Accidents and Human Error

Upon completing this chapter the student should be able to  

Unfortunately, fires, explosions, chemical leaks, and other incidents happen in the process industries. Depending upon the type of plant, its size, work force training, experience, and safety culture, a plant site may experience one or two incidents a year. An incident does not necessarily mean a serious fire or explosion. The most common types of incidents ranked by frequency are  

It is not uncommon in some industries, such as the chemical and electric utility industries, to experience new injuries or fatalities due to the same incidents. Industrial incidents have an eerie way of repeating themselves because organizations do not learn from the past. Individuals learn, but individuals retire or move to different locations and take their knowledge and experience with them. The organization as a whole loses memory. As people retire, move to other plants, or plants downsize, incidents of a similar type tend to recur within the same company at approximately 10-year intervals. 

Investigations of industrial accidents reveal that most are caused by human error. The twentieth century s worst industrial disasters—Bhopal, Three Mile Island, and Chernobyl—helped clarify the complex chain of system problems that lead to human error. System problems are problems caused by a process system with built in design and operating deficiencies. The accidents provided numerous checklists and case studies for control room and equipment design. A partial list of some of the problems found at the industrial sites mentioned above are  

These accidents, and many less devastating incidents that continue to occur today, were linked by an incomplete analysis of human factors. The human side of safety was ignored with high costs. Chemical manufacturers have yet to get over the impact of Bhopal, which killed 3,800 and injured over 200,000. Litigation is still in process. It required 4.5 years and 970 million to clean up after the Three Mile Island nuclear plant accident. That cost is hundreds of millions more than the cost to build the plant. Long-term environmental and health impacts of Chernobyl continue to haunt Russia and her neighbors. 

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THE TRADITIONAL SAFETY ENGINEERING APPROACH TO ACCIDENTS AND HUMAN ERROR... 

Accidents are very rare relative to the number of near accidents and human errors. Fortunate as it may seem, this poses a real problem for complex systems with a high catastrophy potential (nuclear power plants, chemical plants, commercial aviation) few accidents means few cases to analyse and hardly any feedback to learn from. This leads to the undesirable situation of ad-hoc corrective measures after each single accident, because the database is far too small to generate statistically sensible preventi ve measures. 

ETA breaks down an accident iato its contributing equipment failures and human errors (70). The method therefore is a reverse-thinking technique, ie, the analyst begias with an accident or undesirable event that is to be avoided and identifies the immediate cause of that event. Each of the immediate causes is examined ia turn until the analyst has identified the basic causes of each event. The fault tree is a diagram that displays the logical iaterrelationships between these basic causes and the accident. 

The result of the ETA is a Hst of combiaations of equipment and human failures that ate sufficient to result ia the accident (71). These combiaations of failures are known as minimal cut sets. Each minimal cut set is the smallest set of equipment and human failures that are sufficient to cause the accident if all the failures ia that minimal set exist simultaneously. Thus a minimal cut set is logically equivalent to the undesired accident stated ia terms of equipment failures and human errors. 

Frequency Phase 1 Perform Qualitative Study, Typically Using HAZOP, FMEA, or What-if Analysis. To perform a qualitative study you should first (1) define the consequences of interest, (2) identify the initiating events and accident scenarios that could lead to the consequences of interest, and (3) identify the equipment failure modes and human errors that could contribute to the accident... 

In April 1982, a data workshop was held to evaluate, discuss, and critique data in order to establish a consensus generic data set for the USNRC-RES National Reliability Evaluation Program (NREP). The data set contains component failure rates and probability estimates for loss of coolant accidents, transients, loss of offsite power events, and human errors that could be applied consistently across the nuclear power industry as screening values for initial identification of dominant accident sequences in PRAs. This data set was used in the development of guidance documents for the performance of PRAs. 

Viewed in this context, the Three-Mile Island (TMI) accident was the coup de grace for an already foundering industry. In spite of the fact that the hydrogen gas bubble that accumulated in Reactor 2 did not explode, although some contaminated gas escaped and that the commissions who investigated the accident faulted human error rather than equipment failure, TMI caused (as the New York Times... 

Leplat J., 1987. Accidents and Incidents Production Methods of Analysis, in Rasmussen et al. (Eds.), New Technology and Human Error, Chichester. 

