30120140504006

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 38-50 © IAEME
38
SAFETY FEATURES MODELING FOR INTEGRATION IN DESIGN
PROCESS
Wolfgang Nzié1
, Jean Bosco Samon2
, Bonaventure Djeumako3
1
Senior Lecturer, Department of Mechanical Engineering, National School of Agro-Industrial
Sciences, The University of Ngaoundere, Cameroon
2
PhD Student, National School of Agro-Industrial Sciences, The University of Ngaoundere,
Cameroon
3
Senior Lecturer, Head Department of Mechanical Engineering, National School of Agro-Industrial
Sciences, The University of Ngaoundere, Cameroon
ABSTRACT
Although a process or plant can be modified to increase inherent safety at any time in its life
cycle, the potential for major improvements is greatest at the earliest stages of process development.
At these early stages, the process engineer has maximum degrees of freedom in the plant and process
specification. The engineer is free to consider basic process alternatives such as fundamental
technology and chemistry and the location of the plant. The modeling of inherently safer process
alternatives that we call safety features to be integrated in the process design is the main objective of
this paper. This is because each CAPP domain (assembly, machining, inspection, safety, etc) has
been treated independently. And the “feature-recognition” has been adopted as the unifying theme.
Indeed integrate safety during the life period of machines is costly and sometimes destructive. For
that purpose to be achieved safety features are defined and taxonomy attributed based on the function
of the features. They are then classified into two main groups which are safety features incorporated
in machine and those out of machine. These features are equally given nine criteria to characterise
them. The study also presents an algorithm showing the safety integration optimization in earliest
design stages.
Keywords: Modeling, Features, Integration, Safety, Design Process.
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
AND TECHNOLOGY (IJMET)
ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 5, Issue 4, April (2014), pp. 38-50
© IAEME: www.iaeme.com/ijmet.asp
Journal Impact Factor (2014): 7.5377 (Calculated by GISI)
www.jifactor.com
IJMET
© I A E M E

39
1. INTRODUCTION
Computer-Aided Process Planning (CAPP) has long been recognized to be an important
component and enabler of Concurrent Engineering (CE). Proposed structures of generic CAPP
support systems with CAD data (object Information) exist [1-3]
Design is the synthesis, the putting together, of ideas to achieve a desired purpose [4]. The
design process does not only consider the final purpose but equally looks at other important aspects
amongst which is safety. Safety is defined as freedom from those conditions that can cause death,
injury, occupational illness, damage to or loss of equipment or property, or damage to the
environment [5]
Hale et al. (2007) make it clear that design errors are the causes of 20 to 60 percent of the
accidents on installations. These errors are more rampant in new design since only proactive
information is available and there is still a gap between the designer’s view and the user’s view
which equally needs to be considered in the design process [6]. Users in order to correct the errors or
reduce the risk associated carry out modifications on the system which is costly and can be
destructive.
To solve this problem of cost and destruction, the modifications done can be integrated in the
upcoming design in the form of features. This is based on the fact that design is the first stage in
system’s development and so design offers the earliest, and hopefully the cheapest place to intervene
and get it right. This time around, the design process is both proactive, projecting new designs into
their future use situations, and reactive, feeding back experience gotten from using earlier designs. In
other words, it needs to incorporate both explicit and implicit modalities [7].
It is in this light that this project treats the safety modelling features for CE purpose. The
specific objectives set to help in attaining the objective above are:
• Modelling of safety features (definition, identification, taxonomy (classification) and
characterisation of safety features);
• Integration of safety in process design (representation of the design feedback process and
establishment of an algorithm which can be followed to integrate safety in design based on
risks presented by already existing machines);
To achieve these objectives, this work will begin with a literature review, which will be
closely followed by a description of the materials and methods used. Then the results obtained will
be presented and discussed and work will then be crowned with a conclusion.
2. LITERATURE REVIEW
2.1 The different aspects of safety
Generally, safety in an industry refers to four aspects. The first aspect of safety is related to
the installation which in most cases is made up of the machines in the production line. The
production line takes in raw materials and sends out finished products. Thus the next aspect
considered is the safety of the product. Equally the installations need man power (personnel)
consisting of those who intervene directly or indirectly on the installations to ensure a proper running
of the process. This is the most vital aspect since it deals with human life. Lastly, there is safety with
regards to the environment which is also very important since human beings make up part of the
environment.

