Task Analysis of Methods for the Operation of Cranes

POSTER

Goals Operatos Methods and Selection rules (GOMS)

• Cognitive approach.
• Improves the interaction between humans and machines.
• Start after a basic Task analysis method.
• It gives both qualitative and quantitative measures.
• It produces valid predictions.
• Helps to discover usability problems.

EXECUTIVE SUMMARY

 Operating a crane is a complicated job that demands not only extensive skills and experience but also a comprehensive understanding of the crane conditions and its surrounding environment throughout the operation of the crane. When performing a lifting operation, an operator must comply and process information such as environmental changes, crew communication, and crane feedback. Task analysis helps to remove precondition that causes errors and a tool to design a new system. In this report, we considered three types of task analysis methods: Hierarchical Task Analysis, Operator Action Event Tree and GOMS method for the task analysis of the operation of cranes. Out of these three, a combination of Hierarchical task analysis and GOMS method can be combined as a single framework for conducting task analysis. Hierarchical task analysis does not handle higher cognitive components of tasks, but GOMS does. So, we can use HTA as a primary task analysis method, and the result from HTA can be used to start GOMS analysis.

INTRODUCTION

 The building construction projects are highly mechanised nowadays. With the growing mechanisation in construction, most of the structures are prefabricated and assembled on site. It has resulted in less dependence on construction equipment on-site and more dependence on lifting and transporting equipment. Lifting equipment and material handling equipment now rules the building construction sites and constitutes the crucial element in achieving productivity (Shapira et al.,2007).

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 Cranes are used for most of the lifting operations in construction. Crane-related accidents are less common compared with other types of accidents; however, once they happen, it will result in a significant impact on cost, delays and most importantly, severe injuries and fatalities. A competent crane operator requires skills, experience moreover a complete knowledge of the crane surroundings and operations. While lifting, a crane operator continuously monitors environmental changes such as wind speed and the presence of foreign objects and adjusts the crane manoeuvre speed or changes the lift strategy in response to those modifications. At the same moment, the operator must understand the crane capacity and status using the load chart, boom angle indicator, or load moment indicator. Moreover, lifting operations usually involve coordination with the riggers or signal people. However, the information the operator gets from these sources is not always accurate or complete for various reasons, such as an obstructed line of sight or poor communication or misunderstanding. (Fang & Cho, 2017).

 From a cognitive perspective, crane operators’ cognitive load may be viewed as the cognitive capacities of the operator that are needed for task performance to meet performance expectations (Gopher and Donchin 1986). We can’t completely rely on an operator to recognize and mitigate hazards when considering the factors such as fatigue. Because of many construction activities depend on crane lifting for everyday activities such as delivering the materials and erection of structures, crane operators usually start their work very earlier and finish much later than most other construction crews. Therefore, crane operators are often more fatigued than their colleagues on other crews and may have a more decreased cognitive capacity than others when approaching the end of the day. In addition to fatigue, distractions from other sources also reduce the available mental capacity allocated to controlling the crane (Liang et al. 2007) and thus result in a significant threat to the safe operation of cranes (Visser et al. 2012). 

 Task analysis is a vital tool for safety management system because it helps the users to understand the goal, step by step procedure in using the system, the situational awareness and critical elements that help the designer to assure that they achieved the goal. For assessing and reducing human errors task analysis is a necessary process. Some of the advantages of task analysis are it can be applied to eliminate the errors before it could happen and also it can be used as a tool for designing a new system or for modifying an established system. Failing to conduct task analysis before designing may end in the creation of systems that are deficient in satisfying the demands of the tasks the user wants to perform (Drury, 1983). Task Analysis is the method of breaking a piece of work into small elements and examining the relationship between those elements (Gillan, 2012). This report will focus on three analysis methods, which is appropriate for crane operation.

DISCUSSION

 Task analysis is performed in three phases. They are data collection, task description and task analysis. Data collection involves the collection of data about the task and work systems, which is mainly done by observing the task. As a part of the task description, a task dictionary is developed, which is essential for defining the task. Making clear definitions and terminologies help in understanding the clarity of task and also helps in recreating it in the future. Task description helps in identify start to finish the process by identifying step by step activities involved. It usually explained by flow chart or descriptional form. Once the task description has been made, the next step is comparing the demands of the task and the abilities of the system (Drury, 1983). On a proper analysis, the mismatch between the task demands and system abilities can be identified and use them to generate an improved solution system.

Hierarchical Task Analysis (HTA): This is an economical and systematic method of describing how work is organised in order to meet the overall objective of the job. HTA breaks a goal into a series of sub-goals and task components. Additional information is given for each step, including possible errors, the probability that the error will occur at this step, the severity of the error, or possible design solutions to decrease the probability of the error occurring (Gillan, 2012). Hierarchical Task Analysis can be represented in two ways: diagrammatic and tabular. The most easily assimilated method is diagrammatic, but tabular format gives very detailed information about the system.

 Some of the advantages of Hierarchical task analysis are it helps in focusing on the crucial phase of the task which can have a significant impact on crane operation. HTA can be used as an error analysis tool for performance of expected operations. The tool is most effective when used in combination between task analyst and the people involved. Hierarchical task analysis can easily be implemented in product/system analysis, once the initial concept has been understood.

