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Failure types, consequences and possible remedies
ht. .I. Pres. Ves. & Piping 61 (1995) 199-21I
ElsevierScienceLimited Printedin NorthernIreland 0308-0161/95/$09.50
03080161(94)00105-7 ELSEVIER
FAILURE
TYPES,
CONSEQUENCES
AND POSSIBLE
REMEDIES
R K PENNY R K Penny & Associates Cape Town, South Africa
ABSTRACT
The main objective of the paper is to make suggestions An analysis of several types of engineering failures industry and the consequences of failures reveals that originate from human error. In particular, the design conceptual stages, materials selection and planning figures heavily in this. Some suggestions involving education and training are advanced as a basis for better
for
failure prevention. components and main sources of failure process involving early for reliable production new approaches for engineered products. by
INTRODUCTION
Failures of one sort or another are occurring every day, everywhere. Failures of political systems, social systems, economic systems and, of course interwoven with all this and more, engineering systems (Fig. 1). The resultant of all these failures is a highly negative one for all those who form a conglomerate which is loosely called “society”. As a partial cure for this state of chaos, there is a popular trend towards systems management through the electronic information technologies. As a means for analysing data faster, optimising the results of such analyses and for aids in decision making - the new technologies can be invaluable. But, there are two snags - at least, The first is that the wrong answers can be obtained and the wrong decisions can still be made, albeit faster, simply because the data needed is either the wrong data or it just isn’t available. The second snag, and it is a vital one, is that the new technology of information processing has an apparent sophistication in the eyes of young people. These people, our best resource, are being diverted from where they are most needed and that is in changing the magnitude and direction of the resultant vector of Figure 1. If the vector does not change, “society” will be for ever more in the hands of “after-the-event” people : medical technologists, lawyers, politicians and accountants. To cloud issues even more, another industry called “research” is also part of a process of diverting bright young people. The research syndrome is a realm of mythology in which its propagators firmly believe they are working beyond the limits of current knowledge, (Fig. 2) whereas practical applications are often already far beyond the limits of current knowledge (Fig. 31. This is where the brightest people are needed - with design as the driver of goal-oriented research. Those concerned with design will know very well that this is where meaningful research takes place. In view of these and other similar factors which are distorting the realities of need, it is not surprising that members of our communities are asking, for example, why it is that the heartbeat of a monkey in outer space can be monitored remotely whilst terra firma health care systems are so primitive. Whilst the political overtones of these viewpoints may seem obvious, the engineering implications are inextricably linked with political and other global systems. Take, for example, the generation, beneficiation and disposal
200
R. K. Penny
Public Service I ! (education, healthcare)
Unusual (probabilistic)
Representative
un-dependable,
Un-economic (counter-productive) The System (mis-government, mis-management) (codes, laws)
Services breakdown (illiteracy, environment deterioration, crime) Figure
1. The
Usual (deterministic) Failures
Vector
of materials - the Materials Cycle of Fig. 4. from 111, a UK Fellowship of Engineering report on new materials and innovation in manufacturing processes. It does not take too much imagination to realise that, at each and every step in the cycle, failures occur. Components degrade or break, systems shut down, people are injured or killed, production is lost and industries collapse. Some case studies in the materials producing and materials using sectors of Fig. 4 The global problem though is how to retard the come later in this Symposium. growth in the negative vector of Fig. 2, bearing in mind the increasing pressures on designers to aim for items which are cheaper, cost effective, and materials and which are environmentally less consumptive of energy friendly. All of this must be done under harsher and more complex conditions experienced by the designed item : loadings, speeds and temperatures principally.
Practical applicatio current Specialist’s view of current knowledge
Figure
2. State
of the
The purpose of this their causal features, remedial actions.
Art
- assumed
paper is to examine their consequences
Figure
Actual limits of current knowledge
Research
3. State
of the
Art
- as it
some generic types of failure and and some suggestions for possible
FAILURES
This
is too
broad
a subject
to
describe,
is
let
alone
analyse
in
any
worthwhile
Failure
sense, beyond 1. The Failure there is plenty
the general overview expressed by the “Failure Vector” of Vector appears to this writer to be growing in magnitude of evidence for this, some of which we shall address later.
Mining, chemical agricultural (and engineering
Materials
Fig. and
Civil, mechanical, aeronautical, electrical, nuclear engineering
bio-)
Materials
Bulk
producing
j
Process
materials M*1alr~C*m*nt Chl)MUU (liars*, Pap.r.cil.*l BrlcW
Smell~R.li”* ~~m”b,clu’ UP Raw
20
types
3
\
rfde;ialr
\
Figure
using
Process Fc.rCI~Shee., RDd~T”b(l Engineering
I
or use waste products
materials
Design.Manufacture Assemble I
I
4. The Materials
Cycle
Even if we look at a sub-set of the general overview, in terms of what has earlier been described as the “Materials Cycle” we are no nearer to being able to get to a stage where rational, causal analysis is possible. This trend continues even if we take sub-sets of the Materials Cycle such as some typical interactions between a) product-producing industries and b) service industry inputs to these producers, Fig. 5.
I
I
1
Figure
I
5. Product/Service
I
I
Industry
Interactions
R. K. Penny
202
A simplistic approach to this dilemma is to try to categorise some main types of industries, to isolate some common features if possible, and then attempt some analysis. For example, one form of classification could be by engineered hardware products: l
l
land-based products - civil : buildings, roads, bridges, mines, - industrial : process plant, manufacturing non land-based products - marine : tankers, cargo ships, . . . . - aerospace : aircraft, space craft
transport, ... . plant, . . . .
