STOP BASEMENT FLOODING NOW

In designing our systems to be reliable, we employed Probabilistic Risk Assessment (PRA) analysis methods to determine the most likely causes of system failure and to determine the best ways to reduce those likely failures.  To perform the analysis, the following steps are performed:

Create a Computer Model

In performing the analysis, a computer model called a fault tree is created to represent all the different ways that a given system can fail.  Figure 3 shows a sample of the fault tree logic for a sump system.

 Figure 3: Sample Fault Tree Logic

Quantify the Risk for the System

The fault tree is used to quantify how frequently a system may fail using available industry data sources containing the failure rates of different components (pumps, valves, switches, etc.).  The computer model defines all the possible ways that a system can fail and the likelihood of failure.

Improve the System Design

The fault tree analysis identifies the most likely causes of failure of the system.  The system design is then improved to eliminate or reduce the likelihood of these critical failures.  The fault tree is updated with the proposed design changes and re-analyzed to determine the improvement in system risk.

Flood Frequency

Once the design process is completed, the results of the fault tree model can then be used by the consumer to judge which system is needed to attain a comfortable level of risk.  We report these flood frequency results on our System Comparison page to give the consumer something better than the typical "Good, Better, Best" evaluation of system performance.

Uncertainty

There is uncertainty in all risk assessment calculations, so we report a range of flood frequency values for each system: High Estimate, Best Estimate, and Low Estimate.  Important uncertainties include annual variations in weather, variations in drainage from one property to the next, and failure rate uncertainties.  The consumer can use their own personal history in their home to judge where they may fall in reported ranges.

Last modified: 05/22/08