Human error hazards

Initial Costs Demolition Costs Maintenance Costs Chances of Failure-in Limit States random hazards human error concept deficiency Direct costs of each type of failure Indirect consequences of each type of failure (e.g, H.A.C., boxgirders)... 

A hazard is defined as the potential source of harm (3.5). Hazards include both the characteristics of things and the actions or inactions of people. Identifying hazardous human error potential, as well as the physical aspects of hazards, is an important part of the hazard identification process. All risks with which safety practitioners deal derive from hazards. There are no exceptions. For any particular hazard, the first and best approach is to eliminate the hazard. If there are no potentials for harm, there are no hazards. If there are no hazards, there are no risks. Hazards eliminated result in zero risk from those hazards. But, it is not possible to eliminate all hazards. 

Identification of likely sources of hazards (human error, software etc.) The storm scenario in the worst case could result in very many fatalities. 

Process Hazards Analysis. Analysis of processes for unrecogni2ed or inadequately controUed ha2ards (see Hazard analysis and risk assessment) is required by OSHA (36). The principal methods of analysis, in an approximate ascending order of intensity, are what-if checklist failure modes and effects ha2ard and operabiHty (HAZOP) and fault-tree analysis. Other complementary methods include human error prediction and cost/benefit analysis. The HAZOP method is the most popular as of 1995 because it can be used to identify ha2ards, pinpoint their causes and consequences, and disclose the need for protective systems. Fault-tree analysis is the method to be used if a quantitative evaluation of operational safety is needed to justify the implementation of process improvements. 

As microprocessor-based controls displaced hardwired electronic and pneumatic controls, the impac t on plant safety has definitely been positive. When automated procedures replace manual procedures for routine operations, the probability of human errors leading to hazardous situations is lowered. The enhanced capability for presenting information to the process operators in a timely manner and in the most meaningful form increases the operator s awareness of the current conditions in the process. Process operators are expected to exercise due diligence in the supervision of the process, and timely recognition of an abnormal situation reduces the likelihood that the situation will progress to the hazardous state. Figure 8-88 depicts the layers of safety protection in a typical chemical jdant. 

Inherently Safer Design Rather than add on equipment to control hazards or to protect people from their consequences, it is better to design user-friendly plants which can withstand human error and equipment failure without serious effects on safety, the environment, output, and efficiency. This part is concerned with this matter. 

For many years the usual procedure in plant design was to identify the hazards, by one of the systematic techniques described later or by waiting until an accident occurred, and then add on protec tive equipment to control future accidents or protect people from their consequences. This protective equipment is often complex and expensive and requires regular testing and maintenance. It often interferes with the smooth operation of the plant and is sometimes bypassed. Gradually the industry came to resize that, whenever possible, one should design user-friendly plants which can withstand human error and equipment failure without serious effects on safety (and output and emciency). When we handle flammable, explosive, toxic, or corrosive materials we can tolerate only very low failure rates, of people and equipment—rates which it may be impossible or impracticable to achieve consistently for long periods of time. 

After you record the steps of the job, review each step to determine the hazards that exist or that might occur. There are several ways to identify job hazards evaluate the ways human error might contribute to a hazard, record the types of potential incidents and the physical agents involved, and make sure that procedures are clearly written. 

A critical assembly is a split bed on which fissionable material used to mock up up a separated reactor core that is stacked half on each half. One half is on roller guides so that the two halves may be quickly pulled apart if the neutron multiplication gets too high. Use the Preliminary Hazards Analysis method described in section 3,2.1 to identify the possible accidents that may occur and the qualitative probabilities and consequences. List the initiators in a matrix to systematically investigate the whole process. Don t forget human error. 

A related concept to inherently safer design is user-friendly design designing equipment so that human error or equipment failure does not have serious effects on safety (and also on output or efficiency). While we try to prevent human errors and equipment failures, only very low failure rates are acceptable when we are handling hazardous materials, and, as this book has shown, it is hard to achieve them. We should, therefore, try to design so that the effects of errors are not serious. The follov,/-ing are some of the ways in which we can accomplish this ... 

An opportimity for error recovery would have been to implement a checking stage by a supervisor or independent worker, since this was a critical maintenance operation. However, this had not been done. Another aspect of the unforgiving environment was the vulnerability of the system to a single human error. The fact that the critical water jacket flow was dependent upon a single pump was a poor design that would have been detected if a hazard identification technique such as a hazard and operability study (HAZOP) had been used to assess the design. 

It is therefore useful to distinguish between active and latent errors or failures. An active human error has an immediate effect in that it either directly causes a hazardous state of the system or is the direct initiator of a chain of events which rapidly leads to the imdesirable state. 

Checks of critical process parameters and warnings about hazardous conditions that can cause injury or equipment damage are important factors which determine the occurrence and recovery of human error. The purpose of these checks is to emphasize critical process information. Because of the critical nature of this information, checks and warning should be highlighted in a way that distinguishes them from other notes, and should be located where process workers will not overlook them. 