40
2.2 Features and their classification
Different authors define features in different ways. Dixon et al. (1987) say a feature should be
comprehended as a professional terminology which has attribute of both form and function and the
name and meaning of which can be associated with its special geometrical form, topological relation,
typical function, drawing expression, manufacturing technology and tolerance demand [8]. Motavalli
et al. (1997) emphasize that a feature is defined by the specific syntax and contains data such as
mathematical representation; classification which can be either protrusion or depression; orientation
with respect to other features or user defined coordinates system; and its geometric and topological
structure [9]. The tolerance demand mentioned in the above definition is a geometry data which
describes the manufacturing requirements of a particular feature. Some manufacturing related data
such as tolerances can also be added to the feature geometry data to describe manufacturing
requirements of a particular feature. Other definitions of feature include that of Nzie (2002) where a
feature is a group of characteristics (information), relative to the geometry, technology, functions and
other attributes of an object such that it can be used in the domains that intervene in the design
process [10]. A feature can also be seen as a representation of shape aspects of a product that are
mappable to a generic shape and functionally significant for some product life-cycle phase [11].
Feature classification varies from one author to another depending on his needs. Pratt
classifies features according to their domain of application [12]. Wenfeng’s own classification is
based on function and form since a feature’s function determines its form, processing and assembling
demands [13]. Dinesh (1999) classifies form features under positive or negative form features [14].
These negative form features are equally known as machining features since they are obtained from
machining processes. They are mainly holes, slots, pockets etc. Also, geometrically, features can be
classified under regular shaped features and freeform features [15]. Features can equally be classified
into five groups with respect to the role they play in the system.
• Functional features which are those features relating to the principal function of the system in
question.
• Assembly features which can be defined as the features used in linking single components of
a product together [16]. Lee and Andrews (1995) define them as elementary relations
between components extended with some assembly information [17] while (De Fazio, 1990)
sees them as a collection of elementary relations matching form features [7]. Lastly, an
assembly feature can be seen simply as an association between two form features present on
different parts [18].
• Maintenance features which refer to those dispositions considered in a system to ensure its
maintainability [19].
• Safety features which should be dispositions that avoid or prevent damage to people, system
and environment.
• Manufacturing features which correspond to volumes in a product that could be machined
with a single or sequence of operations.
2.3 Modeling
Modeling is the representation of an object or non-objects in the form of a model for its
explanation [19]. It can equally be seen as the act of bringing out a representation of an object on a
smaller scale. Generally, the model can either be quantitative (mathematical) or qualitative. The
latter can be a representation of the prototype of a part or product. It can equally be a way of
representing an item for a better understanding. That is the modelling spoken of in this work.
A great deal of research has focused on modeling industrial engineering problems, over the
last fifty years, resulting in a wide variety of tools. These tools include linear programming, fuzzy