Having reached this stage it is possible to attempt further analyses of engineering failures in terms of generic types of failures which are known to be involved within the product categories, the causes of these failures and the costs and any other consequential effects arising from the failures. Not all of the categories mentioned can be analysed within the confines of this short paper but some main themes and their importance in reducing the inexorable growth in the Failure Vector can be examined. In order to make reasonable progress towards these goals within this paper, particular examples mainly drawn from personal experiences within the manufacturing and aircraft industries will be used. Some
types
of failures
The failures to be described arise within two broad categories of activity : materials development on the one hand and specific failure analyses over a period of 20 years on the other. All are actual cases which can only be described briefly here. il A new material for aero-engines The idea for this material came from a young technician with a lot of common sense and initiative and little in the way of formal technical education. The material was needed for turbine blades which would enable higher temperature operation and thereby greater efficiency and in turn provide a major lead over other companies in the field. The idea was to cast blades such that its crystalline structure was aligned with the primary forces acting on the blade, i.e. axially. This object was achieved and the material concerned had higher toughness and ductility and better creep resistance ; the chemistry of the material was the same as for cast blades having random grain structures. Blades were made in the new material and these replaced old blades in a test engine. The engine tried to shake itself to pieces during testing. Reason: the stiffness of the directionally solidif ied material was different from the conventional material. As a result, the vibrational characteristic of the rotor/blade assembly had frequencies out of phase with those of other assemblies within the total makeup of the engine. ii)
Castings A company was to produce castings for certain motor car components. Because the components were part of a control system, the castings had to be near defect free. The company imported a casting system from Germany where similar parts were being produced to the same tolerances and with the same materials and quality as were required by the local company. The local company produced the parts with a batch minimum rejection rate of
203
Failure types
30% ; in Germany
the rate
was less than
1%.
Reason: the local company had poorly trained operators control methods were also incapable of discriminating 20% of the parts should not have been rejected. iii)
whilst the quality defects reliably ;
High temperature materials data collection These materials are said to have degrees of scatter in their rupture and strain accumulating characteristics. These uncertainties complicate the design process even more than it already is and, as a result, higher “safety” factors than should be necessary are used. Data collection is expensive in time, money and space so that an investigation was performed to reveal which factors were of primary importance. The investigation proved beyond reasonable doubt that for thermally stable materials of the types under investigation, the scatter of results was not high. Reason: the testing procedures were crude and inappropriate for being formed. Non-axial alignment of specimens, shock loading temperature control caused most of the scatter, not variability material.
iv)
the tests and poor of the
Miscellaneous, everyday failures Over a period of 20 years, 350 investigations of failed parts had been performed by a university department El. The selection of parts does not provide a random sample of failures in general ; in particular, there was a bias towards incidents which could have led to disputes as to liability. However, the causes of failure were clearly established. Table
1 sets out the occurrences
Total Part
of failures
number
of
failures
involved
:
Number
Boiler plant Bolts and studs Constructi on Hoisting tackle Tools Vehicles Miscellaneous plant*
* Chemical plant, systems . . .I, marine
general engines TABLE
Table 2 gives of categories.
a summary
44 13 7 44 16 50 176
engineering and ships. 1 Failure
of the
350
(pumps,
presses,
heating
occurrences
causes
of failure
within
a consistent
set
204
1 I
R. K. Penny
I
Part
0 igin Fab. Erect
of F,ai lure or Heat Treat. ion
Design
Faulty vlaterial
4 1
4 1
4 2
2
3
9
9
13 2 4
4
7 5 13
57
24
32
27
Boiler plant Bolts & studs Hoisting tackle Tools Vehicles Miscellaneous plant
TABLE
Reasons: al by activity,
Table
2 Failure
OP. lilaint.
Origins
Total Number If Parts
30 9
44 13
12 9 20
44 16 50
36
176
3 % total
Design Material faulty Product ion Use/misuse TABLE
b) by major
cause*,
22 14 31 33
3. Sources
Table
of
error
4 Number
Brittle
fracture
* most
common
TABLE
4 Types
Some of the conclusions drawn summarised as follows: Human error is involved at to production. l
l
l
l
Some
The and
% total
categories of
from all
error
these stages
small from
experiences data
collection
Operational errors and faulty maintenance also appear major source for failures arising from human error. This points driver of dependability
to the need for a new breed of a design/materials/production/maintenance as his system lifetime mission.
Failures arising those of sudden
consequences
from failure.
time
dependent
degradation
design
can
be
through
to represent
a
engineer as the cycle with
processes
outweigh
of failures
consequences of failures One financial terms.
are obviously of the main
numerous aims of
and this
often tragic in human paper though is to
205
Failure types
contribute to any ideas and other motivations towards failure prevention. It seems likely therefore that numerate approaches to financial implications rather than human ones could be more successful as possible persuaders for action. Cynical as this may be, it appears to be more appealing to the modern rhetoric of politicians and other major decision makers. At the same time, if successful, the altruism of sociologists and other caring people left out of the decisions arena would also be satisfied. There are two major “after-the-event” features of failures which can be analysed numerately. The first is an indirect one - litigation involved in loss or other liability claims. The second is direct - loss of productive plant. i)
Costs of litigation and their effects. Some statistics on tort costs and trends are available for the USA 131. Amongst these are . tort costs linked with product failures are high worldwide. In the USA an aggregate estimate for 1987 is about 2.5% of Gross National Product. This is between 3 times that of Switzerland and 6 times that of Japan. l
before growth. growing
World War II GNP was growing After World War II this trend at a compound rate of 12%.
at faster has reversed.
rates Tort
than costs
tort are
.
over a period of 12 years up to 1986 the rate liability cases is three times higher than cases in the private and Federal sectors.
.
since 1977 the accident rate in general aviation has continuously reduced. In spite of this, the cost of accident claims has risen seven-fold during the same period. As a result, a whole industry has been wiped out in the USA. These are all highly negative features in terms of the Failures Vector of Fig. 1. Although these features are for the USA, it is not difficult to speculate that the rest of the world will follow suit if strong, affirmatively driven action is not taken on a vast scale. One positive feature of the American statistics is an overall steady decline in workers injury and death rates: . in a forty year period since 1946 the death rate of workers from accidents has declined from 33 per million to 5 per million. The figures are 40 per 1,000 to 12 per thousand for in juries. during the same period the number of workers has increased from 40 to 120 millions.
of growth non-product
of
product liability
l
An inference which could be drawn from these sparse statistics is that whilst the law profession has created a huge business called litigation, the engineering profession remains impotent in spite of the fact that accident fatalities and injuries have dramatically reduced. Failures will still continue and whilst the vector may change even further towards “after-events” its could magnitude grow inexorably as operating conditions and other demands become harsher. ii)
Economic effects of failures An approach taken by Faria [41 towards failures is to restrict investigations fracture, corrosion and wear. This is the analysis in earlier parts of this
analysing the economic effects of to failures mainly caused by in accord also with the results of paper. Faria’s investigations were
206
R. K. Penny
focussed on the USA and Europe, categorised according to various parameters. Amongst these were industrial sectors, direct costs of fracture and the ways and means and costs of effective fracture prevention. Some of the most significant features are For the USA a) . across 154 industrial sectors involved in the production of articles ranging from aircraft to process plant using mainly metallic materials, the cost of failures by fracture was 4% of the USA GNP. On 1982 values of the USA dollar, this is approximately $120 billion, judged to be accurate to 210% 151. .