Inspection of the HRA event tree reveals that the dominant human error is Error A the operator failing to isolate the propane valves first. The other potential human errors are factors only if a propane isolation valve sticks open. Based on these qualitative results alone, a manager rrught decide to periodically train operators on the proper procedure for isolating a failed condenser and to ensure that operators are aware of the potential hazards. The manager might... 

This is a situation where a plant appears to be operating successfully, without a major human error problem. However, management are interested in assessing the systems in the plant from the point of view of minimizing the error potential. This type of exercise is particularly relevant for plants dealing with substances or processes with high hazard potential, for example, in terms of... 

The final element in management s communication of a desire to reduce human error is the identification and elimination of error-likely situations. Every task is an opportunity for a human error, but some situahons represent greater risks than others. Identifying these high-risk situations is not easy and an expertise in applying human factors principles to the workplace is an essential prerequisite for this identification. Eliminating these hazardous situations is often relatively simple once they have been identified. In some cases it may be appropriate to provide error-tolerant systems, which are those that facilitate identification of and recovery from the errors. 

Management must modify the culture and develop human factors awareness in the hazard identification teams so that they will be capable of identifying the potential for human error. A good practice is to involve operators in the hazard identification team. 

Bridges, W. G., Kirkman, J. Q., Lorenzo, D. K. (1994). Include Human Errors in Process Hazard Analyses. Chemical Engineering Progress, May. 

Rasmussen, J. (1990). Human Error and the Problem of Causality in Analysis of Accidents. In D. E. Broadbent, J. Reason, A. Baddeley (Eds.). Human Factors in Hazardous Situations. Oxford, U.K. Clarendon Press. 

There arc oilier methods of hazard identification. A "wliat-if analysis presents certain questions about a particular hazard and then tries to find llie possible consequences of that hazard. The human-error analysis identifies potential human errors that will lead to an accident. They can be used in conjunction with llic two previously described methods.. ... 

Human error is frequently used to describe a cause of losses. Almost all accidents, except those caused by natural hazards, can be attributed to human error. For instance, mechanical failures could all be due to human error as a result of improper maintenance or inspection. The... 

A part of the test plan must include testing for the consequences of equipment malfunction, deviations in process conditions, and human error. Bench-scale equipment, for example, the RC1, is quite suitable for such experiments. By analysis of the process, critical conditions can be defined, which then need to be tested in order to be able to proceed safely from the laboratory to pilot plant studies. In testing abnormal conditions or process deviations, caution is required to assure that no uncontrollable hazard is created in the laboratory. Typical deviations, including impact on the process, are discussed in the following paragraph. 

Lees (Loss Prevention in the Process Industries, 2d ed., Butter-worths, London, 1996), BP (Hazards of Trapped Pressure and Vacuum, 2003), and Kletz (What Went Wrong —Case Histories of Process Plant Disaster, Gulf Publishing Company, 1989) include additional case histories providing valuable lessons about how equipment failures and human errors can combine to inflict vacuum damage. 

Several qualitative approaches can be used to identify hazardous reaction scenarios, including process hazard analysis, checklists, chemical interaction matrices, and an experience-based review. CCPS (1995a p. 176) describes nine hazard evaluation procedures that can be used to identify hazardous reaction scenarios-checklists, Dow fire and explosion indices, preliminary hazard analysis, what-if analysis, failure modes and effects analysis (FMEA), HAZOP study, fault tree analysis, human error analysis, and quantitative risk analysis. 

Fault tree analysis is based on a graphical, logical description of the failure mechanisms of a system. Before construction of a fault tree can begin, a specific definition of the top event is required for example the release of propylene from a refrigeration system. A detailed understanding of the operation of the system, its component parts, and the role of operators and possible human errors is required. Refer to Guidelines for Hazard Evaluation (CCPS, 1992) and Guidelines for Chemical Process Quantitative Risk Assessment (CCPS, 2000). 

Process Hazard Analysis (PHA) can be defined as the application of a systematic method to a process design in order to identify potential hazards and operating problems. It determines the causes and consequences of abnormal process conditions that arise from equipment failure, human error or other events. The goal is to determine whether opportunities exist to reduce the risks of the toll s hazards and then to implement warranted action items. The AJChE CCPS guideline Guidelines for Hazard Evaluation Procedures, Second Edition with Worked Examples is a good resource for fully detailed approaches to process hazard analysis. It provides an introduction to hazard evaluation as well as guidance on ... 

The full range of process maloperations, including system failures that might lead to process runaway will first have to be considered by a systematic evaluation of the plant and process concerned141. These may, for examplel be due to human error, hardware failure, or due to failure of a computerised sequence controller. To assess the likely/ credible maloperations accurately, it is recommended that personnel who will be operating the plant are involved in the hazard assessment. 

Simplify—Design processes and facilities that eliminate unnecessary complexity and that are tolerant of human error. Example Design piping to permit gravity flow of hazardous materials in a plant, eliminating the need for pumps, which can leak. 

This one costly human error had a considerable effect on the Congress, just then in the process of hammering out certain provisions of TSCA—The Toxic Substances Control Act of 1976. In particular those sections dealing with the premarket testing of hazardous chemicals, their labeling and distribution were affected (ref. 154). 

---