Erin P. Collins

HRA for detection and suppression activities in response to fire events

This study consisted of a qualitative and quantitative evaluation of fire detection and suppression capabilities in a facility by the standard operating crew. This evaluation was made using Human Reliability Analysis (HRA) quantification techniques, which resulted in a set of human error probabilities (HEPs) characterizing the detection and suppression actions. The HEPs were input to a comprehensive event tree model that integrated the different detection and suppression activities into sequences of events (i.e., fire scenario outcomes) that were also probabilistically quantified. Based on the study findings, the following conclusions were made: 1. The overall method proved to have significant merit for conducting an initial scoping evaluation of fire detection and suppression probability by crew members, including automatic detection and facility modification influences. 2. The majority of the HEPs were constant (i.e., did not change) for different system window values. However, for relatively short system windows, key “manual” detection and suppression activities may fail. These insights suggested areas of the facility where fire protection improvements could be beneficial. 3. Better characterization of the timing associated with human actions is necessary. Historical data should be investigated to re-assess the timing and support the probability distributions and corresponding parameters selected for representing the time values. 4. Better characterization of the fires. The analysis preliminarily considered “slow” and “fast” growing fires. However, no explicit treatment was given to small fires that are easy to suppress or larger fires that may not be easily suppress. Further characterization of the probability of fires that can overcome the available suppression capabilities should be incorporated into the analysis. 5. Better characterization of system window times. A combination of historical data and detailed fire modeling analysis of selected fire scenarios should be applied since overall system window times were assumed and not based on an analytical characterization of specific fire scenarios. 6. There was an inherent assumption that the fire could be suppressed by the crew given the training and equipment available. Further analysis should be done to address fires with the capability of growth and propagation that can overcome the available suppression capabilities.

The Value of a Space Precursor Analysis Program: A Saturn Example

There is general agreement that “near miss” or “close call” data is valuable to the space program and whenever NASA becomes convinced that such events have occurred they have acted responsibly and quickly to address them. The problem lies in defining what constitutes a near miss in a system that is inherently very complex, such that ‘abnormalities’ are actually normal occurrences, and yet one that is relatively reliable because of the inherent strengths incorporated into the design, such as robustness, redundancy, and functional diversity. The question becomes: what would the consideration of failure precursors add to the insights to be drawn from history as it relates to forecasting future performance? This paper will use the example of the Saturn program to address the problems involved in forecasting the risk in complex, yet reasonably reliable programs and to indicate preliminary approaches for use in establishing a space industry precursor program.© 2003 ASME