b)
a similar concluded
investigation of the economic effects of that the USA lost about 4% of its GNP [61.
corrosion
For Europe The objectives of European studies were much the same as those of the USA ; to provide economic evaluations of the effects of fracture and of erosion and wear for each type of equipment used within different sectors of industry. Similar conclusions were reached: losses due to fracture to 12 European countries belonging to the EC amounted to about 4% of the global GNP, judged to be accurate to f 25% [71. l
l
.
the losses due to the effects of British and German investigations those countries. earlier losses, studies,
erosion amount
reports with similar objectives lead to similar conclusions to i.e. about 4% of GNP.
and wear according to 2% of the GNP
insofar those of
as the
to of
corrosion American
These estimates show that the costs of advanced nations on account of failures caused by fracture, erosion, corrosion and wear can amount to about 10% of GNP (roughly 5 x 10” ECU). According to Faria 141, if indirect and consequential costs are accounted for the influence of fracture alone, on the total cost of products, can be as high as 25% (for heavy equipment with high costs) and 2% (for medium size, consequential light equipment with low consequential costs). He also refers to some cases where the total cost incurred by fracture failures attained 100% and more of the product costs ; the products were not specified. Causal
factors
of
failures
Taking into account the American and European studies described together with information from insurance companies, attributable to failures by fracture were categorised as follows .
. . . .
design faulty material manufacture and assembly use/misuse unknown
15% 5%
(22%) (14%)
25% 45% 10%
(31%) (33%)
briefly some
factors
The bracketed figures are taken from Table 3 above for comparative purposes. Considering that the sample size, types of product and date (1969) over which the comparative figures were obtained, the same trends appear in the larger
Failure types
sample which contains a wider range of industries and more recent information (19911. There seems to be little doubt that factors involving major human inputs : design, operation and maintenance, figure too highly at an estimated 60% (55%) in the failure samples. To this has to be added further human fault possibilities during manufacture and assembly. If this is the case for advanced nations, what is the state of developing countries where technology transfer is bound to give room for even greater human error? This is not necessarily because the skills gap is so large (even though it usually is) but for a multitude of other reasons, not least of which is communication. A simple example at the consumer level is with product instructions. A product has passed all its tests in, say, an Eastern European country, is packaged beautifully and sent off, say, to Malawi. The purchaser hires his plumber or electrician, say, to install the item. The tradesman cannot read the installation instructions, gets on with the job as best he can, tests the system and it appears to work. The owner uses the item for the first time and it explodes ; the tradesman did not set the over-pressure cut-out device Of course, such an event should have been according to instructions. anticipated by the designer anyway, but it wasn’t. It seems clear that there is an urgent need for an emphasis on education and training schemes aimed primarily at producing more people who are capable and the of holistic approaches to engineering design manufacturing technologies. The notion of an educated person being a scholarly individual who has been neither educated nor trained in the exercise of useful skills is no longer acceptable. The present imbalance between acquisition of knowledge with use of it in ways which are relevant and in ways which are relevant outside the education system has to be weighed in the reverse order of the present day and those of the cloisters. As was remarked earlier, the challenges of design are far greater than those of research without goal commitment. In this respect, many of the advanced (technological1 countries are not keeping up with the needs of “society”. The Failures Vector is mainly dependent on one resource - the human one. SOME
REMEDIAL
ACTIONS
The human resource is an enormous one which is virtually untapped and a badly educated and trained one. These are strong words but the Failures Vector tells the story. How can it be that the Crystal Palace, which covered 19 acres of space in London and was built in 17 weeks for the 1850 World’s Fair, operated without accident for many decades until it was burned down, whereas walkways in the Hyatt Regency Hotel collapsed within weeks of opening a few years ago in Kansas City, with disastrous consequences? In the latter case, simple design features which led to the failure were not checked by calculation or test. On the insistence of Queen Victoria, walkways and galleries of the Crystal Palace were tested in spite of there also being calculations to check its innovative design principles. The Hyatt hotel building was not an advanced or construction method but the designers did not one in its architecture anticipate possibilities for collapse. The Palace Crystal pre-dated skyscrapers and was unique at the time for its type and lightness of construction with ingenious structural forms to combat wind resistance. The designers successfully anticipated possible failure characters and tested for them. Easy in retrospect to make comparisons, but that such catastrophes as we witness today which, with a little help, undergraduates should be able to assess is worrying. All the more so that a couple of mechanics - the Wright discovered relevant brothers - successfully laws of aerodynamics, designed their structures, tested them and then flew them. Exceptional people undoubtedly, but it is unlikely today that mechanics would get so far even if
R. K. Penny
208
they did have the ambition. Are such people around today? some statistics based upon IQ testing, for what it is worth, are available for various groups of people as follows 191: Specialty
IQ Range
Ph. D Engineer Draughtsman Production Manager Clerk Lathe Operator Weaver Labourer
loo-169 100-151 74-155 82-153 68-155 64-147 26-145 26-145
Mean
IQ
130 127 122 118 118 108 97 96
These data show that there are few dull Ph.Ds but there are many bright and very bright weavers, . clerks and labourers. (In fact, three times as many labourers as Ph.Ds have IQs over 130, because there are so many more labourersl. In general, the mean difference between any two. groups on any dimension is not as great as we sometimes like to believe and the spread and overlap are very great. Of course, it takes many other characteristics than the IQ to find more like the Wright brothers. The resource is available though. How can we best benefit from its potential? Some suggestions follow. Practice
directed
learning
Much has been said and written over the last few decades about improving human reliability in engineering as a means for reducing product unreliability and failure. Most of these discussions have centred around ways and means for rectifying what is - for example, improving the knowledge of production engineers and their respect for quality or for better ergonomic design. There has been much debate about the “image” of an engineer held by the general public. Even more debate has swung various education pendula from science to applied science to engineering science in order to gain a more visible “image” but that has not worked in anybody’s favour. Injections of engineering design into undergraduate courses are often given, under protest, by academics who have never practiced engineering. A major result, of little benefit to anybody, is the creation of design “science” an apparently new subject which would otherwise be called system engineering. Finally, calls for management science have sometimes won over curricula planners to add a part course on the subject to engineering course ; and then a bit of economics and so on. It is surprising that engineers have rarely approached the job of engineering curriculum planning in ways that they design hardware and software. There are notable exceptions to this generalisation, of course, and the efforts of A Rosenstein and M Tribus and of J Dixon, for example, in the USA and of W Betz and M Pahl in Germany are all well known. A recent major analysis 181 has built on the efforts of Rosenstein, Tribus and Dixon with a view to helping in the development of young engineers who can exercise their creative skills in cooperation with others ; who have the capability to initiate, undertake and complete tasks on time and within set budgets ; who have the ability to work within and contribute successfully to everyday life. Readers of this paper may well ask “what has this got to do with failure prevention?” The answer is, not much, in the near future, but the essence is that the attitudes needed in the drive towards good engineering - which includes failure prevention - would be more successfully inculcated than in present schemes of education and training. Present attitudes of young graduates are too often geared towards nicely packaged, pre-digested/stated
209
Failure types
- the easy part problems as a lead in to analysis particulate way rather holistically. The analysis performed in 181 is based upon the graduates should be required to fulfil in satisfying that employers have of them. .
