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IMPLEMENTING INHERENT SAFETY THROUGHOUT PROCESS

LIFECYCLE

Markku Hurme, Mostafizur Rahman

Helsinki University of Technology,

Laboratory of Plant Design, P.O. Box 6100, FIN-02015 HUT, Finland

markku.hurme@hut.fi

Abstract

Inherent safety should be implemented as early as possible in the design life cycle, since the

changes in process design are easier and cheaper the earlier they are done. The problem is, how

to evaluate process alternatives in the terms of inherent safety in the early design phases, when

much of the information is missing. In this paper the process life cycle phases, the inherent

safety analysis techniques used in them and the accuracy of methods is discussed.

1. Introduction

The aim of process design is to create a process that is economic, safe, and environmentally

benign throughout the whole lifetime of the plant. It is required that the safety of a process plantfulfils certain level because of general society requirements, company image and economic

reasons. An unsafe plant cannot be profitable due to potential losses of production and capital.

The safety of a chemical process can be achieved through inherent (internal) and external means.

The inherent safety is related to the intrinsic properties of the inherent safety to remove hazards

rather than to controlling them by added-on protective systems, whic is the principle of external

safety.

As a process goes through the phases of lifecycle, such as research and development,

design, construction, operation, modification, and finally decommissioning, inherent and added

on safety have a varying emphasis. The major decisions on process principle are done in the

process development and conceptual design phases. Therefore the process development and

conceptual design phases give the best opportunities of implementing inherent safety, whereasadded on safety has its applications in detailed process and plant engineering. In fact the

possibility of implementing inherent safety decreases as the design proceeds (Fig.1). Thus the

inherent safety characteristics should be evaluated systematically as early as possible to gain

larges benefit. However, the lack of detailed information especially in early design phases

complicates safety evaluations and decision making. At this point, much of the detailed

information - on which the decisions should be based - is still missing, because the process is not

yet designed. Once the process is designed, one would have all the information, but not the

freedom to make conceptual changes. This design paradox makes it necessary to implement a

dedicated methodology for estimating inherent safety in the early design phases to allow its early

adoption. This paper will discuss the principles of inherent safety implementation and evaluation

throughout the process lifecycle.

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Conceptual

Flowsheet

PID

Detailedeng.

Constrution

Startup

Operation

Research

Figure 1. The design paradox and inherently safer design

2. Evaluation of inherent safety

Most of the existing safety analysis methods have been focussed on existing plants or design

phases where all documents are already available, because they require detailed information

about equipment and plant layout. Safety aspects are however most effectively being considered

early in chemical process development. This is hindered by lack of knowledge of the process. At

the early stages, only quite limited information on equipment and plant layout exists. Thus, mostcommon methods intended for analysing full designs or plants in operation cannot be used. For

this purpose in inherent safety indices have been developed. They are based on the information

available in the early design phases.

The first index published for evaluating the inherent safety was the Prototype Index for

Inherent Safety (PIIS) by Edwards and Lawrence (1993). The Inherent Safety Index (ISI) by

Heikkil and Hurme (1996 and 1999) was developed to include more aspects than PIIS. The i-

Safe Index was developed by Palaniappan et al. (2002 and 2004). The indices use somewhat

different criteria to evaluate inherent safety and therefore have to some extent different data

requirements (Rahman et al. 2004a,b).

In this paper the problems of implementing inherent safety evaluations and their

accuracies in process lifecycle are discussed. For this purpose we have to look more closely,what are the lifecycle phases and how the amount of the knowledge on the process will increase

in design.

3. Process lifecycle phases

A process goes through various stages of evolution. Progression through these stages is typically

referred to as the process life cycle:

1. Idea

2. Research and development

3. Preliminary process design

4. Basic engineering

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Opportunities forinstallinginherently safer features

Knowledge of process

Opportunities forinstallingadd-on safety features

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Action

Product development

Process development

Process design

Plant concept

Detailed engineering

Construction

Aims and decisions

Research decision Design decision Investment decision Plant is ready for operation

5. Detailed engineering (Plant engineering)

6. Procurement, fabrication, construction, installation

7. Start up

8. Operations, maintenance

9. Modifications, retrofitting

10. Decommissioning

Many of the phases are separated by decision phases as shown in Figure 2.

