Abstract of Special Research Report (SRR-No.27)
National Institute of Occupational Safety and Health, Japan
Comprehensive Study on Preventive Techniques for Industrial Explosions in Chemical Processes
Introduction
SRR-No.27-1 |
Hidenori MATSUI |
: Many kinds of chemical substances are processed in industries. Industrial explosions and fires related to chemical processes have shown a tendency to increase since 1996 in Japan. Although, the rate of total number of occupational casualties caused by explosion and fire is not so high in the total occupational casualties, the number of serious accidents (more than three causalities) due to the industrial explosion, fire and poisoning shows the second highest rank next to the traffic accidents. Some results of the industrial explosions such as the accidental explosion of the hydroxyl amine distillation plant in Gunma prefecture and the accidental explosion of the hydrogen peroxide tank truck on the metropolitan expressway gave a great influence on the public. It is very important to assess the explosion hazards in chemical processes and to take preventive measures against accidental explosions caused by chemical substances.
Keywords; Chemical processes, Industrial explosions, Explosion hazard evaluation, Safety measures |
A Survey on Evaluation Techniques of Reaction Runaway Hazards in Chemical Processes
SRR-No.27-2 |
Takayuki ANDO, Yasuhiro FUJIMOTO and Mieko KUMASAKI |
: The thermal runaway process of chemical reactions is characterized particularly by a progressive increase in heat generation rate, temperature and pressure. It is initiated when heat generation from particular chemicals undergoing exothermic reaction or decomposition becomes greater than cooling capacity of facilities. |
Real Time Optimization of Reaction Parameter and Measurement Prediction
SRR-No.27-3 |
Teruhito OHTSUKA, Takaaki MIZUTANI, Ou-Sup HAN and Yasuhiro FUJIMOTO |
: The most important thing for safety is "precise prediction". But experiment under exactly same condition is impossible for almost all case. Therefore, various extrapolation is used for estimation. And factor of safety is also adopted without any explanation.
Keywords; Reaction parameter, Real time optimization, Measurement prediction, BFGS, Agee-Turner |
A New Prediction Method of Heart Releasa Rate for Heterogeneous Liquid-Liquid Batch Reactions with the Agitation Speed
SRR-No.27-4 |
Yasuhiro FUJIMOTO |
: Some industrial explosions, which occurred on the heterogeneous liquid-liquid reaction process, have been reported. To progress such reaction smoothly, reactants need to be mixed well by mechanical agitation. And it is the failure of controlling the mixing that causes unusual reaction and sometimes leads a runaway situation. |
Propagatation Behavior and Mechanisms of the Dust Flame in a Duct
SRR-No.27-5 |
Ou-Sup HAN, Masaaki YASHIMA and Toei MATSUDA |
: The aim of this study is to investigate experimentally the flame structure in dust flame propagation and to provide the fundamental knowledge for development of explosion suppression systems applied to dust explosions. Insufficient information on dust flame propagation is mainly due to experimental difficulties in the generation of a uniform dust suspension, as well as the fact that particle size and size distribution. Upward propagating laminar flames in a vertical duct of 1800 mm height and 150 mm × 150 mm square cross-section are observed. From the experimental result, it is found that propagating lycopodium flame front shows the double flame structure in which individual burning particles and ball-shaped flames surrounding several particles are included. The thicknesses of preheated and reaction zone have been also determined by a schlieren photography. The flame in spatial area between independent flames and individual burning particles is not observed. This means that the flame can not propagate continuously in comparison with premixed gaseous flames. The thickness of lycopodium dust flame is observed to be 20 mm, about several orders of magnitude higher than that of premixed gaseous flames. By means of the microscopic visualization, it was found that the flame front propagating through lycopodium cloud is discontinuous and not smooth. The experiments using a PIV (Particle Image Velocimetry) system with a high-resolution video camera have been conducted to clarify the motion of particles during the flame propagation. Due to convective flow induced by the flame, a part of gravitational settling particles is shifted to its surrounding sides and the rest of the particles changed their movements to upward in front of the flame. Such particles movement causes a dynamic variation in dust concentration ahead of the flame, which propagates at lower dust concentration rather than the mean concentration. Considering the movement of single particle ahead of the flame, a certain residence time of the unburned particle in preheat zone is needed to generate combustible gas from the particle. The residence time will depend on preheat zone thickness, particle velocity and flame propagation velocity. |
Suppression of Dust Flames Propagating in a Duct (Quenching with Water Sprays, Wire Gauze and Isolation by Inert Gas)
SRR-No.27-6 |
Masaaki YASHIMA |
: It is necessary to conduct protective measures for ignition prevention in powder handling processes since ignition may cause dust explosions or fires. Moreover explosion protection and explosion suppression systems are also required so that the damage may not expand even ignition occurs. Explosion pressure release (vent for deflagrations), automatic fire extinguishing systems and rapid valves (mechanical isolation and chemical isolation) have been known as equipment to mitigate the damage of dust explosions. The goal of this study is to develop a new explosion suppression system applied to dust explosions, which relates to the latter two terms of equipment described above. An experimental study has been conducted to obtain fundamental knowledge on suppression of dust flames in a duct by (a) water sprays, (b) wire gauges and porous plates, and (c) inert gas isolation. Lycopodium was used as a sample powder to compare with previous studies. Experiment(a):The experimental apparatus consisted of a vertical duct having 