l
.
.
engineering
-
in
a
following premises that the valid expectations
remedying weaknesses in primary and secondary requires a better motivation towards engineering, basic subjects and basic skills and improving working
school the habits
education. underpinning
This of
giving students an image of engineers in industry. Industrial companies are the caretakers of technology as users and developers. Engineers in those companies must be seen as professionals, capable of playing an effective part with others in wealth-creating activities. ” . . . . not just interested in making cars but making money-making cars . . . . ” recognising that a major engineer is communication providing attitudes workplace
l
of
ensuring reliability, technical
time
consumer
in
the
life
of
a professional
a balanced curriculum which encourages and develops towards the engineering profession and to industry
development thoroughness astuteness
Laws
of
the and
personal attributes social concern as
store of Scientific
of Learning
of well
as
Knowledge
positive as a
pragmatism, those of
J
Speedof Scientific
Advances
Future wxds of an Exploding l’opulation
Academic
Increasing complexity New Systems
Traditions
Figure
6. Curriculum
of
Constraints
The analysis was then performed by examining the most obvious constraints which focus on curriculum design (Fig. 61. Course architecture (Fig. 71 was then relatively easy and from this, detailed design also followed. The course architecture is unusual in some important respects:
R. K. Penny
210 .
.
l
l
l
inputs to it are carefully screened and selected (just as a designer screens and selects materials for any job in hand). The screening uses available tools for personal aptitude testing a two year (40 week year) Foundation continuum provides for and assesses student potential for technician and engineering work. This continuum is a common one and contains no specialist options further selection by two stages is designed with a view to some specialism preferences which are served through a project basis. This is the Initial Formation stage where two pathways for graduation are provided and in which the designer/materials/production interactions are portrayed graduation at any stage is accompanied by programmes of continuing education and training the basis throughout is one of practice directed education in which the laboratories are factories and other everyday workplaces
A 3 E 1 E c T
C A T
T
CHOSEN TOPIC
MENTOR SYSTEM
0 N
0
COUNSELLING
Figure Other
FO”p
PROJECT ENGINEERING
s
P P L
0 N
Fa YEAR
remedial
COUNSELLING
7. Course
Architecture
actions
Cultivation of the attitudes of the human resource is a major task which has to be undertaken as a matter of urgency. However, the products of schemes such as practice directed education will take time to be of any measurable effect on the Failures Vector. Much cooperation on an international basis is vital and the costs are negligible compared with those of continued failures as has been demonstrated by Faria 141 The main stumbling block will be a human one the educators. The reason for this is that the educators, being human, believe that what was right for them as students must be right for their students. The research syndrome which has grown into the engineering streams of a modern university and out of a respect for science and discovery will also be hard to overcome in spite of the high cost and low productivity of university research. Private initiative to overcome these obstacles will have to be led by industry whilst governments seem hell-bent on perpetuating present systems of education and training. Whether or not the new breed of human engineering resource is generated,
211
Failure types
there are secondary, but vitally important help reduce the Failures Vector magnitude. .
inputs, being Some of them
made are
in other
ways
to
codes of practice and design rules. Good contemporary examples here are the well-known ASME guidelines for pressure vessel design and the lesser known Nuclear Power p. l.c. (UK) guidelines 1101 for high temperature designs containing defects guidelines on risk issues which set out different risk factors and their These are interactions, as well as suggested implementation actions. essentially awareness guidelines as aids to professional responsibility and an example from the UK has been published recently Ill] goal-directed research and results dissemination with particular reference to fracture problem solving. A good example is the creation of ESIS (European Structural Integrity Society) through the initiatives of the European Joint Research Centre of Petten, Holland 141.
l
l
CONCLUDING REMARKS Growth in what has been termed the Failures Vector is costing enormous losses in financial, economic, human and any other terms. The causes for this are largely of human origin. Whilst guidelines by way of codes of practice and other means are being devised and disseminated by authoritative bodies on an international basis, it is essential that new schemes for preparing young people for careers in engineering are designed and implemented as quickly as possible. These are most likely to succeed if they are propelled by private initiatives backed by industry and if they are practice orientated.
ACKNOWLEDGEMENT Figures
2 and 3 by courtesy
of D L Marriott.
REFERENCES 1. 2. 3. 4.
5. 6. 7. 8. 9. 10. 11.
“Modern Materials in Manufacturing Industry” Report by the UK Fellowship of Engineering at the request of the Dept. of Industry 0 1983 R K Penny. “Some Aspects of Design”, Liverpool Engineering Society Journal, vol. XCV, 5, July 1969. B Ross. Failure Analysis Associates, California, USA. Personal communication. L Faria. “Economic Effects of Failures of Systems”, International Conference on Structural Failure and Product Liability, Vienna, November 1993, Proceedings to appear. “Economic Effects of Fracture in the United States”, US Dept. of Commerce, Nat. Bur. Stand. Special Publ. 647-l & 2, March 1983. E D Verink, “Corrosion Economic Calculations”, Metals Handbook, vol. 13 Corrosion, ASM International, Ohio, 1987. “Economic Effects of Fracture in Europe - Final Report”. Commission of the European Communities, 1991. “An Opportunity for a New Initiative”. 0 Engineering Formation cc., Cape Town, 1993. A D Swain. “Improving Human Performance”, In Corn. Tee. Training Services, Camberley UK, 1974. R5 and R6 Procedures, 0 Nuclear Power p.l.c., 1991. “Engineers and Risk Issues”. Q The Engineering Council, ISBN 0-95166117-5, 1993.