Figure 2. Life cycle phases of a process in a development and design project

3.1 Idea phase

New ideas often deal with new or improved products and processes. The first check of the

viability of a new idea is often done quite quickly. If the idea looks promising in economic,

safety and environmental terms, preliminary research and development can be started by a

research decision (see Fig. 2). In idea phase information is collected on competing processes,

patent situation, legal aspects and environmental and safety considerations, as well as raw

materials, reaction chemistry and product specifications. Typical information available in this

phase on a new process is the main reaction chemistry and the basic physical, chemical and

toxicity properties of the compounds present (Figure 3). The methods used in safety analyzes

have to be based on these basic properties. The result of inherent safety estimation by index

methods is very rough and does not give a right ranking of process routes (Table 2).

3.2. Research and development phaseAs a new project is started, the chemical synthesis route is selected. The main goals are yield,

product quality and safety. To apply inherent safety, research chemists must make an in-depth

investigation on the process chemistry. Reaction hazards have to be investigated by reaction

calorimeter to find out the conditions, where possible side reactions take place and to find out the

possibilities of a runaway reaction.

After the definition of the chemistry, reaction conditions the basic concept of the future

process is defined. Research engineers have now many opportunities to incorporate inherent

safety principles in the choice of chemical synthesis route for example by:

1) implementing catalysts leading to less severe operating conditions

2) eliminating a hazardous solvent by using a safer one such as water

3) reducing reaction temperature, pressure and concentration4) using a more volatile solvent that refluxes and provides efficient cooling of reaction.

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After the process chemistry has been established, which defines the hazards of the materials,

process development personnel needs to focus primarily on process synthesis and unit operations

used. This includes the process scheme with reaction and separation steps. In this phase bench

and pilot experiments may be necessary for scale-up. Nowadays also mini plants are used to

allow continuous process testing in small scale.

In R&D phase, which includes also conceptual phase, the designer has the greatest opportunityto implement inherent safety principles, since most major decisions are done in this phase. Also

most inherent safety principles can be considered in conceptual design as shown by Kletz (1991)

in Table 1.

Table 1. Inherent safety principles considered in first project stages (Kletz, 1991)

Feature Conceptual stage Flowsheet stage PI-diagram stageIntensification X X

Substitution X X

Attenuation X X

Limitation of effects:

- By equipment design- By changing reaction conditions X X

X

Avoiding knock-on effects:-By layout

-In other ways

X X

X X

Making incorrect assembly impossible X

Making status clear X

Simplification X X

Tolerance X

Ease of control X X

Software X

Because many fundamental decisions are made, creative thinking is important in new processdevelopment and in looking opportunities to make the process more inherently safer. New

principles, such as process intensification, can systematically be implemented to reach the goal

(Rong et al., 2004).

In R&D phase inherent safety can be estimated quite well by using the Inherent Safety

Index, since most of the information needed is already available (Fig. 3). The accuracy of

evaluation is nearly as good as in the process predesign phase coming next. The ISI index can

give a quite reliable inherent safety ranking of the process alternatives as presented in the MMA

process case study (Table 2). In some cases ranking gave however same ranks to some quite

similar alternatives.

3.3 Preliminary process design

Preliminary engineering (or process predesign) is often done only for one process concept based

on a pre-feasibility study done earlier. Material and heat balances for the process concept are

calculated and flowsheet diagrams generated. For this purpose the type of unit operations have to

be decided, if not already done in process development. Preliminary sizing of main equipment

and a preliminary layout is also done. More accurate estimations of cost and profitability, safety

and environmental aspects are made in a feasibility study to find out, if the project is still

promising.

In process predesign the decisions are related to process dimensioning and unit operation

types. Even the operating conditions of key equipment are partly determined already in process

development, there are still good opportunities to implement inherent safety principles; see Table1: Intensification and simplification can be done further by using process intensification

methodologies (Rong et al., 2004). It may also be possible to substitute some chemicals with

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safer ones. Attenuation can be practised on temperature and pressure. Knock-on effects can be

limited by layout. Using smaller vessels and reducing need for intermediate storages can change

process inventories. This may however have a negative effect on controllability.

