Search the repository

A+ | A- | | SLO | ENG

Abstract: As thin-layer burning of fuels on water are often followed by thin-layer boilover fires, particularly during the firefighting process, an experimental and numerical study was undertaken to address key aspects of such fires, especially in plateau areas (i.e., sub-atmospheric pressure). In the thin-layer boilover experiments at sub-atmospheric pressure (69 kPa), diesel was used as the fuel in five circular steel trays (ranging from 0.4 m to 1.2 m in diameter) and a square steel tray (side length of 2.5 m). The burning process, and especially the continuous boilover stage, was presented and the corresponding boilover intensity, time to boilover onset and boilover time interval were measured and analyzed. The results show that the flame height increased sharply at the initial boilover, while this increasing range gradually became weak for the subsequent boilovers. The initial boilover intensity showed a linear dependency on the fuel layer thickness at the time of boilover, and the slope of the boilover intensity line decreased with increasing pan area. Eventually, the effect of pan area on boilover intensity became limit. Moreover, a predictive model for the boilover intensity was established based on dimensionless analysis. The initial boilover onset time under the sub-atmospheric pressure was delayed compared with that under atmospheric pressure. The corresponding predictive correlation (for 69 kPa) with different diameter and fuel thickness was developed based on the one-dimension two-layer conduction model. In the end, the boilover time interval decreased with the boilover times, closing to uninterrupted boilover eventually. This work enriches the thin-layer boilover behavior experimental data at sub-atmospheric pressure and provides guidance for the fuel storage safety.
Keywords: thin-layer boilover, boilover intensity, time to boilover onset, boilover time interval, sub-atmospheric fires
Published in DiRROS: 16.01.2024; Views: 190; Downloads: 42
Full text (1,04 MB)
This document has many files! More...

Abstract: A J-value assessment was carried out to quantify the costs and benefits of sprinkler system installation in car parks, both with respect to life safety and property protection. Nine scenarios were established based on collected input data. All car park types were considered for the USA, England, Scotland, Wales and the UK nations collectively, while separate considerations were made for multi-storey car parks (MSCPs) in the UK and for MSCPs, underground and other parking types in England. Even when assuming 100% sprinkler effectiveness, the J-values for the nine scenarios were all larger than unity (ranging from 5 to 555), thus indicating that the installation of sprinklers is not a cost-effective investment for car parks from a societal point of view. The analysis showed that different car park types must be treated separately, due to specifics of structure and fire statistics. The lowest J-values were obtained for MSCPs and underground car parks. Sprinkler installation mainly provides property protection benefits, because of property loss savings substantially outweigh those associated with life safety. Even though sprinklers were not cost-effective for car parks in the current analysis, the scarcity of data and new emerging technologies suggests that further investigation is needed.
Keywords: cost-benefit analysis, J-value, life quality index, Car parks, Sprinkler systems
Published in DiRROS: 09.01.2024; Views: 180; Downloads: 65
Full text (789,71 KB)
This document has many files! More...

Abstract: Concurrent flame spread data for thermally-thin charring solid fuels are presented from Saffire and BASS experiments performed in habitable spacecraft for three duct sizes, five sample sizes, two materials, and two atmospheres. The flame spread rates and flame lengths were strongly affected by duct size even for the relatively large ducts (> 30 cm tall). A transient excess pyrolysis length (i.e., flame length overshoot) was observed for the cotton fabric that burned away, which indicates that the transient excess pyrolysis length phenomenon is caused by more than just the flame moving into the developing boundary layer thickness as was the case with the SIBAL sample. A burnout time, defined as the pyrolysis length divided by the flame spread rate, normalized the pyrolysis length histories into a single curve with a steady burnout time of 22 s for the SIBAL fabric. The transient excess pyrolysis length is hypothesized to be a post-ignition flame growth transient for the essentially two-dimensional flames where the burnout time becomes very long until the preheat and pyrolysis lengths develop. The three-dimensional flames over narrow samples have lateral thermal expansion and lateral oxygen diffusion which allows them to transition to a steady state length without the transient excess pyrolysis length. Surface temperature profiles, nondimensionalized by the pyrolysis length, indicate that the temperature profiles exhibit the same shape across the pyrolysis zone. A surface energy balance calculation in the preheat region revealed that the heat flux increased rapidly at the pyrolysis front to near the critical heat flux for ignition. An estimate of the acceleration of the inviscid core flow in the duct due to thermal expansion and developing boundary layers on the duct walls and the SIBAL sample surface seems to explain the observed spread rate trends across three duct sizes and multiple sample sizes.
Keywords: concurrent flame spread, microgravity, duct size, sample size, cellulose fabrics
Published in DiRROS: 08.01.2024; Views: 186; Downloads: 38
Full text (2,13 MB)
This document has many files! More...

Abstract: The analysis of the current state of fire statistics and data collection in Europe and other countries is needed to increase awareness of how fire incidents affect buildings and to support pan-European fire prevention and fire mitigation mea- sures. The terminology and data collected regarding fire incidents in buildings in the EU Member States were mapped to obtain meaningful datasets to determine common terminology, collection methodology, and data interpretation system. An extensive literature review showed that fire data collection systems have been instrumental in informing firefighting strategies, evidence-based planning, prevention, and educational programmes. Differences and similarities between fire data collection systems were also investigated. The amount and quality of the information in fire statistical recording systems appear to be influenced by the complexity and structure with which the data are collected. The analysis also examined the existing fire statistics in the EU Member States and a few other countries. Finally, a detailed investigation of the number of fires, fire deaths, and injuries from 2009 to 2018 in several countries was examined based on data from a report by CTIF. The trends showed differences attributable to the existing fire statistical practices in terms of terminology and data collection, and interpretation. Part II proposes a common terminology for selected fire statistical variables. The results provide relevant information regarding fire safety at the European level and should be used to guide the development of more uniform fire statistics across Europe.
Keywords: fire statistics, fire incidents, fire statistical variable, terminology, data collection, data interpretation
Published in DiRROS: 13.11.2023; Views: 403; Downloads: 114
Link to file

Abstract: Diffusion flame behaviour and silica ash (SiO2) production were experimentally studied for various Polydimethylsiloxane (PDMS) membrane thicknesses (0.125 mm to 1.0 mm) in normal gravity and during microgravity flight experiments. The flames were established on vertical samples (300 mm in length) and subjected to either opposed or concurrent forced flows (both laminar and turbulent), assimilating the NASA Test 1 that is in use for spacecraft material selection. The opposed flame spread rate was observed to be steady and could be estimated using classical theory. Under concurrent flow, the flame spread rate was only steady for very high forced flows. The opposed flame-spread rate ranged from 0.5 to 1.5 mm/s, while the concurrent case ranged between 0.1 and 12 mm/s. The transport of silica ash (SiO2) was found to affect the heat balance of the concurrent flame spread in a manner that resulted in unsteady flame spread. For opposed flame spread, on the other hand, the transport of silica ash showed to be irrelevant. The extinction behaviour for the concurrent flame spread was heavily dominated by the transport of silica-ash, while for opposed flames, extinction was due to kinetics (at high forced flows). In microgravity environments, the transport and deposition of silica ash is anticipated to dominate flame spread and near-limit as well. These results suggest that silica-based products might be less flammable in microgravity than other similar materials such as common thermoplastics (PP or PE) used as wire jackets.
Keywords: silicone burning, spacecraft fire safety, flame spread, near-limit, silica-ash
Published in DiRROS: 13.11.2023; Views: 339; Downloads: 93
Full text (1,61 MB)
This document has many files! More...