Daniel T. Gottuk

The Development And Mitigation Of Backdrafts: A Full-scale Experimental Study

An experimental study of the development and mitigation of backdrafts shows that the key parameter for backdraft development is the fuel mass fraction. The results reveal that the critical fuel mass fraction, Yf, required for the development of diesel fuel backdrafts is 0.16 for fully vitiated conditions. Analysis of the data in conjunction with results in the literature has also demonstrated that standard flammability diagrams can be used to predict bounding limits and trends on Yf with respect to other key variables, such as oxygen concentration. The injection of water spray was shown to be an effective mitigating tactic that was able to completely suppress backdrafts. The analysis reveals that backdraft suppression occurred primarily by means of diluting the atmosphere and reducing the fuel mass fraction, consistent with the critical Yf criterion, rather than by a thermal mechanism of cooling.

Alarm Thresholds For Smoke Detector Modeling

Models have been used to estimate smoke detector alarm times by calculating smoke optical densities resulting from fires and correlating the smoke value to an alarm threshold of the detector. This work evaluated the use of smoke optical densities outside a detector as criteria for predicting smoke detector responses. Results are presented for optical density alarm thresholds corresponding to when 20, 50 and 80 percent of the detectors had alarmed in full-scale tests. The data showed that there was a large amount of variability in the measured smoke optical density values outside a detector at the time of alarm. Major variables evaluated included detector type, fire type and nominal detector sensitivity. This evaluation also examined experimental smoke optical density data at the time of detector alarms and compared these smoke values to alarm thresholds recommended in the literature.

Smoke Transport and FDS Validation

A 2006 Fire Protection Research Foundation (FPRF) project used the NIST Fire Dynamics Simulator to investigate smoke detector spacing for spaces with deep beam pockets and level ceilings. One configuration evaluated in this research was a corridor configuration with varying beam depth, beam spacing, corridor width, and ceiling height. A subset of the modeled corridor configurations was conducted with full-scale experiments to validate the findings of the modeling study. This paper presents the findings of the experimental validation and new discoveries regarding smoke production and loss mechanisms that have an impact on modeling of fires and the spread of smoke. The temperature and velocity measurements along the corridor ceiling were consistent with the modeling results. However, the study showed that FDS significantly over-predicted smoke concentrations compared to the experiments. Exploratory findings indicate that soot deposits to the ceiling above the plume may be as high as 37 percent of the soot produced. Current versions of FDS do not account for this substantial soot loss. The work also revealed that there is a large discrepancy between reported small-scale soot yields and larger scale fires.

Multi-sensory, Data Fusion Detection System for Improved Situational Awareness

A multi-sensory approach is being used to develop new detection capabilities for improved damage assessment and real-time situational awareness. The detection system combines surveillance camera video images with selected spectral and acoustic signatures and image recognition technologies to provide a broad range of situational awareness. Various spectral and acoustic signatures, new video imaging techniques, and image recognition methods have been investigated and integrated into a multi-sensory prototype system. The prototype system is able to detect event signatures within the volume of a space (i.e., a “volume sensor”) rather than relying on spot-type fire detectors. Two prototype systems were built and assessed in full-scale testing aboard the exUSS Shadwell side-by-side with two commercial video image fire detection systems and several spot-type fire detection systems. Tests included a wide range of fire and nuisance sources, plus flooding and pipe rupture scenarios under actual shipboard background conditions. The prototype systems are shown to outperform the commercial fire detection systems for flaming and smoldering fires with a high level of nuisance immunity. In addition, they successfully detected the pipe ruptures and flooding scenarios. The system can be adapted for homeland security.