Plant location is analysed. It may be possible to reduce or eliminate transportation risk by

locating the plant, where hazardous raw materials or intermediates are produced, if the risk from

transporting the raw materials or intermediates outweights the risk of transporting the finalproduct. Locating plants at the same site will provide additional opportunities for risk reduction

by inventory reduction.

In inherent safety evaluation there are some new data is available for the ISI index;

equipment types, process structure and a more exact inventory. The accuracy of estimation is

however not much increased compared to conceptual phase in the MMA case study shown in

Table 2. Other methods available are a pre Hazop, which can be done by the designer as a

simplified form, and Dow F&I index, which can be applied to large extent even some

information is missing.

3.4 Basic engineering

A plant construction project starts with basic engineering. The main task is to make the PI-diagrams to AFD (accepted for design) phase and to complete all equipment process datasheets.

This means all process data for equipment is defined. Automation designers make the basic

definition of the automation system, which includes the number of instruments and controllers.

Facility designers make only a layout in this phase. Some companies require also that a Hazop

(hazard and operability study) is done already in this phase. Also a cost estimate and a project

plan for the design and construction project is done. In basic engineering no pipeline or

instrumentation design is made, neither equipment diagrams.

In basic engineering phase the normal operating conditions and the limits for safe

operation are defined. The key equipment is the chemical reactor. All their possible hazardous

situations should be covered and possibilities of them minimized. Means to deal with these

situations should be taken into account. The information defined in process design phase

determines the values for mechanical design. For example, the materials of construction of

equipment should be in accordance with process materials and also with all possible impurities

and trace elements. Because over half of the hazardous incidents are associated with start-ups,

shut-downs, maintenance work and abnormal operations, all the abnormal situations, including

start-ups and shut-downs, should be considered. Assessments can be done in different ways. A

commonly used method is a critical examination, especially the Hazop study.

In process design it is important to get the fundamentals right from the start. As the

design project proceeds, it becomes more and more expensive and difficult to change process

fundamentals. Earlier decisions may limit the options in the later design stages, but inherently

safer principles can still be applied. Basic design is the last step when changes can be made atmoderate cost. Once the facility is constructed the cost of modification usually increases notably.

The situation of implementing inherent safety principles is somewhat changed from the

previous design steps (see Table 1). The inherent safety aspects are now related to process

components such as process design aspects of equipment, piping and instrumentation. Inherent

safety indices cannot any more be applied to measure safety level but more detailed methods

such as Dow F&I index and Hazop studies can be applied.

3.5 Detailed engineering

The detailed design includes mechanical design of the equipment, piping, structural, civil

engineering and electric design and specification and a design of ancillary services. Also a

detailed layout is done. The key objective of the detailed design phase is to make documents anddrawings for construction, procurement and commissioning. However the plant cannot always

be engineered as the process engineers have designed. Therefore checking of piping, equipment

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and instrument design documentation has to be done by the process engineer. The differences

between process and detailed engineering documents have to be analysed and the effect on safety

studied. Small changes may change the process behaviour and ruin the inherently safer design

principles adopted. As an analysis method a complete Hazop study can now be done, since all

engineering documents are now available. However, making changes is expensive and can cause

delays and further errors. So no changes are welcomed in this phase.

3.6 Construction and start-up

The construction phase starts with preparation of foundations and buildings. When equipment is

installed, work continues with the installation of pipes, steel structures, electric devices and

instrumentation. From safety point of view the proper installations of equipment is necessary.

This is checked by inspection. The start-up phase begins with the testing of the facility. The

testing of the facility starts with water drives when all utility systems are operational and

instruments and control system are tested. It should be also ensured that process sequences

operate as they are planned. When the water drives have been fully completed, testing is carried

out with processing materials.

A key point in safety is the training given to operators. The training of workforce shouldbe started early before the start-up of the plant. They should understand the operation principle

of the process and automation system to be able to operate the plant in an inherently safer way.

3.7 Operations, maintenance and modifications

In addition to the safe operation and maintenance principles, which include proper training and a

work permit system, it is necessary that the inherently safer features, which are built into the

installation, must be documented and maintained. Often in process modifications these are not

understood or appreciated and changes are made, which change also the operation principle of

the process. Therefore the inherently safer aspects may be lost. In fact when making changes, we

should look for opportunities to make the system inherently safer and to reduce the risk level of

the process. This can be done based on the experience gained, i.e. there is a learning process

taking place during the plant operation.