ElsevierScienceLimited Printedin NorthernIreland 0308-0161/95/$09.50
03080161(94)00105-7 ELSEVIER
FAILURE
TYPES,
CONSEQUENCES
AND POSSIBLE
REMEDIES
R K PENNY R K Penny & Associates Cape Town, South Africa
ABSTRACT
The main objective of the paper is to make suggestions An analysis of several types of engineering failures industry and the consequences of failures reveals that originate from human error. In particular, the design conceptual stages, materials selection and planning figures heavily in this. Some suggestions involving education and training are advanced as a basis for better
for
failure prevention. components and main sources of failure process involving early for reliable production new approaches for engineered products. by
INTRODUCTION
Failures of one sort or another are occurring every day, everywhere. Failures of political systems, social systems, economic systems and, of course interwoven with all this and more, engineering systems (Fig. 1). The resultant of all these failures is a highly negative one for all those who form a conglomerate which is loosely called “society”. As a partial cure for this state of chaos, there is a popular trend towards systems management through the electronic information technologies. As a means for analysing data faster, optimising the results of such analyses and for aids in decision making - the new technologies can be invaluable. But, there are two snags - at least, The first is that the wrong answers can be obtained and the wrong decisions can still be made, albeit faster, simply because the data needed is either the wrong data or it just isn’t available. The second snag, and it is a vital one, is that the new technology of information processing has an apparent sophistication in the eyes of young people. These people, our best resource, are being diverted from where they are most needed and that is in changing the magnitude and direction of the resultant vector of Figure 1. If the vector does not change, “society” will be for ever more in the hands of “after-the-event” people : medical technologists, lawyers, politicians and accountants. To cloud issues even more, another industry called “research” is also part of a process of diverting bright young people. The research syndrome is a realm of mythology in which its propagators firmly believe they are working beyond the limits of current knowledge, (Fig. 2) whereas practical applications are often already far beyond the limits of current knowledge (Fig. 31. This is where the brightest people are needed - with design as the driver of goal-oriented research. Those concerned with design will know very well that this is where meaningful research takes place. In view of these and other similar factors which are distorting the realities of need, it is not surprising that members of our communities are asking, for example, why it is that the heartbeat of a monkey in outer space can be monitored remotely whilst terra firma health care systems are so primitive. Whilst the political overtones of these viewpoints may seem obvious, the engineering implications are inextricably linked with political and other global systems. Take, for example, the generation, beneficiation and disposal
200
R. K. Penny
Public Service I ! (education, healthcare)
Unusual (probabilistic)
Representative
un-dependable,
Un-economic (counter-productive) The System (mis-government, mis-management) (codes, laws)
Services breakdown (illiteracy, environment deterioration, crime) Figure
1. The
Usual (deterministic) Failures
Vector
of materials - the Materials Cycle of Fig. 4. from 111, a UK Fellowship of Engineering report on new materials and innovation in manufacturing processes. It does not take too much imagination to realise that, at each and every step in the cycle, failures occur. Components degrade or break, systems shut down, people are injured or killed, production is lost and industries collapse. Some case studies in the materials producing and materials using sectors of Fig. 4 The global problem though is how to retard the come later in this Symposium. growth in the negative vector of Fig. 2, bearing in mind the increasing pressures on designers to aim for items which are cheaper, cost effective, and materials and which are environmentally less consumptive of energy friendly. All of this must be done under harsher and more complex conditions experienced by the designed item : loadings, speeds and temperatures principally.
Practical applicatio current Specialist’s view of current knowledge
Figure
2. State
of the
The purpose of this their causal features, remedial actions.
Art
- assumed
paper is to examine their consequences
Figure
Actual limits of current knowledge
Research
3. State
of the
Art
- as it
some generic types of failure and and some suggestions for possible
FAILURES
This
is too
broad
a subject
to
describe,
is
let
alone
analyse
in
any
worthwhile
Failure
sense, beyond 1. The Failure there is plenty
the general overview expressed by the “Failure Vector” of Vector appears to this writer to be growing in magnitude of evidence for this, some of which we shall address later.
Mining, chemical agricultural (and engineering
Materials
Fig. and
Civil, mechanical, aeronautical, electrical, nuclear engineering
bio-)
Materials
Bulk
producing
j
Process
materials M*1alr~C*m*nt Chl)MUU (liars*, Pap.r.cil.*l BrlcW
Smell~R.li”* ~~m”b,clu’ UP Raw
20
types
3
\
rfde;ialr
\
Figure
using
Process Fc.rCI~Shee., RDd~T”b(l Engineering
I
or use waste products
materials
Design.Manufacture Assemble I
I
4. The Materials
Cycle
Even if we look at a sub-set of the general overview, in terms of what has earlier been described as the “Materials Cycle” we are no nearer to being able to get to a stage where rational, causal analysis is possible. This trend continues even if we take sub-sets of the Materials Cycle such as some typical interactions between a) product-producing industries and b) service industry inputs to these producers, Fig. 5.
I
I
1
Figure
I
5. Product/Service
I
I
Industry
Interactions
R. K. Penny
202
A simplistic approach to this dilemma is to try to categorise some main types of industries, to isolate some common features if possible, and then attempt some analysis. For example, one form of classification could be by engineered hardware products: l
l
land-based products - civil : buildings, roads, bridges, mines, - industrial : process plant, manufacturing non land-based products - marine : tankers, cargo ships, . . . . - aerospace : aircraft, space craft
transport, ... . plant, . . . .
Having reached this stage it is possible to attempt further analyses of engineering failures in terms of generic types of failures which are known to be involved within the product categories, the causes of these failures and the costs and any other consequential effects arising from the failures. Not all of the categories mentioned can be analysed within the confines of this short paper but some main themes and their importance in reducing the inexorable growth in the Failure Vector can be examined. In order to make reasonable progress towards these goals within this paper, particular examples mainly drawn from personal experiences within the manufacturing and aircraft industries will be used. Some
types
of failures
The failures to be described arise within two broad categories of activity : materials development on the one hand and specific failure analyses over a period of 20 years on the other. All are actual cases which can only be described briefly here. il A new material for aero-engines The idea for this material came from a young technician with a lot of common sense and initiative and little in the way of formal technical education. The material was needed for turbine blades which would enable higher temperature operation and thereby greater efficiency and in turn provide a major lead over other companies in the field. The idea was to cast blades such that its crystalline structure was aligned with the primary forces acting on the blade, i.e. axially. This object was achieved and the material concerned had higher toughness and ductility and better creep resistance ; the chemistry of the material was the same as for cast blades having random grain structures. Blades were made in the new material and these replaced old blades in a test engine. The engine tried to shake itself to pieces during testing. Reason: the stiffness of the directionally solidif ied material was different from the conventional material. As a result, the vibrational characteristic of the rotor/blade assembly had frequencies out of phase with those of other assemblies within the total makeup of the engine. ii)
Castings A company was to produce castings for certain motor car components. Because the components were part of a control system, the castings had to be near defect free. The company imported a casting system from Germany where similar parts were being produced to the same tolerances and with the same materials and quality as were required by the local company. The local company produced the parts with a batch minimum rejection rate of
203
Failure types
30% ; in Germany
the rate
was less than
1%.
