. Also we
recommend this university computer laboratory class room to use a height adjustable chair or
desks for the compatibility of the students with their respective body measurements to the height
of chair and table. These also help to prevent the mismatches in seated work. For the future, this
study can use as basis for their study regarding the workstation of offices and for the chairs in
classrooms concerning the anthropometric measurements.

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