Initial firing temperatures play an important role on the combustion rate of propellant. In gun propellants, initial temperature is a key factor for both accuracy and safety. Ideally, the initial temperature of the pr...Initial firing temperatures play an important role on the combustion rate of propellant. In gun propellants, initial temperature is a key factor for both accuracy and safety. Ideally, the initial temperature of the propellant should not influence the ballistic properties of the round. Nevertheless, constant initial temperature coefficients can not be achieved easily. This work focuses on the influence of the firing temperature on the ballistic properties, the mechanical integrity and the sensitivity to impact of nitrocellulose based propellants. Combustion rates have been determined by closed vessel tests. Ballistic properties have been investigated by firing 5.56 cartridges. The propellants have been conditioned at temperatures ranging from -54 ℃ to ＋71 ℃ before firing. The largest temperature coefficient is observed at high temperatures. The temperature sensitivity of the peak pressure in the combustion chamber can not be fully explained by the results from the closed vessel test. The authors speculated that the mechanical behaviour of the propellant grains at low temperatures influences also the overall ballistic properties of the round. Impact tests with propellants conditioned at low and high temperatures permit to investigate their mechanical strength under extreme temperatures and to better understand the propellant performance during firing. Tests on aged propellants have been conducted as well.展开更多
The apartment fire tests comprise a set of two full-scale fire experiments in a dwelling building made from pre-fabricated concrete elements in April 2013. Two apartments were nearly identically furnished and fully in...The apartment fire tests comprise a set of two full-scale fire experiments in a dwelling building made from pre-fabricated concrete elements in April 2013. Two apartments were nearly identically furnished and fully instrumented with thermocouples, video cameras and gas extraction probes. The apartments were ignited successively whereupon the fire in the second apartment developed freely to post-flashover conditions and got the main focus in this report. The apartment was completely furnished with contemporary furniture and objects, and had an average fire load density for residential occupancy. A full description of the fire load, ventilation conditions and instrumentation are provided. The focus of this report is primarily to obtain conclusions on the horizontal spread of smoke throughout the apartment during the fire growth period. Velocities of smoke spreading were measured to be in the range below 0.05 m/s which means that the smoke migrated over the longest distance throughout the apartment for about 3 to 4 minutes while the flame did not leave the initial fire room. The main aim of the experiments was to collect a comprehensive set of data from a realistic and contemporary fire scenario to validate numerical simulations.展开更多
Non-compliance with respiratory protection programs among firefighters may put them at increased risk of injury and illness from occupational exposures during fire extinguishing activities. This research aims to chara...Non-compliance with respiratory protection programs among firefighters may put them at increased risk of injury and illness from occupational exposures during fire extinguishing activities. This research aims to characterize respiratory protection practices among Florida firefighters. This information will allow better understanding of factors that are associated with non-compliance with respiratory protection guidelines. A survey questionnaire was used to characterize Florida fire departments in this cross-sectional study. Four hundred and seventy-seven surveys were administered to Florida firefighters both in person and electronically to collect information regarding firefighter knowledge and participation in their respective respiratory protection programs during the past twelve months. Survey questions were developed from the model set by the National Fire Protection Association (NFPA) which provides standards and regulations regarding firefighter protections. Summary statistics regarding firefighter department size, coverage area, and firefighter employment type were produced. Multinomial logistic regression analysis was performed to evaluate factors that impact respiratory protection programs. The 477 respondents were 91% male with a mean age of 39 years old (range 21 - 65 years). The majority of respondents, 76%, were non-smokers, 21% former smokers, and 3% current smokers. In regard to ethnicity, respondents were 77% Caucasian, 13% Hispanic, 3% African American, and 4% other. Most respondents were career firefighters, 97%, with less than ten years of experience, 44%, working in a fire department with at least 21 firefighters, 98%. Most respondents, 80%, had a written respiratory program in place. The most cited reason for not having implemented a written respiratory protection program was lack of knowledge related to the program. Multinomial logistic regression analysis of departments with response areas of at least 250,000 square miles produced a statistically significant 0.444 (0.219 - 0.901 CI) odds ratio for having a written respiratory program as compared to those with a less than 10,000 square miles response area. Additional resources need to be given to Florida fire departments to ensure that all firefighters receive adequate respiratory protection in accordance with NFPA guidelines. There is an association between fire departments with large response areas and non-compliance with respiratory protection guidelines in regard to: having a written respiratory program, the frequency of respiratory fit testing, and the frequency of medical fitness testing. This suggests that rural fire departments need additional resources to ensure firefighters are adequately protected. Additional research should focus on why these differences exist in the rural fire departments. Respondents stating a lack of knowledge or no requirement for a written respiratory program suggest that future efforts should focus on respiratory protection education and training.展开更多
为探明火灾下活性粉末混凝土(Receative power concrete,RPC)梁斜截面承载性能退化规律,设计制作了六根RPC简支梁试件,开展了恒载下ISO834标准火灾试验,获得了时间-位移曲线、荷载-位移曲线、内部温度变化、裂缝开展、破坏形态、高温爆...为探明火灾下活性粉末混凝土(Receative power concrete,RPC)梁斜截面承载性能退化规律,设计制作了六根RPC简支梁试件,开展了恒载下ISO834标准火灾试验,获得了时间-位移曲线、荷载-位移曲线、内部温度变化、裂缝开展、破坏形态、高温爆裂等数据,分析了剪跨比、荷载水平、配箍率、纵筋配筋率对火灾下RPC梁斜截面承载性能的影响规律。结果表明:剪跨比、荷载水平是影响RPC梁斜截面耐火极限的关键因素,剪跨比由2.5增至3.5,荷载水平由0.25增至0.45,RPC梁耐火极限可降低30 min以上;配箍率对RPC梁的斜截面承载力和耐火极限影响显著;纵筋配筋率对RPC梁耐火极限影响甚微。火灾高温、爆裂削弱了RPC梁的斜截面承载性能,爆裂导致内部材料直接受火,加速其力学性能劣化,使梁斜截面承载力降低33.5%以上。该研究可为火灾下RPC梁斜截面承载安全及火灾后加固修复提供参考。展开更多
文摘Initial firing temperatures play an important role on the combustion rate of propellant. In gun propellants, initial temperature is a key factor for both accuracy and safety. Ideally, the initial temperature of the propellant should not influence the ballistic properties of the round. Nevertheless, constant initial temperature coefficients can not be achieved easily. This work focuses on the influence of the firing temperature on the ballistic properties, the mechanical integrity and the sensitivity to impact of nitrocellulose based propellants. Combustion rates have been determined by closed vessel tests. Ballistic properties have been investigated by firing 5.56 cartridges. The propellants have been conditioned at temperatures ranging from -54 ℃ to ＋71 ℃ before firing. The largest temperature coefficient is observed at high temperatures. The temperature sensitivity of the peak pressure in the combustion chamber can not be fully explained by the results from the closed vessel test. The authors speculated that the mechanical behaviour of the propellant grains at low temperatures influences also the overall ballistic properties of the round. Impact tests with propellants conditioned at low and high temperatures permit to investigate their mechanical strength under extreme temperatures and to better understand the propellant performance during firing. Tests on aged propellants have been conducted as well.