Reason: the local company had poorly trained operators control methods were also incapable of discriminating 20% of the parts should not have been rejected. iii)
whilst the quality defects reliably ;
High temperature materials data collection These materials are said to have degrees of scatter in their rupture and strain accumulating characteristics. These uncertainties complicate the design process even more than it already is and, as a result, higher “safety” factors than should be necessary are used. Data collection is expensive in time, money and space so that an investigation was performed to reveal which factors were of primary importance. The investigation proved beyond reasonable doubt that for thermally stable materials of the types under investigation, the scatter of results was not high. Reason: the testing procedures were crude and inappropriate for being formed. Non-axial alignment of specimens, shock loading temperature control caused most of the scatter, not variability material.
iv)
the tests and poor of the
Miscellaneous, everyday failures Over a period of 20 years, 350 investigations of failed parts had been performed by a university department El. The selection of parts does not provide a random sample of failures in general ; in particular, there was a bias towards incidents which could have led to disputes as to liability. However, the causes of failure were clearly established. Table
1 sets out the occurrences
Total Part
of failures
number
of
failures
involved
:
Number
Boiler plant Bolts and studs Constructi on Hoisting tackle Tools Vehicles Miscellaneous plant*
* Chemical plant, systems . . .I, marine
general engines TABLE
Table 2 gives of categories.
a summary
44 13 7 44 16 50 176
engineering and ships. 1 Failure
of the
350
(pumps,
presses,
heating
occurrences
causes
of failure
within
a consistent
set
204
1 I
R. K. Penny
I
Part
0 igin Fab. Erect
of F,ai lure or Heat Treat. ion
Design
Faulty vlaterial
4 1
4 1
4 2
2
3
9
9
13 2 4
4
7 5 13
57
24
32
27
Boiler plant Bolts & studs Hoisting tackle Tools Vehicles Miscellaneous plant
TABLE
Reasons: al by activity,
Table
2 Failure
OP. lilaint.
Origins
Total Number If Parts
30 9
44 13
12 9 20
44 16 50
36
176
3 % total
Design Material faulty Product ion Use/misuse TABLE
b) by major
cause*,
22 14 31 33
3. Sources
Table
of
error
4 Number
Brittle
fracture
* most
common
TABLE
4 Types
Some of the conclusions drawn summarised as follows: Human error is involved at to production. l
l
l
l
Some
The and
% total
categories of
from all
error
these stages
small from
experiences data
collection
Operational errors and faulty maintenance also appear major source for failures arising from human error. This points driver of dependability
to the need for a new breed of a design/materials/production/maintenance as his system lifetime mission.
Failures arising those of sudden
consequences
from failure.
time
dependent
degradation
design
can
be
through
to represent
a
engineer as the cycle with
processes
outweigh
of failures
consequences of failures One financial terms.
are obviously of the main
numerous aims of
and this
often tragic in human paper though is to
205
Failure types
contribute to any ideas and other motivations towards failure prevention. It seems likely therefore that numerate approaches to financial implications rather than human ones could be more successful as possible persuaders for action. Cynical as this may be, it appears to be more appealing to the modern rhetoric of politicians and other major decision makers. At the same time, if successful, the altruism of sociologists and other caring people left out of the decisions arena would also be satisfied. There are two major “after-the-event” features of failures which can be analysed numerately. The first is an indirect one - litigation involved in loss or other liability claims. The second is direct - loss of productive plant. i)
Costs of litigation and their effects. Some statistics on tort costs and trends are available for the USA 131. Amongst these are . tort costs linked with product failures are high worldwide. In the USA an aggregate estimate for 1987 is about 2.5% of Gross National Product. This is between 3 times that of Switzerland and 6 times that of Japan. l
before growth. growing
World War II GNP was growing After World War II this trend at a compound rate of 12%.
at faster has reversed.
rates Tort
than costs
tort are
.
over a period of 12 years up to 1986 the rate liability cases is three times higher than cases in the private and Federal sectors.
.
since 1977 the accident rate in general aviation has continuously reduced. In spite of this, the cost of accident claims has risen seven-fold during the same period. As a result, a whole industry has been wiped out in the USA. These are all highly negative features in terms of the Failures Vector of Fig. 1. Although these features are for the USA, it is not difficult to speculate that the rest of the world will follow suit if strong, affirmatively driven action is not taken on a vast scale. One positive feature of the American statistics is an overall steady decline in workers injury and death rates: . in a forty year period since 1946 the death rate of workers from accidents has declined from 33 per million to 5 per million. The figures are 40 per 1,000 to 12 per thousand for in juries. during the same period the number of workers has increased from 40 to 120 millions.
of growth non-product
of
product liability
l
An inference which could be drawn from these sparse statistics is that whilst the law profession has created a huge business called litigation, the engineering profession remains impotent in spite of the fact that accident fatalities and injuries have dramatically reduced. Failures will still continue and whilst the vector may change even further towards “after-events” its could magnitude grow inexorably as operating conditions and other demands become harsher. ii)
Economic effects of failures An approach taken by Faria [41 towards failures is to restrict investigations fracture, corrosion and wear. This is the analysis in earlier parts of this
analysing the economic effects of to failures mainly caused by in accord also with the results of paper. Faria’s investigations were
206
R. K. Penny
focussed on the USA and Europe, categorised according to various parameters. Amongst these were industrial sectors, direct costs of fracture and the ways and means and costs of effective fracture prevention. Some of the most significant features are For the USA a) . across 154 industrial sectors involved in the production of articles ranging from aircraft to process plant using mainly metallic materials, the cost of failures by fracture was 4% of the USA GNP. On 1982 values of the USA dollar, this is approximately $120 billion, judged to be accurate to 210% 151. .