41
logic, artificial neural nets, Petri nets, Genetic Algorithm, features (manufacturing, assembling...),
etc.
2.4 Design and Feature based design
Design is a human activity where the physical artifact or a part of it, which is under design, is
not currently existent, but is believed to be so in the future [20]. The fact that the ultimate thing is not
currently physically existent and cannot be observed and manipulated makes it necessary to represent
the thing conceptually. Drogoul et al. (2007) define design as the process by which detailed
specifications sufficient for unambiguous production of an entity [21]. Ernst and Stanislav (2008)
give a more explicit definition of design: a process of formulating a description for an anticipated
process system and/or an object system that is intended to transform an existing situation into a
future situation to satisfy needs [22].
It has been found out that the environment is usually missing or not integrated in process
models at the design stage. This has led to research work on the integration of the environment in the
process model in which case the environment is represented using objects [20]. In this process safety
is enhanced since manufacture follows the model simulated with the environment. Nevertheless, only
an ideal environment can be modeled and as different risks show up in the existing process daily, it is
difficult to eliminate all the risks using this method.
Figure 2.1 illustrates the evolution of the deviations from nominal with the life of the system.
And Figure 2.2 shows better safety opportunities while designing [23] (Greenberg, 1991).
2.4 Integration of safety in design
Integration is a natural phenomenon, which raises the isolated activities to a higher level with
a new sense on the basis of which the functioning of the whole is more efficient and more intelligent.
Fadier and De la Garza (2006) state that there exist two safety integration methods [24]:
• The direct method, which operate through standards, and other formal documents, design
tools and actions. This is equally known as the explicit modality.
• The indirect method, which correspond to the implicit and individual modality and operate
through individual characteristics of each actor (knowledge, experience).
The last method incorporates the feedback from the user. Generally, safety is considered in
the design of any system via the first safety integration method. Nevertheless, errors do exist in the
design process and are only noticed at the exploitation stage. These errors and deviations occurred
are the causes of 20 to 60 percent of the accidents on installations [25]. These life cycle shortcomings
are first checked and some corrected during design review but a certain percentage still moves up to
be identified or not by the user. It should be noticed that a system’s development begins with design
and so design offers the earliest, and hopefully the cheapest place to intervene and get it right.
However, so many factors influence or shape the integration of safety in the design process. This is
because safety, to a certain extend is an intangible cost incurred in the design of a system.
As much as safety imposes additional requirements on the design that may add to costs and may lead
to decreased profit margins or even loss of market share to competitors with less safe but cheaper
design, the suffering and waste which can result from design errors and missed safety opportunities
can never be under looked. Safe design can thus be seen as a design that allows and conditions, as far
as feasible, safe use across the whole life cycle of the product. That is from manufacture,
construction, transportation and installation, through use, maintenance and modification, to
decommissioning, demolition and disposal.
Even though a standard design process exists, it does not guarantee an error free design. This
is because there is a gap between the designer’s view and the user’s view which equally needs to be

42
considered in the design process. Thus the design process needs to be both proactive (projecting new
designs into their future use situations) and reactive (feeding back experience of using earlier
designs) [25].
Figure 2.1: Evolution of the deviations from nominal with the safety integration in system
design
Figure 2.2: Effects of timing of design changes
3. METHODOLOGY
Concurrent Engineering (CE) has become the new norm in new product development across
the company worldwide, for organizing and managing all aspects of product process design and
development activity for their products. The approach enables the integrated development of
products and processes with the goal of completing the entire cycle in shorter time at lower overall
cost with fewer engineering changes. So very early in the product design process the approach
requires a multidisciplinary high level teamwork. That is functional disciplines such as, design,

43
manufacturing, assembling, maintenance, safety, marketing, etc. are involved. Obviously the design
object view and design language are specific and often contradictory for each discipline [19]. But at
the end common global language and view are to be achieved thanks to designers’ trade-off.
Disciplines features as means of communication must enable this purpose. Hence for safety features
modeling and their management in design process the figure 3.1 is illustrative for the methodology.
Figure 3.1: Methodology layout
The methodology presented in fig. 3 consists of two main steps which are modelling of safety
features and integration of safety in design.
Safety features exist but without a general or global nomenclature and classification. Thus,
this first step which is safety features modeling consists of defining, identifying the different safety
features, classifying them based on given criteria and finally characterizing them. This part will be
basically assembly and modification of what is in literature.
The next step which is the integration of safety in design consists of two parts:
• Representing the design process as a feedback process and analysing it. That is the process
from design through manufacture and installation to utilization.
• Establishing an algorithm for the integration of safety in design process. In other words
establishing a design procedure which considers reactive knowledge.
4. RESULTS AND DISCUSSION
4.1 Safety features Modeling
A safety feature is defined in this work as a group of characteristics or information relative to
the function, geometry, technology and other attributes of an object which enables it to eliminate or
reduce hazards, protect personnel, installations, products and/or environment from the hazard or
reduce the effects of any accident.

