Flashover

Aim: This article describes events, which occur during the development of a fire inside buildings. Special attention is devoted to the development of backdraft and flashover. Additionally, the article identifies possibilities for earlier prediction of potential developments based on symptoms and data from sensors. Furthermore, the article highlights a need to build a system, which supports commanders at the scene of an incident. Introduction: Extreme fire behaviour such as ventilation induced flashover, backdraft, and gas ignition or smoke explosion, pose significant threats to human life and property. A factor contributing to the significant risk for firefighters is associated with the rapid increase in the rate of heat release and temperature within structures. Based on data gathered from a reconnaissance, it is difficult to predict the probability of above mentioned events happening. Therefore, there is a need to devise a system with the potential for prediction of extreme fire behaviour, based on sensor data derived from premises engulfed by a fire. Such a system will undoubtedly be a useful tool, which will enhance the effectiveness and safety of firefighters. Furthermore, such a tool will support incident commanders in decision making and allow for the elimination of decisions, which could lead to development of flashover or backdraft.
Methodology: The study utilised two scientific approaches: review and critical analysis of literature, which provided an exit point and source of verifiable scientific hypotheses. This was enhanced by survey methods based on a contrast of current knowledge identified in literature with practical know how of experienced commanders from the Polish State Fire Service.
Conclusions: Non-linear progression and unpredictable fire behaviour, when it occurs, creates significant dangers to firefighters. Development of a system, which can analyse current sensor data gathered at the scene of a fire incident, will allow for the anticipation of extremes in fire progression with a consequential impact on safety. Such a system could function on the basis of data obtained from sensors as well as from information gathered during a reconnaissance - a firefighter could enter data manually, thus maximising the use of the system potential.

Conductors, insulators and semiconductors behave differently in the environment containing charged particles. For any sample substrate which consists either of these two or more has a specific charging property. In the charged environment, differential potential is built up on metal and insulators kept adjacent to each other. If the surface potential exceeds the specified threshold voltage, a breakdown occurs on the substrate's surface which results in to release of heat and light energy. This is termed as an electrostatic discharge or an arc. Thus discharges deteriorate the surface properties of the substrate and reduce its functional life. Hence understanding of such charging-arcing phenomenon on various substrate's surface is essential. For this purpose, a dedicated facility for creating charged environment using electron gun and plasma source is developed and various parameters of discharge are measured and analyzed. As the size of the substrate is an major concern of performing experiments, an algorithm for predicting arc current waveform is developed simultaneously. This software is based on the basic details provided by the user. Software is capable of generating a library of arc current waveforms on each arc favorable location. A dedicated database is obtained for each substrate having different geometrical shape. Generated arc waveform at any specified location is a function of its distance from substrate's edges. It is based on 'arc image pixel manipulation technique'. Both experimental and simulated results are obtained for smaller sample substrates initially. Software generated waveform and actual waveform are quite comparable with each other. On successfully identifying arc location on the surface using the algorithm, use of CCD camera for the same can be avoided. A unique approach for reproducing a different waveform at each location by breaking the symmetry of the substrate is also discussed in the paper. Index Terms-ESD on composites, arc current behavior, current location predictor, LabVIEW.

This work presents a study aiming to analyze the development of parallel discharges on insulating surfaces of different sizes uniformly polluted. Moreover, it is aimed to find an equivalence between multiple point-point and plane-plane configurations. The study is carried out under alternating current (AC) voltage. The effects of many parameters on the electric strength of the considered air gap system configurations are presented. These parameters are the length of the creepage distance, the pollution degree and the contaminated surface width. Glass rectangular surface are used for the tests. Finally, a video camera system is used to support this investigation by laboratory observations of the full process of flashover mechanism. The obtained results show that there is a width limit approximately equal to 8 cm beyond which several arcs, parallel, consecutive and independent can develop. This limit represents the minimal electrical performance of the insulation and we did not observe any effect of the volume conductivity on it.