Case studies included in a new book from the Center for Chemical Process Safety, "Guidelines for Safe Automation of Chemical Processes," provide examples of how errors by operators and maintenance personnel contribute to process safety incidents. A process upset can rapidly escalate from an annoyance into a highly stressful event for the operator, who is trying to get the process back to normal, and for the maintenance technician, who is trying to figure out what is going wrong with the control system.
The operator is often the first and last line of defense when processing equipment fails to perform. Operators need to understand the fundamentals of how the process reacts to both normal and abnormal situations, despite the use of advanced and increasingly remote automation systems. Operators also need to be able to rapidly respond as required during event propagation to recover the process, prevent loss of containment or support emergency response. Operator procedures and controls create a culture of disciplined adherence to safety practices. Critical tasks should be covered by detailed procedures.
The likelihood of error is impacted by the stress being experienced, but also by unique site characteristics. Poor management of bypasses and unplanned manual operation can place multiple critical tasks at risk simultaneously. Safety culture and organizational discipline impact the entire site's ability to sustain zero loss events. Plant personnel typically interact with multiple functions and systems across a site, so human error can be a contributor to coincident failures in what appear to be independent systems. Site-wide problems are referred to by reliability analysts as systematic, because the management gaps that allowed the errors to occur and to remain in-service are often institutionalized in the way things are done at a site. These errors will be committed again and again until site practices are changed.
The human factor characteristics of engineering, operations and maintenance cannot be eliminated. Human error can happen at any time, so it is necessary to have a rigorous approach to reduce its potential. Error reduction strategies are applied to scenarios where human errors can lead to significant process deviations or safeguard failures. Human factors significantly impact the operator's ability to respond as required when necessary. Human performance shaping factors should be considered when:
- Implementing the alarm management program.
- Estimating human response time.
- Estimating the operator likelihood of failure.
- Designing response facilities.
- Writing operator procedures.
- Training operators.
- Assuring competency.
Making effective use of control system technology while guarding against potential sources of systematic failure, whether due to hardware, software or human error, is critical to safe operation. Human factors should be considered during design, specification and procedure development. One key objective is to ensure situational awareness. Most operators are entirely reliant on their operator interface to provide situational awareness and to combat confirmation bias. Connecting two-dimensional operator interfaces to unit operational principles can be a training challenge in facilities without operator training simulators.
The challenge is to design integrated control and safety systems with strong consideration for human factors so the system performance can be sustained throughout the life of the process. Automation should be designed to be resilient to expected human errors and provide support for good decision making. The clarity of instructions, warnings and diagnostics is critical to successful error trapping and process recovery. Administrative and monitoring processes are needed to identify and correct errors that can happen. Safe automation considers how the operator will use the system under normal and abnormal conditions and seeks to reduce the likelihood of human error.
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