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Again and again in case of a fire a bursting of acetylene cylinders occure. In the case of such a cylinder failure, these represent an enormous threat to fire and rescue services. BAM has been dealing for many years with the effects of acetylene cylinder failure. The presentation introduces BAM's experimental work in this area and outlines various options for action to reduce the risk for fire and rescue services. In the beginning BAM as well as the experimental possibilities at the BAM TTS are presented.
Acetylene pressure cylinders are widely used in the industrial sector for welding, flame cutting, or heating.
Sometimes during work, not only with acetylene cylinders, fires occur and in this case the risk of destruction increases and the behavior of such an exposed cylinder is unpredictable. The purpose of this study is to identify those critical conditions when acetylene cylinders burst and explode in fires. In the present study, acetylene cylinders were exposed to fire conditions. For this purpose, a woodpile as a source of fire was chosen, tested, and evaluated. In addition to the fire condition, this option guaranteed reproducibility and similar conditions for all tests. The individual cylinders were equipped with thermocouples measuring the shell temperature, and half of them were prepared in order to measure the temperatures inside the cylinder. An important factor was the measurement of the amount of pressure that was achieved during the destruction of the cylinder. For this purpose, a pressure transducer was attached to the outlet of the cylinder valve. Exposed to direct fire, they can explode in 10 min, which was confirmed. The critical pressure of 40 bar has been reached in 6 min, followed by destruction after 7 min in fire. Cylinders with internal thermocouples were destroyed when lower pressure was achieved. This confirms the fact that any change of the pressure cylinder affects the original properties. After the tests, the fragments of the selected cylinders were subjected to material tests. The results obtained in these tests are the main source of information for understanding the behavior of acetylene cylinders in fire and the possibility of increasing the safety of intervening rescue services in an emergency.
In this paper two different approaches for predicting the heating-up of an acetylene cylinder involved in a fire and the afterward cooling with water are presented. In the simulations polynomial functions were used to describe the temperature dependency of the thermal properties of the cylinder interior, which is a complex system composed by a solid porous material, a solvent (typically acetone) and acetylene dissolved in it. Model equations covered heat conduction in the cylinder interior and at its walls. In the first approach the cylinder surroundings were simulated as a further domain constituted by CO2, during the fire exposure, and for water, during the cooling. In this domain the coupled heat transfer (convection and conduction) and the momentum equation (Navier-Stokes) were solved. In the second approach no further domain was considered but boundary conditions were set directly on the cylinder walls. Results of the calculations performed with both approaches are presented. This work could prove helpful in predicting to which extent the interior of an acetylene cylinder exposed to fire reaches temperatures capable of initiating the decomposition of acetylene and to determine how long a water cooling should be applied, so that the system is brought again under non-critical conditions.
Prevention of the explosion of acetylene cylinders involved in fire: experiments and simulations
(2011)
In order to assess the effectiveness of water cooling of acetylene cylinders involved in fire, a total of 13 bonfire tests with 8.9-, 10
and 50-l-cylinders were performed. During the experiments the pressure
in the cylinder and the temperature at different locations within the porous material and on the Shell surface as well as the flame temperature were measured. Overall 8 burst tests were performed, in order to determine the times to explosion for the cylinders. Cylinders failed not later than 15 minutes from the ignition of the bonfire, often with generation of a fireball. During the other 5 tests, the fire was extinguished before the expected burst and the cylinder was cooled with water. In 2 of the 5 extinction experiments, the explosion of the cylinder could be prevented. Noticeably, in one case the on-set of the decomposition of acetylene had already been observed, before the cooling was started. In spite of that, the cooling was still effective. The interpretation of the current results and of the data from previous tests with 40-l-cylinder suggests that single acetylene cylinders involved in fire might be saved by cooling, if their pressure does not exceed a value of about 45 bara. The recorded values of pressure and temperature were used to develop and validate a mathematical model for the prediction of the heat transfer in acetylene cylinders during the exposure to fire and the afterward cooling. The predictions agreed well with the experimental results.
In this paper a mathematical model for predicting the heating-up of an acetylene cylinder involved in a fire is presented. In the simulations polynomial functions were used to describe the temperature dependency of the thermal properties of the cylinder interior, which is a complex system composed by a solid porous material, a solvent and acetylene dissolved in it. Model equations covered heat conduction in the cylinder interior and at its walls, while the fire surrounding the cylinder was simulated by solving the coupled heat transfer and the momentum equation. Results of the calculations and the effects of some model parameters are discussed.
Fire exposure tests of acetylene cylinders were performed. The purpose of the experiments was to gather information on the behavior in fire of such vessels, depending on the initial charge of acetylene. In fact "empty" acetylene cylinders still contain the solvent in which acetylene is dissolved plus the amount of acetylene to saturation at atmospheric pressure and ambient temperature and may still constitute a threat to safety. In the fire exposure tests performed the hazardousness of these vessels was demonstrated, since it was observed that not only fully charged acetylene cylinders but also cylinders with saturated solvent can explode, provided the heat transfer to the vessel is sufficient. The times to explosion were shorter for fully charged cylinders, due to the higher initial pressure and to the faster pressure increase. The effects of the explosions are comparable for both fully charged cylinders and for cylinders with saturated solvent, except for the smaller fireball which is produced in the second case, due to the smaller amount of fuel available. In both cases the cylinder walls or at least fragments can fly further than 100 m away from the burst location. Results of the experiments are presented in the paper. During the tests, temperature measurements at the cylinder walls and in the cylinder interior were performed. Furthermore, the pressure in the cylinder was recorded. The collected data will serve for the validation of a numerical model for the simulation of the heating of acetylene cylinders involved in fire and of the afterward cooling with water, which has been developed. The constitutive model equations and the results of some simulations are presented in the paper.