44
The different safety features identified are:
• Elimination safety features.
• Reduction safety features.
• Active protection safety features.
• Passive protection safety features.
• Safe Working procedures.
• Safety signs.
• Personal protective equipment (PPE).
• Emergency equipment.
To ease comprehension, the above identified features can be classified as seen on figure 4.1.
Generally, safety features can either be found incorporated in the equipment (machine) or out of the
equipment.
Figure 4.1 Safety features Taxonomy
Thus the two main classes of safety features are:
Safety features incorporated in machine which refers to the features found in the main structure of
the machine, incorporated with the components of the machine during installation or even attached to
the body of the machine. The features in this class are:
• Inherent safety features: These are features that are formed directly on the main body or are
joined inseparably to the machine. Thus these features eliminate or reduce the hazard and
keep the machine safe. These features are ranked higher in priority since they are intrinsic
and thus less costly and more effective.

45
• Add-on safety features: These are features which are only added to the main body of the
machine. They are equally known as protection safety features. These are features designed
to protect the workers, product, environment or machine from risk. Here, it is the occurrence
of the hazardous situation that is eliminated or reduced. These protective safety features can
either be passive (do not need any power source) e.g. guards, or active (need a power source)
e.g. fuses and relays or safety signs (which can either be regulatory (prohibition and
mandatory), warning (caution and danger) or information (emergency and general
information)).
Safety features out of the machine are those which are not directly linked to the operation of the
machine; are found neither in nor on the machine body and are not mounted directly onto an
incorporated component of the machine. The features in this class are:
• Emergency equipment which are used in cases of emergency. They include emergency stop
buttons and fire extinguishers.
• Safe working procedures are safety signs in that they do not ensure safety on their own. They
are step by step instructions on how to operate a machine for a particular purpose. They can
be procedures for the normal operation of the machine or for other aspects like their
installation and maintenance.
• Personal protective equipment are safety features used by personnel for their individual or
personal protection.
• Safety signs out of machine have the same function as the safety signs on the machine.
Characterization helps in giving a complete and technical description of the feature. The
characterization parameters proposed here are: function, shape or geometry, dimensions,
manufacturing technology, position, material, colour and the nature of the information.
• Function is the first and important point when it comes to feature characterisation because it
is from this other parameters emerge. It refers to what the feature is to do in order to enhance
safety. Generally, for inherent safety features, the function is to eliminate or reduce the
hazard. For add-on features to protect against the hazard. For the specific functions, it is left
to what precisely the feature does.
• Shape or geometry refers to the look or the outfit of the feature. The simplest arrangement
that permits the feature to accomplish its function effectively and is easy to manufacture. This
is in the case of form features that emerge to assembling features.
• Dimension refers to the sizes of the different measurable quantity. For the safety function to
be accomplished, a particular size of the feature is needed thus its dimensions characterise the
feature. For safety signs the size of the paper or plate should be conspicuous in order to draw
the attention of the personnel. Thus with respect to where and for whom the sign is for, the
size is determined.
• Manufacturing technology refers to the manufacturing sequence that is used to realise the
feature. Different technologies lead to different outputs especially in cases of precision. Thus
the technology used in the manufacture of a particular feature gives knowledge on aspects
like dimensional precision, strength, the nature of the surface etc.
• Position refers to where it is located on the structure. The description here is most at times
relative to other features. Two features can have the same shape and dimensions but their
position can change their function.