b)
a similar concluded
investigation of the economic effects of that the USA lost about 4% of its GNP [61.
corrosion
For Europe The objectives of European studies were much the same as those of the USA ; to provide economic evaluations of the effects of fracture and of erosion and wear for each type of equipment used within different sectors of industry. Similar conclusions were reached: losses due to fracture to 12 European countries belonging to the EC amounted to about 4% of the global GNP, judged to be accurate to f 25% [71. l
l
.
the losses due to the effects of British and German investigations those countries. earlier losses, studies,
erosion amount
reports with similar objectives lead to similar conclusions to i.e. about 4% of GNP.
and wear according to 2% of the GNP
insofar those of
as the
to of
corrosion American
These estimates show that the costs of advanced nations on account of failures caused by fracture, erosion, corrosion and wear can amount to about 10% of GNP (roughly 5 x 10” ECU). According to Faria 141, if indirect and consequential costs are accounted for the influence of fracture alone, on the total cost of products, can be as high as 25% (for heavy equipment with high costs) and 2% (for medium size, consequential light equipment with low consequential costs). He also refers to some cases where the total cost incurred by fracture failures attained 100% and more of the product costs ; the products were not specified. Causal
factors
of
failures
Taking into account the American and European studies described together with information from insurance companies, attributable to failures by fracture were categorised as follows .
. . . .
design faulty material manufacture and assembly use/misuse unknown
15% 5%
(22%) (14%)
25% 45% 10%
(31%) (33%)
briefly some
factors
The bracketed figures are taken from Table 3 above for comparative purposes. Considering that the sample size, types of product and date (1969) over which the comparative figures were obtained, the same trends appear in the larger
Failure types
sample which contains a wider range of industries and more recent information (19911. There seems to be little doubt that factors involving major human inputs : design, operation and maintenance, figure too highly at an estimated 60% (55%) in the failure samples. To this has to be added further human fault possibilities during manufacture and assembly. If this is the case for advanced nations, what is the state of developing countries where technology transfer is bound to give room for even greater human error? This is not necessarily because the skills gap is so large (even though it usually is) but for a multitude of other reasons, not least of which is communication. A simple example at the consumer level is with product instructions. A product has passed all its tests in, say, an Eastern European country, is packaged beautifully and sent off, say, to Malawi. The purchaser hires his plumber or electrician, say, to install the item. The tradesman cannot read the installation instructions, gets on with the job as best he can, tests the system and it appears to work. The owner uses the item for the first time and it explodes ; the tradesman did not set the over-pressure cut-out device Of course, such an event should have been according to instructions. anticipated by the designer anyway, but it wasn’t. It seems clear that there is an urgent need for an emphasis on education and training schemes aimed primarily at producing more people who are capable and the of holistic approaches to engineering design manufacturing technologies. The notion of an educated person being a scholarly individual who has been neither educated nor trained in the exercise of useful skills is no longer acceptable. The present imbalance between acquisition of knowledge with use of it in ways which are relevant and in ways which are relevant outside the education system has to be weighed in the reverse order of the present day and those of the cloisters. As was remarked earlier, the challenges of design are far greater than those of research without goal commitment. In this respect, many of the advanced (technological1 countries are not keeping up with the needs of “society”. The Failures Vector is mainly dependent on one resource - the human one. SOME
REMEDIAL
ACTIONS
The human resource is an enormous one which is virtually untapped and a badly educated and trained one. These are strong words but the Failures Vector tells the story. How can it be that the Crystal Palace, which covered 19 acres of space in London and was built in 17 weeks for the 1850 World’s Fair, operated without accident for many decades until it was burned down, whereas walkways in the Hyatt Regency Hotel collapsed within weeks of opening a few years ago in Kansas City, with disastrous consequences? In the latter case, simple design features which led to the failure were not checked by calculation or test. On the insistence of Queen Victoria, walkways and galleries of the Crystal Palace were tested in spite of there also being calculations to check its innovative design principles. The Hyatt hotel building was not an advanced or construction method but the designers did not one in its architecture anticipate possibilities for collapse. The Palace Crystal pre-dated skyscrapers and was unique at the time for its type and lightness of construction with ingenious structural forms to combat wind resistance. The designers successfully anticipated possible failure characters and tested for them. Easy in retrospect to make comparisons, but that such catastrophes as we witness today which, with a little help, undergraduates should be able to assess is worrying. All the more so that a couple of mechanics - the Wright discovered relevant brothers - successfully laws of aerodynamics, designed their structures, tested them and then flew them. Exceptional people undoubtedly, but it is unlikely today that mechanics would get so far even if
R. K. Penny
208
they did have the ambition. Are such people around today? some statistics based upon IQ testing, for what it is worth, are available for various groups of people as follows 191: Specialty
IQ Range
Ph. D Engineer Draughtsman Production Manager Clerk Lathe Operator Weaver Labourer
loo-169 100-151 74-155 82-153 68-155 64-147 26-145 26-145
Mean
IQ
130 127 122 118 118 108 97 96
These data show that there are few dull Ph.Ds but there are many bright and very bright weavers, . clerks and labourers. (In fact, three times as many labourers as Ph.Ds have IQs over 130, because there are so many more labourersl. In general, the mean difference between any two. groups on any dimension is not as great as we sometimes like to believe and the spread and overlap are very great. Of course, it takes many other characteristics than the IQ to find more like the Wright brothers. The resource is available though. How can we best benefit from its potential? Some suggestions follow. Practice
directed
learning
Much has been said and written over the last few decades about improving human reliability in engineering as a means for reducing product unreliability and failure. Most of these discussions have centred around ways and means for rectifying what is - for example, improving the knowledge of production engineers and their respect for quality or for better ergonomic design. There has been much debate about the “image” of an engineer held by the general public. Even more debate has swung various education pendula from science to applied science to engineering science in order to gain a more visible “image” but that has not worked in anybody’s favour. Injections of engineering design into undergraduate courses are often given, under protest, by academics who have never practiced engineering. A major result, of little benefit to anybody, is the creation of design “science” an apparently new subject which would otherwise be called system engineering. Finally, calls for management science have sometimes won over curricula planners to add a part course on the subject to engineering course ; and then a bit of economics and so on. It is surprising that engineers have rarely approached the job of engineering curriculum planning in ways that they design hardware and software. There are notable exceptions to this generalisation, of course, and the efforts of A Rosenstein and M Tribus and of J Dixon, for example, in the USA and of W Betz and M Pahl in Germany are all well known. A recent major analysis 181 has built on the efforts of Rosenstein, Tribus and Dixon with a view to helping in the development of young engineers who can exercise their creative skills in cooperation with others ; who have the capability to initiate, undertake and complete tasks on time and within set budgets ; who have the ability to work within and contribute successfully to everyday life. Readers of this paper may well ask “what has this got to do with failure prevention?” The answer is, not much, in the near future, but the essence is that the attitudes needed in the drive towards good engineering - which includes failure prevention - would be more successfully inculcated than in present schemes of education and training. Present attitudes of young graduates are too often geared towards nicely packaged, pre-digested/stated
209
Failure types
- the easy part problems as a lead in to analysis particulate way rather holistically. The analysis performed in 181 is based upon the graduates should be required to fulfil in satisfying that employers have of them. .
l
.