In operation there are possibilities to human operating errors. Therefore the design should

be operating error tolerant. From this perspective, the chemistry of the process should be made

inherently safer by selecting materials that can better tolerate error in handling and charging.

Making systems easier to understand, operate, repair and assemble correctly can make the

process more inherently safer and more human error tolerant.

3.8 Decommissioning

Decommissioning means activities that take place after the normal production cycle and result

from recognition that a process has reached the end of its useful life time.The design and implementation of inherently safer chemical processes includes also a

consideration on the safety of dismantling of process equipment, reusing the site, and which

impact chemicals left behind in the plant or left in the soil or groundwater have at the plant site

or nearby. The process equipment and ancillary equipment must be removed or at least left in a

safe condition. There is a temptation to delay the cleanup of decommissioned plants as long as

possible. However, it is less expensive to do all the plant closure related activities immediately

after the plant is closed. This is also inherently safer.

A summary of tasks, information produced and safety tools available in various process lifecycle

phases is given as Appendix 1.

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4. Accuracy of inherent safety evaluations in process lifecycle phases of MMA processes

The Inherent Safety Index (ISI) developed by Heikkil and Hurme (1996, 1999) was tested in

three stages of process design lifecycle; in idea phase, R&D phase and predesign phase. The

information requirements of the ISI index for evaluating inherent safety are presented in Figure

3. In the idea phase there is typically available information on reactivity, flammability,explosiveness and toxicity of chemicals. In R&D phase there is available in addition to the

previously mentioned information also: heats of reaction, chemical interaction, corrosiveness,

yield, temperature, pressure. In process predesign phase in addition to the previous ones also:

inventory, type of equipment and process structure. Part of this information becomes gradually

more exact as shown in Figure 3 by dotted lines.

Idea phase R & D phase Predesign

Heat of reaction

Heat of side reaction

Chemical interaction

Flammability

Explosiveness

Toxicity

Corrosiveness

Inventory

Temperature

Pressure

Type of equipment

Process structure

Figure 3. Criteria used in the Inherent Safety Index and their availability in the test case

The testing was done by calculating the ISI index values for methyl methacrylate (MMA)

subprocesses and process routes in these three design steps by supposing the availability of

information described above. The process and index calculation principles are discussed byRahman et al. (2004a,b). The results were compared to expert evaluations presented by

Lawrence (1996). The results are shown in Table 2. It can be seen that the information available

in idea phase is not enough to rank process routes properly even the difference of subprocess

evaluations is quite small compared to expert evaluations. One explanation is that the experts

may have based their evaluations on component safety properties to a large extent, since they

were given only reaction equations, temperatures, pressures and the properties of chemicals

involved as the back ground information.

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Table 2. The difference between Inherent Safety Index -based and expert evaluations of MMA

processes in different design phases

Idea phase R&D phase Process predesign

Sub-process values 13% 11% 10%

Route values 7.0% 3.5% 3.4%

Route ranking 67% 0% *) 0% *)*) in some cases close routes give similar rankings

Conclusion

The paper has discussed the implementation of inherently safer design principles and the

evaluation of inherent safety in process lifecycle An inherently safer process development and

design involves iterative application of chemical engineering and inherent safety principles at

each decision point along the process life cycle. The key decision points from the inherent safety

point of view are: (1) synthesis route selection; (2) conceptual design; (3) flowsheet

development; (4) basic engineering and (5) later modifications. The major decisions on process

principle are done in the process development and conceptual design phases. Therefore the first

lifecycle phases give the best opportunities on implementing inherent safety principles. The most

crucial thing in process design concerning safety is getting the fundamentals right as early as

possible. As design project proceeds, it becomes more and more expensive and difficult to

change process fundamentals. Therefore a dedicated methodology, such as inherent safety

indices, to estimate inherent safety of conceptual alternatives is needed. It seems that inherent

safety can be evaluated quite well in the R&D phase involving conceptual design of the process.

A right inherent safety ranking of process alternatives was received in the MMA case study;

even there was not enough accuracy to rank some closely similar alternatives.

References

Edwards, D.W., Lawrence, D. (1993), Assessing The Inherent Safety of Chemical Process Routes: Is

There a Relation Between Plant Costs and Inherent Safety?, Trans IChemE, 71 Part B 252-258.