 Some of the disadvantages of hierarchical task analysis are the analyst requires to develop a measure of skill in order to analyse the task efficiently since the technique is not an easy procedure that can be applied instantly. However, the required skills can be acquired reasonably quickly by practice. Hierarchical task analysis provides more descriptive information than analytical information. Hierarchical task analysis does not handle higher cognitive components of tasks such as decision making.

Operator Action Event Trees (OAET): The operator action event tree method is based on the assumption that human behaviour in response to an event occurring in the environment can be considered in three stages of activity. Firstly, observing the event, then thinking about it and responding to the event (Hall et al. 1982). The tree-like diagrams help in describing the actions and decisions that the operating team is supposed to follow up when faced with a particular situation.

 The operator action event tree has an initiating event and a final hazard. A node in the tree structure represents each task in this sequence. The possible outcome of the task is represented as ‘success’ or ‘failure’ paths leading out of the node. One of the hint sides of this method is that it does not account for alternate actions which could give rise to critical situations. In order to avoid these difficulties, a separate OAET must be created to model each particular action. Operator action event trees are used for the qualitative insights that are gained, and also as a basis for the quantitative assessment of human reliability (Embrey, 2003).

 The advantage of operator action event tree is that it is a logical method of structuring information regarding operator actions resulting from a particular initiating event. Also, it helps to identify the tasks which are essential in responding to the particular initiating event.

 The disadvantages of operator action event tree method are that it is not a satisfactory method for identifying diagnostic errors. Also, this method failed to address the error reduction or make any attempt to discover the main reason for the human errors represented. Furthermore, there is no assistance provided to ensure that the data used in the modelling process is complete and accurate. As a result, the comprehensiveness of the final operator action event tree will be a function of the experience of the analyst.

Goals, Operators, Methods and Selection rules (GOMS) Modelling: GOMS is a task analysis method that can be used to improve human-machine interaction and human performance by recognising and removing unnecessary actions. GOMS model breaks down the tasks into goals or subgoals. By analysis of goals, we can identify the cognitive or physical behaviours that an operator used to perform an operation. When a particular method is repeated during an operation, rules are applied to select a method which requires minimum effort and guarantees better safety (Gillan, 2012). A basic task analysis method is required prior to a GOMS analysis because it is essential to determine the goals before we use the method. After that, a GOMS model can be used to achieve the goals with the system being designed. GOMS modelling does not replace the most critical process in designing a sound system, that of understanding the user’s situation, working context, and overall goals (Kirwan & Ainsworth,1992).

 There are mainly four different types of GOMS concepts. They are CPM-GOMS, NGOMSL, Keystroke-Level Model (KLM), and CMN-GOMS. Even though all of these concepts provide predictive information about how individuals use computer systems, they all emphasise different parts of the task completion process. In choosing a GOMS concept to assess the design, one must know “the type of task the users will be involved in and the types of information obtained by applying the technique” (John et al. 1996). GOMS is used today to foretell issues with routine task behaviour. In a research study on mental workload and its impact on the pupillary response (Iqbal et al. 2004), a partial GOMS analysis of task completion time showed pupil size relates to changes in mental workload among subtasks. The research exposed from this GOMS model could help to “forecast a user’s mental workload” among smaller sub-tasks in a design. 

 Like any tool for measuring human behaviour, implementation of GOMS has its advantages and disadvantages. First, it gives both qualitative and quantitative measures, which can give powerful insight into how users will approach a design. A predictive model can be economically favourable because it finds ways to reduce execution time. With the high amount of experiments and research run on the GOMS model, we can confidently use the GOMS method to produce a sound production. It helps to discover usability problem, which cannot be found through any other forms of analysis. One of the disadvantages of GOMS is that it can only measure goal-directed tasks. This makes it not applicable in several cases. However, a GOMS model for a given design must be manually crafted by hand because no automation exists. The model must be constructed by someone who is already skilled in the applied GOMS concept. This makes GOMS both time and labour intensive. 

CONCLUSION

 Cranes are one of the essential types of equipment used in construction due to their vital role in performing lifting operations all over the construction site. The significant factors affecting the operation of cranes are project conditions such as blind lifts, overlapping cranes, length of operator work shift type of load, environmental conditions like wind, human factors like operator proficiency, operator character, signalperson experience and maintenance and safety management conditions (Shapira et al. 2012).

 The task analysis methods explained so far can be evaluated in terms of their focus on different aspects of the human-machine interaction. Nearly all task analysis techniques provide a minimum description of the noticeable aspects of operator behaviour at different levels of detail, together with some indications of the structure of the task. These are known as action-oriented approaches. Other methods focus on the mental processes which underlie observable behaviour, e.g. problem-solving and decision making. These methods are known as cognitive approaches. Among the three types of task analysis process discussed, Hierarchical Task Analysis and Operator Action Event Tree method come under the action-oriented approach, and GOMS method comes under Cognitive approach. From these analysis methods, GOMS method is more suitable for analysing the operation of cranes. Because the GOMS method describes a user’s cognitive structure on four components, but, GOMS start after a primary task analysis method. Hierarchical task analysis does not handle higher cognitive components of tasks, but, it permits the analyst to focus on crucial phases of the task, which can have an impact on crane operation. Therefore, Hierarchical Task Analysis and GOMS method can be used jointly as a framework for carrying out both action and cognitive task analysis. So, for the task analysis of the operation of cranes, a combination of HTA and GOMS method can be adopted.

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