46
• Material refers to the internal make-up of the feature. The choice is made with respect to
other parameters regarding the material strength, availability, cost and equally what the
feature is to be used for.
• Colour is one of the aspects that characterises safety features. Different colours pass on
different messages. In some cases like in pipes, just the colour of the pipe is a safety feature
because it gives information on what is being transported in the pipe and thus the personnel
knows the safety precautions to take when in that zone. Active protective features have
peculiar colours to indicate their function.
• Nature of information is used for the characterization of safety signs and safe working
procedures. For safety features, generally the information can be exclusively signs or text or
mixed. On the other hand, safe working procedures can be in text form or can have
illustrative pictures or diagrams.
4.2 Safety Integration in design process
The feed-back process design illustrated in Figure 4.2 shows risk assessment at each step in
the process. But it seems to not be relevant because we don’t have no information about the reactive
Knowledge.
Figure 4.2: Representation of evolution of the feedback design process
4.3 Proposed algorithm for the integration of safety in design
As seen above, a machine passes through the design stage, is manufactured and installed
before it can be used.
This process starts with a study of design specifications occurred from the needs or the
existing non satisfactory equipment. This involves having a knowledge of the primary and secondary
functions of the equipment and there after its operation. It does not only end at the normal operation
but goes further to look at the installation and maintenance operations involved.
The next step consists of identifying already existing safety features and the risks they are
actually reducing. This in other words is bringing out the present state of the machine with respect to
System life
Design
stage
Manufacture
stage
Installation
stage
Utilisation
stage
Risk
assessment
Reactive
knowledge
Proactive
knowledge
System
performance+
+

47
safety. Note should be taken in this step since a risk reduction measure can be a hazard which should
be assessed in the next step.
The third step is risk assessment and this is a crucial stage since it is what gives the
information to be fed back into the design process. This is done, with the exemption of already
reduced risks. The aim of this assessment is to know the level of risk to which the equipment,
personnel and environment are exposed, this being the focal point. The risk assessment method
adopted will differ depending on the system in question and the available information. It will also
depend on the competence or how versed the user of the method is with the method. It should be
noted that since the concept of ‘zero risk’ is not real, acceptable risk is used as a reference in the
procedure except in cases where two or more acceptable risks which have the same source show up.
The question asked at this step is whether each risk identified and assessed is acceptable or not. If it
is acceptable, the design is maintained. On the other hand; if not, the designer goes to the next
question which aims at knowing if the risk can be eliminated or removed. If it can, the elimination
safety features modeling for that starts. On the contrary, if the hazard cannot be removed, a check to
know if it can be reduced is done. If the answer to risk reduction is yes, the modeling of risk
reduction features starts. If no, another check is carried out to know if there is a possibility of
protection. In the case of a positive answer, protective features modeling starts in which case it can
either be passive or active protective features with priority given to the passive safety features.
Regulatory signs can equally be used here. In the case of a negative answer, warning signs, safe
working procedures, personal protective equipment or training can are adopted. Hazard evaluation is
depicted in figure 4.3 while the integration algorithm of safety in design proposed in this work is
shown in figure 4.4. As far as safety is concern in the design process the modification leads the
modeling of safety features to eliminate, to reduce or protect the design system to danger at each step
of the process.
Figure 4.3: Hazard evaluation

48
5. CONCLUSION
Unsafe design
Safe design
Design
Utilisation
stage
Installation
stage
Manufac-
turing stage
Start
Study of equipment
operation
Identification of
existing safety features
Risk assesment
Safety signs, safe
working procedures,
PPE and training.
Equipment
operational?
Can hazard
be removed?
Acceptable
risk?
Can risk be
reduced?
Protection
possibility?
Inherent
safety
feature
Protection
feature
D
E
S
I
G
N
P
R
O
C
E
S
S
Maintain design
Feature modeling
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
Figure 4.4: Procedure for the integration of safety in design through the feedback
process