Heikkil, A.-M., Hurme, M., Jrvelinen, M. (1996), Safety Considerations in Process Synthesis,

Computers chem. Engng,20 S115-S120.

Heikkil, A.-M. (1999),Inherent Safety in Process Plant Design, D.Tech. Thesis, VTT Publications 384,

Technical Research Centre of Finland, Espoo; www.inf.vtt.fi/pdf/publications/1999/P384.pdf

Kletz, T.A. (1991),Plant Design for Safety: A User-Friendly Approach, Hemisphere, New York.

Lawrence, D. (1996), Quantifying Inherent Safety of Chemical Process Routes, Ph.D.Thesis,

Loughborough University of Technology.

Palaniappan, C., (2002) Expert System for Design of Inherently Safer Chemical Processes, M.Eng.

Thesis, National University of Singapore.

Palaniappan, C., Srinivasan, R., Tan, R. (2004), Selection of inherently safer process routes: a case study,

Chemical Engineering and Processing43 647-653.

Rahman, M., Heikkil, A.-M., Hurme, M. (2004a, Application of Inherent Safety Index to Process

Concept Evaluation, Loss Prevention and Safety Promotion in the Process Industries, Prague.

Rahman, M., Heikkil, A.-M., Hurme, M. (2004b), Comparison of Inherent Safety Indices In Process

Concept Evaluation, submitted toJournal of Loss Prevention in Process Industry

Rong, B.-G., Kolehmainen, E., Turunen, I., Hurme, M., Phenomena-based methodology for processintensification,Proceedings of European Symposium on Computer Aided Process Engineering-14,

Elsevier, Amsterdam 2004.

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Appendix 1. Tasks, information produced and safety tools available in process lifecycle phases

LC phase Tasks Information produced Suitable safety analysis tools

Idea phase - First check of feasibility oneconomics, and SHE

- first evaluation of

feasibility

- basic data on chemicals

Evaluation based on the basic

properties of chemicals

Process R&D - Reaction chemistry- Examination of raw materials

and reaction chemistry

- Process concept creation

- Examination competing

processes, patent and licensesituation

- Market analysis

- Examination of legal aspects- Laboratory & reaction

calorimeter tests

- Bench and pilot scale tests

- Prefeasibility study(profitability , SHE)

- chemicals and their

characteristics- chemical reactions

and interactions- thermodynamics

- physical properties- process concept

- first version of flowsheet- prefeasibility study

Laboratory screening and testing

-for chemicals (toxicity,instability, explosives)

-for reactions (explosiveness)-for impurities

Pilot plant tests

Inherent safety indices partly insimplified form.

Process

predesign

- Process concept selectionfrom alternatives

- Selection of unit operations- Flowsheet simulation

- Preliminary sizing ofequipment

- Analysis of logistics andmaterial flows

- Rough ISBL layout

- Estimations of emissions- Feasibility study

(profitability, SHE)

- flowsheet- material balance

- energy balance- process concept

- operating conditions- layout sketch

- feasibility study

Inherent safety indices.Dow F&E Index, Mond Index,

Hazop in simplified form.

Basic

engineering

- Process design of equipment

- Process design of pipes- Basic automation and

instrumentation engineering

- Layout design- Project planning

- PI-diagram (AFD)

- process data on equipment,piping and instruments

-

- preliminary layout- project plan

- detailed cost estimate

Hazop, Dow Indices, Mond Index,

Hazan, Fault tree, RISKAT

Detailedengineering

- Piping design- Instrumentation and

automation design- Mechanical design of the

equipment

- Structural and civilengineering

- Electric design

- Design of OSBL services.

- detailed engineering datafor equipment, piping,

controls, instruments,constructions

- layout

- operating, start-up andshut-down manuals

Hazop, Dow Indices, Mond Index,Fault tree

Procurement

FabricationConstruction

- Vendor and fabri-

cation documents- Inspection reports

- Field change documents

- vendor data on equipment- as built data

What-If, Checklist

Start-up - Start-up and test-run

documents

- data on processperformance

- first operation experience

What-If, Checklist

Operation - Operation reports - operation data- operation experiences

Hazop, Dow Indices, Mond Index,Fault tree, Operation fault analysis