Human Reliability Analysis (HRA)
Quantified human error probability that defends your LOPA, QRA and safety case credit claims
Human Reliability
Analysis (HRA)
Human reliability analysis quantifies the human error probability for your safety critical tasks, typically somewhere between one in ten and one in a hundred thousand, so that we can anchor the operator credit in your LOPA, the initiating event frequency in your QRA and the human barrier effectiveness in your Bow Tie. The methods fall into three generations. The first generation is behavioural, led by THERP with its detailed task decomposition. The second generation is cognitive, led by CREAM and ATHEANA, which bring in common performance conditions and the surrounding context. The third generation is Bayesian and contextual, led by Petro HRA and IDHEAS, which are tailored to oil and gas and to modern control rooms. The HSE human factors guidance HSG48, the CCPS human factors methods and the ISO 11064 control room ergonomics standard frame the discipline. The common review failures are easy to spot, namely the indiscriminate use of HEART nominal probabilities without proper selection of performance shaping factors, the double counting of operator credit between LOPA and the safety instrumented system, and the neglect of time pressure and stress in upset scenarios, and we guard your analysis against all three.
How the study is executed
A structured, facilitated process that runs from scope definition through close out and produces defensible, actionable outputs.
Identify safety critical tasks from HAZOP, LOPA, operating procedures, and incident history, rank by consequence severity and frequency of demand, define HRA scope and method selection basis, agree boundary between HRA scope and nominal operating procedure design.
Decompose each safety critical task to atomic action steps using HTA, document goals, sub goals, operations, and plans, identify decision points, information requirements, feedback loops, and time constraints, provide structured task description for HEP calculation input.
Select method per task type and complexity, HEART for screening, THERP (NUREG/CR 1278) for detailed decomposition, CREAM for cognitive tasks, Petro HRA (IFE 2017) for process industry context, IDHEAS G for nuclear grade, calculate nominal HEPs per method tables.
Calibrate Performance Shaping Factors (THERP) or Error Producing Conditions (HEART) to plant context, time pressure, stress, training level, HMI quality, procedure clarity, communication quality, environmental conditions, distinguish Error of Omission (EOO) vs Error of Commission (EOC).
Apply THERP dependence modelling (zero to complete) to sequential operator actions, calculate combined task HEP accounting for complete dependence, compute recovery factors for actions that can be corrected by a subsequent check, prevent operator double credit against LOPA SIF.
Integrate calibrated HEPs into LOPA operator IPL credit and QRA initiating event frequency, issue Bow Tie human barrier effectiveness scores, produce HMI, alarm rationalisation, and procedure improvement action register, provide competency and refresher training prescription ranked by HEP priority.
What the study covers in full
Outcomes of Human Reliability Analysis (HRA)
- We quantify the human contribution that drives sixty to eighty percent of major accident causal chains
- We surface the over credited operator protection layers that fail under realistic time pressure and stress
- We drive HMI, procedure and alarm redesign at the points that actually matter
- We anchor your competency programmes against the tasks with the highest error probability
- You satisfy the IEC 61511 Clause 9 human factor requirement for operator credit in LOPA
- Your operator action claims withstand HSE, CSB and OSHA national emphasis programme scrutiny
- You gain a human factor demonstration for your COMAH safety case
- Your work aligns with ISO 11064 control room design and HMI ergonomics
- We steer your DCS HMI graphics design toward situation awareness under ISA 101
- We target alarm rationalisation under ISA 18.2 at the genuine cognitive bottlenecks
- We anchor your operating procedure rewrite, especially the abnormal and emergency chapters
- We inform your shift handover protocol design and fatigue risk management
- We prevent the LOPA over credit pattern that drives a later safety instrumented system retrofit
- We reduce near miss frequency through realistic procedure and HMI design
- We target your training spend at the ten to twenty percent of tasks with the highest error probability
- We trim your underwriter loadings where you can document human factor maturity
Codes & standards we work to
Triggers that signal the need
Where Human Reliability Analysis (HRA) applies
Wellheads, separators, gas compression, FPSO topsides, produced water systems.
Distillation columns, reactors, heat exchangers, storage spheres, LPG handling.
Cryogenic exchangers, liquefaction trains, BOG compressors, storage and sendout.
Reactive systems, batch reactors, solvent handling, runaway reaction scenarios.
Boilers, HRSGs, steam headers, hydrogen systems, ammonia SCR units.
Sterile vessels, CIP/SIP, pressure fermenters, solvent recovery, spray dryers.
Tangible deliverables
- A report with the method selection rationale and the error probability table
- A safety critical task analysis register with criticality ranking
- Hierarchical task analysis worksheets for each critical task
- A performance shaping factor calibration record for each task
- An integration map of the error probabilities into your LOPA, QRA and Bow Tie
- An action register for HMI, alarm and procedure improvement
- A competency and refresher training prescription
- A recovery factor analysis for sequential actions
Ready to start your project?
Speak with our team to scope an engagement tailored to your facility, regulatory context, and lifecycle stage.