Technique for Human Error Rate Prediction (THERP)

Human Error Analysis recognizes and impacts possible human errors, or identifies the source of human errors found. The technique for human error-rate prediction (THERP) is a technique used in the human reliability assessment (HRA)

With the aim of eliminating errors, the Sandia Corporation created a tool to measure the probability of employee error in production operations.

The approach is based on the theory that it may be difficult or impossible to predict non-repetitive or infrequent acts, but it is possible to analyze repetitive actions to calculate human error probability data.

For selected tasks, THERP defines a Basic Error Rate (BER) that uses statistical methods to define valid human error rates when performing the task. The BER unit per million operations is a mistake.

Technique for Human Error Rate Prediction (THERP)


This data on the rates of human failure is of interest to safety specialists. For Fault Tree Analysis(FTA) and Event Tree Analysis (ETA) it is useful. The data is a mean average and may not be applicable to the operator in question. Fewer errors can be made by professional operators.

STEPS OF THERP 

  1. Define the system failures of interest. 
  2. List and analyze the related Human operations. 
  3. Estimate the relevant error probabilities. 
  4. Estimate the effects of Human errors on the system failure events. 
  5. Recommend changes to the system and recalculate the system failure probabilities.

ADVANTAGES OF THERP 

  1. Easy to use 
  2. Modest cost 
  3. Tabulated values reduce need for Analyst judgment 
  4. Selection rules reduce variability in results 
  5. No specialized software needed

LIMITATIONS OF THERP

  • Excessive emphasis on procedural details
  • Detailed models mask true causes for errors
  • False confidence that analyses are very precise
  • No structured input from Plant Personnel
  • Limited use for understanding important issues and
  • recommending improvements