Tripod Delta: Proactive Approach to Enhanced Safety
- P.T.W. Hudson (Leiden U.) | J.T. Reason (Manchester U.) | P.D. Bentley (Shell Intl. Petroleum Mij. B.V.) | M. Primrose (Shell Intl. Petroleum Mij. B.V.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- January 1994
- Document Type
- Journal Paper
- 58 - 62
- 1994. Society of Petroleum Engineers
- 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 6.1.5 Human Resources, Competence and Training, 1.6 Drilling Operations, 4.1.5 Processing Equipment, 4.6.2 Liquified Natural Gas (LNG), 4.2.3 Materials and Corrosion, 4.6 Natural Gas, 6.1 HSSE & Social Responsibility Management, 4.1.4 Gas Processing, 4.1.2 Separation and Treating, 4.3.4 Scale
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Tripod Delta (diagnostic evaluation tool for accident prevention) is achecklist-based approach to carrying out safety "health checks." Thispaper describes the theoretical background of the approach, which is based on amodel for understanding the role of human error in accidents. The method forconstructing databases from which to make checklists and use of the system togenerate remedial safety plans are described. Finally, the implementation isdiscussed and the status is reviewed.
Tripod is an approach to safety developed by the U. of Leiden and the U. ofManchester in close cooperation with the Shell Intl. Petroleum Mij. B.V.E&P function. Tripod attacks underlying safety problems with specialreference to human error, which is seen in failures at both individual andorganization levels. A central concept in Tripod is the "latentfailure," the potential cause of future accidents. Tripod Delta is adiagnostic tool developed to help identify such underlying problems beforelatent failures generate active failures (the immediate causes of accidents).This paper describes the background of Tripod Delta, how it operates, and thecurrent status of the system.
Accidents, Unsafe Acts, and Underlying Causes. Accidents have a number ofimmediate causes, many of which have a human origin. For an accident to takeplace, unsafe human acts must interact with triggering events, such as abreaking cable or a well kick. When the combination circumvents availabledefenses, the result may be an accident or a near miss. All too often,investigation of an incident focuses on the immediate events and humanfailures. This concentration on the direct causes (active failures) also oftenapplies to proposals for prevention of future incidents. However, the eventsleading to accidents do not arise spontaneously. The shortcomings that can beidentified after an accident are often present long before as latentfailures.
The general Tripod model (Fig. 1) in cludes three basic components of theaccident process.
1. Accidents happen when defenses are breached.
2. The unfortunate sequence of events involves the combination of one ormore unsafe acts in the context of specific triggering conditions (which maythemselves be technical or human in origin).
3. Behind the unsafe acts and conditions is a history of causes, classifiedinto a limited set of general failure types (GFT's) shown in Table 1.
This restricted set of 11 GFT's has been identified in field studies andfrom analyses of major accidents. The list was defined by providing a generalset of terms adequate to describe latent failures and by distinct ways toremedy the problems identified. The communication GFT, for instance, coversboth technical failures (e.g., a poor or nonexistent telephone system ordifficult radio communication) and human failures (inability to pass on or tounderstand messages). The important factor in a potential accident is that thevital information may not be available to the proper people at the right time.Similarly, the hardware GFT refers to the quality and availability ofcomponents, tools, and equipment. Problems in any of these areas may leadpeople to create situations that can lead to hardware failures later, such asaccepting corrosion, installing in correct material, or using the wrongtools.
The view taken in Tripod is that it is more effective to concentrate on theconditions defined by the GFT's rather than to attempt to stop the unsafe actsas they occur. The GFT's behind the large numbers of unsafe acts and triggeringevents form a natural and more limited set of targets for improvement.
Safety Management and Proactive Approaches. An important starting point insafety management involves identifying the necessary components of goodmanagement practice. Shell's Enhanced Safety Management Principles embody suchan approach, stressing such factors as the necessity for a firm commitment tosafety, line responsibility for safety, and regular audits. Once managementsystems meet such principles, it generally becomes necessary to determine whereattention must be directed.
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