200 × 200 mm in square cross section and 3 m in height, a fluidized bed and a water spray system. Lycopodium was mainly used at the concentration of 50 g/m3, which is lower than the stoichiometric concentration for the dust cloud. An infrared sensor was mounted on the surface of the duct to detect the propagating flames and made water spray with time delay. Experiment(b):The experimental apparatus consisted of a vertical duct (pipe) having 60 mm in diameter and 1.1 m in height, a fluidized bed and a mechanical insert system of quenching elements. Different sizes of wire gauzes with more than 0.46 mm opening and porous plates were used as quenching elements. In order to examine quenching behavior of the flame, the quenching elements were rapidly inserted into the duct from horizontal direction before arrival of the flame at the element position but after a spark ignition was given. Experiment(c):The experimental apparatus is similar that of Experiment (b) except for the injection system of inert gas from the duct wall. Argon (Ar) was used as inert gas. Principal results are as follows :
|
The Evaluation of Insulation in a Method Wiring Board by the Monitor Using Wiring Board of the Comb-pattern
SRR-No.27-7 |
Tatsuo MOTOYAMA |
: Recent progress on wiring boards has made them more weather-resistant, and narrow pitched wiring boards have been used in severe environments, such as chemical processes, for instrumentation and control equipment. Such equipment is vital for production systems, and related maintenance problems can spread to other parts of a system and increase the risk of an industrial accident. The failure in wiring board is generally caused by loss of conductivity of wire and loss of insulation between wirings. The causes of loss of insulation are primarily dust adhesion, electrochemical migration, and aging of polymers. Loss of insulation is greatly dependent on environmental factors. The evaluations of insulation between wires can be accomplished satisfactorily in electric power fields; however, no adequate technique exists for use in printed wiring boards. In a mounted wiring board, it is technically difficult to apply the methods mentioned above to the evaluation of loss of insulation since electronic components and elements are mounted between wirings. |
Basic Requirements and a Construction Method for a Gas Detection System with Asymmetrical Failure Characteristics
SRR-No.27-8 |
Tsuyoshi SAITO, Hiroyasu IKEDA and Noboru SUGIMOTO |
: Gas detection systems in chemical plants are utilized for many purposes, e.g., to prepare material gas, to control process reactions, to monitor product quality and so forth. In a case that a gas detection system is used as a safety interlock system, which compels the plant operation to stop when it detects the leakage or the accumulation of flammable or toxic gas into the work environment, its structure must be essentially different from other systems so that its failure never causes an accident even if it causes false trips. The gas detection system with such asymmetrical failure characteristics, however, still has not been developed because it is basically impossible to generate the energy of sensor signal output from the state that objective dangerous gas does not exist in a monitored area atmosphere. |
Safety Control Design and Safety Evaluation for Computerized Plant System
SRR-No.27-9 |
Hiroyasu IKEDA, Tsuyoshi Saito and Noboru SUGIMOTO |
: With advancement of large-scaled plants, the use of a computer increases in the control, and there is a tendency that programmable equipment including a micro-processor is introduced into a hardware safety related system based on conventional electromagnetic relays. Because reliability of normal hard-wired system is low, and a fault diagnosis capability is uncertain and insufficient, it is a trend to replace the hard-wired with a flexible and functional software. However, as for such a programmable controller, indistinct characteristics remain in the use in safety security still, and, for example, potential systematic failures which can not be identified may appear and cause unsafe conditions. |
Development of the Chemical Process Accident Database
SRR-No.27-10 |
Haruhiko ITAGAKI |
: An explosion and a fire often happened recently in the chemical processes. Worker's casualties and great damage arose due to such accidents. To prevent an explosion and a fire, it is required to develop the advanced safety technology corresponding to recent technological innovation and working conditions such as an advanced safety countermeasure, fail safe technology, and to diffuse the safety |
Development of the Support System for Prevention of Explosions at Chemical Processes
SRR-No.27-11 |
Haruhiko ITAGAKI |
: Explosion and fire often happen at the chemical plant. A search for the problem, the selection of the effective countermeasure and accurate cause study are very useful to prevent these accidents. The chemical process accident database based on the accident information provided by the Ministry of Health, Labour and Welfare was created, and accidents were analyzed in the National Institute of Industrial Safety. However, there is a little useful literature when a countermeasure to the specific device is selected at the factory. Therefore, the cooperation of the specialist who has knowledge and an experience is often necessary. So, the software named "Support system for prevention of explosions at chemical process" for the purpose of the support of the clarification of the explosion hazard and the cause investigation at the chemical process plant was developed. This system is composed by the chemical process accident database, the countermeasure database of chemical process accident and the program which refers to two databases. The main targets of this system are the business worker and the safety manager who are not a specialist of the safety. This system searches the accident cases which contains input search words at a moment. Then, this system shows the statistic of the countermeasure with the ignition source, the cause and other factors. This report was mentioned about the frame of the support system for prevention of explosions, the contents of the countermeasure database and the interactive search program. |