文摘The apartment fire tests comprise a set of two full-scale fire experiments in a dwelling building made from pre-fabricated concrete elements in April 2013. Two apartments were nearly identically furnished and fully instrumented with thermocouples, video cameras and gas extraction probes. The apartments were ignited successively whereupon the fire in the second apartment developed freely to post-flashover conditions and got the main focus in this report. The apartment was completely furnished with contemporary furniture and objects, and had an average fire load density for residential occupancy. A full description of the fire load, ventilation conditions and instrumentation are provided. The focus of this report is primarily to obtain conclusions on the horizontal spread of smoke throughout the apartment during the fire growth period. Velocities of smoke spreading were measured to be in the range below 0.05 m/s which means that the smoke migrated over the longest distance throughout the apartment for about 3 to 4 minutes while the flame did not leave the initial fire room. The main aim of the experiments was to collect a comprehensive set of data from a realistic and contemporary fire scenario to validate numerical simulations.
文摘Non-compliance with respiratory protection programs among firefighters may put them at increased risk of injury and illness from occupational exposures during fire extinguishing activities. This research aims to characterize respiratory protection practices among Florida firefighters. This information will allow better understanding of factors that are associated with non-compliance with respiratory protection guidelines. A survey questionnaire was used to characterize Florida fire departments in this cross-sectional study. Four hundred and seventy-seven surveys were administered to Florida firefighters both in person and electronically to collect information regarding firefighter knowledge and participation in their respective respiratory protection programs during the past twelve months. Survey questions were developed from the model set by the National Fire Protection Association (NFPA) which provides standards and regulations regarding firefighter protections. Summary statistics regarding firefighter department size, coverage area, and firefighter employment type were produced. Multinomial logistic regression analysis was performed to evaluate factors that impact respiratory protection programs. The 477 respondents were 91% male with a mean age of 39 years old (range 21 - 65 years). The majority of respondents, 76%, were non-smokers, 21% former smokers, and 3% current smokers. In regard to ethnicity, respondents were 77% Caucasian, 13% Hispanic, 3% African American, and 4% other. Most respondents were career firefighters, 97%, with less than ten years of experience, 44%, working in a fire department with at least 21 firefighters, 98%. Most respondents, 80%, had a written respiratory program in place. The most cited reason for not having implemented a written respiratory protection program was lack of knowledge related to the program. Multinomial logistic regression analysis of departments with response areas of at least 250,000 square miles produced a statistically significant 0.444 (0.219 - 0.901 CI) odds ratio for having a written respiratory program as compared to those with a less than 10,000 square miles response area. Additional resources need to be given to Florida fire departments to ensure that all firefighters receive adequate respiratory protection in accordance with NFPA guidelines. There is an association between fire departments with large response areas and non-compliance with respiratory protection guidelines in regard to: having a written respiratory program, the frequency of respiratory fit testing, and the frequency of medical fitness testing. This suggests that rural fire departments need additional resources to ensure firefighters are adequately protected. Additional research should focus on why these differences exist in the rural fire departments. Respondents stating a lack of knowledge or no requirement for a written respiratory program suggest that future efforts should focus on respiratory protection education and training.
文摘为探明火灾下活性粉末混凝土(Receative power concrete,RPC)梁斜截面承载性能退化规律,设计制作了六根RPC简支梁试件,开展了恒载下ISO834标准火灾试验,获得了时间-位移曲线、荷载-位移曲线、内部温度变化、裂缝开展、破坏形态、高温爆裂等数据,分析了剪跨比、荷载水平、配箍率、纵筋配筋率对火灾下RPC梁斜截面承载性能的影响规律。结果表明:剪跨比、荷载水平是影响RPC梁斜截面耐火极限的关键因素,剪跨比由2.5增至3.5,荷载水平由0.25增至0.45,RPC梁耐火极限可降低30 min以上;配箍率对RPC梁的斜截面承载力和耐火极限影响显著;纵筋配筋率对RPC梁耐火极限影响甚微。火灾高温、爆裂削弱了RPC梁的斜截面承载性能,爆裂导致内部材料直接受火,加速其力学性能劣化,使梁斜截面承载力降低33.5%以上。该研究可为火灾下RPC梁斜截面承载安全及火灾后加固修复提供参考。