.
engineering
-
in
a
following premises that the valid expectations
remedying weaknesses in primary and secondary requires a better motivation towards engineering, basic subjects and basic skills and improving working
school the habits
education. underpinning
This of
giving students an image of engineers in industry. Industrial companies are the caretakers of technology as users and developers. Engineers in those companies must be seen as professionals, capable of playing an effective part with others in wealth-creating activities. ” . . . . not just interested in making cars but making money-making cars . . . . ” recognising that a major engineer is communication providing attitudes workplace
l
of
ensuring reliability, technical
time
consumer
in
the
life
of
a professional
a balanced curriculum which encourages and develops towards the engineering profession and to industry
development thoroughness astuteness
Laws
of
the and
personal attributes social concern as
store of Scientific
of Learning
of well
as
Knowledge
positive as a
pragmatism, those of
J
Speedof Scientific
Advances
Future wxds of an Exploding l’opulation
Academic
Increasing complexity New Systems
Traditions
Figure
6. Curriculum
of
Constraints
The analysis was then performed by examining the most obvious constraints which focus on curriculum design (Fig. 61. Course architecture (Fig. 71 was then relatively easy and from this, detailed design also followed. The course architecture is unusual in some important respects:
R. K. Penny
210 .
.
l
l
l
inputs to it are carefully screened and selected (just as a designer screens and selects materials for any job in hand). The screening uses available tools for personal aptitude testing a two year (40 week year) Foundation continuum provides for and assesses student potential for technician and engineering work. This continuum is a common one and contains no specialist options further selection by two stages is designed with a view to some specialism preferences which are served through a project basis. This is the Initial Formation stage where two pathways for graduation are provided and in which the designer/materials/production interactions are portrayed graduation at any stage is accompanied by programmes of continuing education and training the basis throughout is one of practice directed education in which the laboratories are factories and other everyday workplaces
A 3 E 1 E c T
C A T
T
CHOSEN TOPIC
MENTOR SYSTEM
0 N
0
COUNSELLING
Figure Other
FO”p
PROJECT ENGINEERING
s
P P L
0 N
Fa YEAR
remedial
COUNSELLING
7. Course
Architecture
actions
Cultivation of the attitudes of the human resource is a major task which has to be undertaken as a matter of urgency. However, the products of schemes such as practice directed education will take time to be of any measurable effect on the Failures Vector. Much cooperation on an international basis is vital and the costs are negligible compared with those of continued failures as has been demonstrated by Faria 141 The main stumbling block will be a human one the educators. The reason for this is that the educators, being human, believe that what was right for them as students must be right for their students. The research syndrome which has grown into the engineering streams of a modern university and out of a respect for science and discovery will also be hard to overcome in spite of the high cost and low productivity of university research. Private initiative to overcome these obstacles will have to be led by industry whilst governments seem hell-bent on perpetuating present systems of education and training. Whether or not the new breed of human engineering resource is generated,
211
Failure types
there are secondary, but vitally important help reduce the Failures Vector magnitude. .
inputs, being Some of them
made are
in other
ways
to
codes of practice and design rules. Good contemporary examples here are the well-known ASME guidelines for pressure vessel design and the lesser known Nuclear Power p. l.c. (UK) guidelines 1101 for high temperature designs containing defects guidelines on risk issues which set out different risk factors and their These are interactions, as well as suggested implementation actions. essentially awareness guidelines as aids to professional responsibility and an example from the UK has been published recently Ill] goal-directed research and results dissemination with particular reference to fracture problem solving. A good example is the creation of ESIS (European Structural Integrity Society) through the initiatives of the European Joint Research Centre of Petten, Holland 141.
l
l
CONCLUDING REMARKS Growth in what has been termed the Failures Vector is costing enormous losses in financial, economic, human and any other terms. The causes for this are largely of human origin. Whilst guidelines by way of codes of practice and other means are being devised and disseminated by authoritative bodies on an international basis, it is essential that new schemes for preparing young people for careers in engineering are designed and implemented as quickly as possible. These are most likely to succeed if they are propelled by private initiatives backed by industry and if they are practice orientated.
ACKNOWLEDGEMENT Figures
2 and 3 by courtesy
of D L Marriott.
REFERENCES 1. 2. 3. 4.
5. 6. 7. 8. 9. 10. 11.
“Modern Materials in Manufacturing Industry” Report by the UK Fellowship of Engineering at the request of the Dept. of Industry 0 1983 R K Penny. “Some Aspects of Design”, Liverpool Engineering Society Journal, vol. XCV, 5, July 1969. B Ross. Failure Analysis Associates, California, USA. Personal communication. L Faria. “Economic Effects of Failures of Systems”, International Conference on Structural Failure and Product Liability, Vienna, November 1993, Proceedings to appear. “Economic Effects of Fracture in the United States”, US Dept. of Commerce, Nat. Bur. Stand. Special Publ. 647-l & 2, March 1983. E D Verink, “Corrosion Economic Calculations”, Metals Handbook, vol. 13 Corrosion, ASM International, Ohio, 1987. “Economic Effects of Fracture in Europe - Final Report”. Commission of the European Communities, 1991. “An Opportunity for a New Initiative”. 0 Engineering Formation cc., Cape Town, 1993. A D Swain. “Improving Human Performance”, In Corn. Tee. Training Services, Camberley UK, 1974. R5 and R6 Procedures, 0 Nuclear Power p.l.c., 1991. “Engineers and Risk Issues”. Q The Engineering Council, ISBN 0-95166117-5, 1993.