49
In this work, we presented how safety features can be defined, identified, classified and
characterised. To summarise, these features were classified based on their position and function. As
concerns their characterisation, it was done based on nine criteria which are function, shape,
dimensions, manufacturing technology, position, material, colour and the nature of the information.
We equally presented the design feedback process, which shows how reactive knowledge from the
user gets back to the designer for safety design amelioration. An algorithm was brought out to ease
the work of the designers as concerns the safety of the equipment. In perspective for safety
integration in design process to be relevant, mainly in CE (Concurrent engineering), a genuine safety
language is to be designed for communication with other disciplines designers.
5. REFERENCES
[1] Wong S. Y., “Automated Geometric feature Recognition – An essential Component for
Automated Design for Assembly”, M Phil Thesis, City Polytechnic of Hong Kong, 1992.
[2] Venuvinod P.K., Yuen C.F., “Efficient Automated Geometric Recognition Through Feature
Coding”, Annals of CIRP Vol. 43/1/1994, pp 413-416.
[3] Yuen C.F, Venuvinod P.K. “Geometric Feature Recognition: Coping with Complexity and
Infinite Variety of Features” International Journal of Computer Integrated Manufacturing,
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[4] Sinnott, R.K., 2005. “Coulson and Richardson’s Chemical Engineering, Volume 6”, Fourth
Edition, Chemical Engineering Design.
[5] MIL-STD-882D, 2000 “Department of defense standard practice for system safety”.
[6] Hale, A., Kirwan, B., Kjellén, U., 2007, “Safe by design: where are we now?” Safety
Science 45, pp 305–327.
[7] De Fazio T.L., 1990, “A prototype of feature-based design for assembly”, ASME advances in
Design Automation, Chicago, IL, USA.
[8] Dixon, J.R., Cunningham, J.J., Simmons, M.K., 1987, “Research in designing with features”
In H. Yoshikawa and D. Gossard, editors, Proceedings of IFIP TC5/WG5.2 Workshop on
Intelligent CAD.
[9] Motavalli, S., Cheraghi, S.H., Rafie, S., 1997, “Feature-Based Modeling; An Object Oriented
Approach”. Computer and industrial engineering, Vol 33. No.1-2, pp. 349-352.
[10] Nzie, W., 2002. « Modélisation des features pour l’intégration de la maintenance en
conception », 74p, Mémoire de DEA soutenu le 13 mai 2002 à l’UTBM, France.
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concepts and prospects” Computers in industry 49, pp 217-233.
[17] Winfried van Holland, Bronsvoort, W.F., 2000. “Assembly features in modeling and
planning”, Robotics and Computer Integrated Manufacturing 16, pp 277-294
[18] Lee, K., Andrews, G., 1985, “Inference of positions of components in an assembly: part 2”,
Computer-Aided Design.

50
[19] Nzié W. “Integration de la maintenance en conception: Application à un équipement Agro-
alimentaire”, these de Doctorat soutenue à l’UTBM, le 27 février 2006, France.
[20] Pohjola, V.J., 2003, “Fundamentals of safety conscious process design.” Safety Science 41,
pp 181–218.
[21] Drogoul, F., Kinnersly, S., Roelen, A., Kirwan, B., 2007, “Safety in design – Can one
industry learn from another?”, Safety Science 45, pp 129–153.
[22] Ernst, E.W., Stanislav, H., 2008 “Design engineering. A manual for enhanced creativity”
CRC press, Taylor and Francis group Boca Raton, London, New York.
[23] Greenberg, H. R. and J. J. Cramer. 1991. “Risk Assessment and Risk Management for the
Chemical Process Industry”. Van Nostrand Reinhold, New York.
[24] Fadier, E., De La Garza C., Didelot A., 2003, “Safe design and human activity: construction
of a theoretical framework from an analysis of a printing sector”, Safety Science 41,
pp 759–789.
[25] Fadier, E., De la Garza, C., 2006. “Safety design: Towards a new philosophy”, Safety
Science 44, pp 55–73.
[26] Sachin B. Bende and Nilesh P. Awate, “Design, Modeling and Analysis of Excavator Arm”,
International Journal of Design and Manufacturing Technology (IJDMT), Volume 4, Issue 2,
2013, pp. 14 - 20, ISSN Print: 0976 – 6995, ISSN Online: 0976 – 7002.

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