Critical Path Analysis in Practice

Collected papers on project control

Gail Thornley, Gail Thornley

• Publisher: Routledge
• Year: 2013
• ISBN:
  9781136438240
• Edition: 1
• Topic: Medicine
• Subtopic: Health Care Delivery

Tavistock Press was established as a co-operative venture between the Tavistock Institute and Routledge & Kegan Paul (RKP) in the 1950s to produce a series of major contributions across the social sciences.
This volume is part of a 2001 reissue of a selection of those important works which have since gone out of print, or are difficult to locate. Published by Routledge, 112 volumes in total are being brought together under the name The International Behavioural and Social Sciences Library: Classics from the Tavistock Press.
Reproduced here in facsimile, this volume was originally published in 1968 and is available individually. The collection is also available in a number of themed mini-sets of between 5 and 13 volumes, or as a complete collection.

Part I
Review of Basic CPA Methods

The first chapters of this Part outline the problem areas and industries in which CPA has been successfully applied in the UK, and briefly introduce the essential elements of the technique. Newcomers to the subject are advised to refer to a more complete description of the technique; for example in one of the books recommended in the selective reading list.

The arrow-diagram method, described in Chapter 2, is the most commonly used, but is not the only method of drawing network diagrams. Other methods include the circle and link technique which was described at the CPA Study Group meeting of 15 September 1966 by Dr C. J. Anson of Urwick Orr & Partners Ltd, and the method of potentials, which is described in Chapter 3. The different methods have their own advantages and disadvantages, but all are essentially methods of representing the logical relationships between jobs that have to be performed and calculating the consequential time limitations.

1 · The Scope of the Method

D. WILLIAMS

History

A number of different approaches to the problems of planning and scheduling contributed to the development of the subject of these papers. Imperial Chemical Industries and the Central Electricity Authority (now the Central Electricity Generating Board) were using the basic concepts in Britain by 1955 and 1957 respectively. In 1958, two of the most widely known systems of analysis, PERT and CPM, were announced in America. PERT, standing for Program Evaluation and Review Technique, evolved from the need to develop an improved method of planning and introducing the Polaris project. In the military environment the main consideration was time reduction, but a parallel development in the civil field by the Du Pont Chemical Company sought to achieve a balance between cost and time. This research yielded CPM, the Critical Path Method, which produces either the cheapest way of executing the project or alternatively the cheapest way of doing the job as quickly as possible. Not only have PERT and CPM lost their original connotations, but a multitude of other expressions have been developed.

Some areas of application

The object of this section is not to give a comprehensive survey, but merely to indicate to the reader the scope and range of potential application. It is inevitable that a survey as brief as this will omit to mention many firms with wide experience of the techniques, and indeed will fail to indicate the width of experience within any one firm.

A number of civil engineering firms have started to use the techniques only because the firms which invited their tenders insisted on the production of an appropriate network. This state of affairs arose from the pioneering work done in England by leading firms like Richard Costain and John Laing Construction. New manufacturing and chemical process plants have been designed and commissioned using CPA by firms such as British Oxygen Company and Distillers Chemicals and Plastics Ltd. Housing developments by Croudace, and other leading builders, have been controlled through Network Analysis. During 1966 a firm reconstructing a shop in Cologne exhibited its network diagram on the protective hoarding and brought it up to date so that passing members of the public could see the progress being made.

Applications in the other engineering fields include locomotive maintenance by the British Railways Board and plant maintenance at the Steel Company of Wales. Apart from using networks on construction projects, the National Coal Board controls pit operations by the routine use of a planning network at each colliery. Eight-year programmes for all new generating stations are being networked currently by the Central Electricity Generating Board. The United Kingdom Atomic Energy Authority uses Network Analysis for major construction projects and plans reactor overhauls using resource scheduling. British Petroleum uses the technique for refinery maintenance.

The British Coal Utilization Research Association has examined the ways in which the network concept can be utilized in conjunction with the uncertainties inherent in the research and development fields. Alfred Herbert, a leading machine-tool manufacturer in the UK, uses Network Analysis in the design and production of new lines. Unilever uses the technique to plan the development and launching of new products, including packaging, advertising, and consumer research activities.

An interesting application occurs when a network is drawn for the installation of a computer; the analysis of the network is frequently undertaken using another computer. In a similar manner, networks have been drawn to improve a number of clerical procedures, notably in the accountancy field. The British Aircraft Corporation is among the firms using small standard networks which are integrated into a large network for specific projects.

The firms mentioned above are known nationally. However, there are a great number of quite small firms which have utilized the techniques in many of the ways described. The size of the networks and the complexity of their analysis are more dependent on the nature of the project than on the size of firm or even the financial value of the work. Sometimes it might cost more to analyse the project than might be considered appropriate. However, when a task is repetitive, the initial expenditure of effort can repay handsome dividends. One repetitive task which has benefited from Network Analysis is a certain surgical operation for which the time has been reduced significantly.

Some benefits arising from the techniques

What kind of benefits can one expect from the application of Network Analysis? A firm just starting to use it will probably derive a lot of benefit from the need to think about all aspects of the project in advance of its commencement. The manager who does not plan at present, or whose plans frequently seem to go askew, will find no haven in Network Analysis unless he is prepared to be thorough. However, with comparatively little effort he will find this is at least a way in which complex operations can be planned efficiently. His efforts, together with those of his colleagues, will produce an integrated approach to projects, and the responsibility for each part of the work will become clearly established. Information will be provided in a form which allows each manager to control his own tasks by exception rather than in total.

It is frequently thought that Network Analysis is confined to the planning of the construction phase of a project; the preceding section has indicated that it may be used for a variety of purposes including the planning of the planning itself. Many projects may be planned and executed in a variety of ways. What is the 'best' way? There may be a number of conflicting criteria against which each method must be measured. Networks enable these alternative methods to be described and evaluated both quickly and accurately, and then management may select the most appropriate approach to the job.

Network Analysis may also be used as a method of project control by updating the network as the project proceeds and thus anticipating hold-ups in time to take preventive action. Part III describes extensions of the basic technique which provide means of resource and cost control.

A number of other benefits of using these techniques will emerge from the following chapters. We do not claim that Network Analysis is a panacea, but during the past few years many firms have found it provides a most powerful addition to their armoury of management science subjects.

2 · Introduction to the Basic Method

D. WILLIAMS

The steps in network analysis

It is helpful to think of Network Analysis as a number of steps.

• (i) Understand the logic of the strategy
• (ii) Construct the network
• (iii) Obtain activity duration estimates
• (iv) Identify the critical...