Logical Models for Quantification of Occupational Risk: Falling from Mobile Ladders (PSAM-0058)


The Workgroup Occupational Risk Model (WORM) project in the Netherlands aims at the development and quantification of models for a full range of potential risks from accidents in the workspace. The project is part of a larger initiative to reduce the number of accidents their consequences by a significant degree.

Functional Block diagrams and their equivalent event trees are used to delineate the various accident sequences that might lead to injury or death consequences. A general functional block diagram has been developed where the undesirable safety consequence is decomposed to “Dose” and “Dose/Response”; “Dose” is decomposed to “Center Event” and “Mitigation”; “Center Event” is decomposed to “Initiating Event” and “Prevention”.

This decomposition when set in a diagram format produces a graph with “left to right” logic where the outermost left event is the Initiating Event which when coupled with the general event “Prevention” obtains the joint event “Center Event”. The Center Event when combined with the “Mitigation” event provides the joint event “Dose” which finally when combined with the event “Dose/Response” provides the overall “safety-consequence” event. When viewed this way the graph is sometimes called a “bowtie” diagram.

The methodology is demonstrated with an application to the risk of falling from a mobile ladder. Prevention from falling is provided by three other safety functions providing ladder strength, ladder stability and user ability. Further decomposition provides additional supporting measures. The resulting Functional Block Diagram and the corresponding event tree are presented and quantified.

  • Summary/Abstract
  • Introduction
  • Functional Block Diagram for Falls from Mobile Ladders
  • Quantification of the FBD
  • References

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