Human errors may be accidentally performed by all personnel - designers, engineers, operators, and managers. Some theories attribute up to 90% of all accidents to human errors. 

The worst nuclear power accident in the U.S. occurred at the Three Mile Island plant in Pennsylvania. In this accident no one was killed and no one was directly injured. The event at Three Mile Island occurred from faulty instrumentation that gave erroneous readings for the reactor vessel environment. A series of equipment failures and human errors along with inadequate instrumentation allowed the reactor core to be compromised and go into a partial melt. The radioactive water that was released from the core was confined within the containment building and very little radiation was released. In the Three Mile Island incident, the safety devices worked as planned and prevented any serious injury. This accident resulted in improved procedures, instrumentation, and safety systems being implemented. 

It is easy to blame accidents on human error, but good design can often minimize this.161 Avoid poor lighting or contrast. Provide a checklist so that the operator will find it easy to recall all of the necessary information. Most valves have right-handed threads. Do not mix in any that have left-handed threads. Mount them so that they are easy to access, and the labels are easy to see. 

There are many factors that can contribute to an accident [4] human error [5,6], equipment malfunction, upset conditions, fire or explosion near the apparatus [7], improper procedures, and severe weather conditions. There are also many potential dangers caused particularly by fires and explosions such as flying shrapnel, pressure waves from a blast, high heat loads from flame radiation [8-10], and high temperatures. All of these can have severe consequences to both people and equipment and may need to be considered in minimizing the potential impact of an incident. 

The Bhopal accident was the result of a combination of legal, technological, organizational, and human errors. The immediate cause of the chemical reaction was the... 

The release of methyl isocyanate (MIC) from the Union Carbide chemical plant in Bhopal, India, in December 1984 has been called the worst industrial accident in history Conservative estimates point to 2,000 fatalities, 10,000 permanent disabilities (including blindness), and 200,000 injuries [38]. The Indian government blamed the accident on human error—the improper cleaning of a pipe at the plant. A relatively new worker was assigned to wash out some pipes and filters, which were clogged. MIC produces large amounts of heat when in contact with water, and the worker properly closed the valves to isolate the MIC tanks from the pipes and filters being washed. Nobody, however, inserted a required safety disk (called a slip blind) to back up the valves in case they leaked [12]. 

Kjellen, Urban. 1987. Deviations and the feedback control of accidents. In New Technology and Human Error, ed. Jens Rasmussen, Keith Duncan, and Jacques Leplat, 143-156. New York John Wiley... 

Operation and System Safety Group. It will cover topics such as criticality control, administrative controls to prevent accidents, radiation protection, normal emission, system failure mode, and human error. 

An accident at a nuclear power plant can be caused by many combinations of anomalous initiating event, malfunction and human error. The types of possible accidental situations are studied in the specific safety analysis of each plant and the safety systems described above are designed to prevent, or mitigate the effects of all the accidents chosen as DBAs. Table 3-1 provides an approximate indication of the effectiveness of various safety systems in limiting external releases in a typical loss of coolant accident (the break of a large primary circuit pipe). The figures are for the release of iodine-131 (often assumed as the reference isotope in indicative evaluations of source terms and for a 1000 MWe reactor). As can be seen, the reduction of the releases caused by the safety systems is very significant and corresponds to a factor of the order of one million. 

Direct radiation exposure -Irradiated isotope production target, up to 20,000 curies -Fresh waste barrel, up to 120.000 curies -Entire waste inventory, up to 500.000 curies -Forklift accident -Mishandling during waste storage -Combined mechanical failure and human error Direct exposure to these radiation hazards is normally prevented by radiation shielding. 

One of the major contributory factors in road accidents is human error (for example violation of speed limits). The type, size and frequency of these human errors depend on the whole road system and traffic regulations, which must be designed in a way to be safe and protective of such human errors. 

By doing this, I rely on earlier studies that indicate accidents caused by a combination of five main dimensions (human-vehicle-environment-road-system). One of the major contributory factors in road accidents is human error. The size of this human error depends on the whole road system and traffic regulations. Rumar (1999) has shown that the major contributory factor in road accidents is the human factor. The results are taken from two in-depth studies and analyses carried out in the UK and USA. Both studies indicate that the hmnan factor (road users), overlapping with other factors, is the major contributory factor in 94/95 % of accidents as shown in Figure 5.6. 

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