이산화탄소 소화설비에서 누출로 인한 질식사고의 원인분석과 대책에 관한 연구

Abstract

A Study on the Cause Analysis and Countermeasures to Asphyxiation Accidents Due to the Leakage from Carbon Dioxide Fire Extinguishing Equipment

Ho-Jung Kang

Dept. of Interdisciplinary Program of Fire Protection and Disaster Prevention Engineering, Graduate School, Pukyong National University

Abstract

1) In this study, the quantity of carbon dioxide leaked from the detached selector valve and the pressure changes during the leakage process were analyzed using the ID transient analysis on the system line of carbon di-oxide fire extinguishing equipment, and through the simulation of carbon dioxide diffusion using the computational fluid dynamics, the diffusion pa-th, the oxygen-carbon dioxide concentration at the operator's position and the effect caused by the pressure generated at the time of leakage were analyzed. Based on these, the carbon dioxide leakage process were analy-zed, and the results are as follows.

(1) Due to the pressure of carbon dioxide released into the gas collection pipe room, the upper part of the outer wall of the gas collection pipe room made of gypsum board was damaged, and thus, CO2 was leaked into the adjacent passage. Subsequently, the oxygen concentration at the operator's position was reduced to minimum 5.3%, resulting in the asphyxiation accident due to the lack of oxygen.

(2) The cause of the carbon dioxide leakage from the carbon dioxide fire extinguishing equipment is as follows. The locking pin, a countermeasure to prevent CO2 leakage, was partially installed due to the replacement work of the old automatic fire detection system, but upon receiving a false signal, the starter solenoid valve of the electrical room on the other floor was activated, which led to the release of CO2.

(3) The cause of the detachment of the selector valve is as follows. As the dimensions of the female and male threads did not match, the approximately two threads were not fastened. During this process, the O-ring was detached, which weakened the strength of the joint further, and thus, the bolted part could not withstand the pressure of CO2, resulting in the detachment of the selector valve. (4) The ID Transient analysis, upon the assumption that the maximum pressure was 3.6 MPa and the atmospheric pressure 600 kPa at the position of the detached selector valve at the time of the accident, showed that the amount of carbon dioxide leaked from the exit port of the valve and that released from 2 open valves were similar, with a mean error of 15%.

(5) In order to analyze the diffusion process of leaked carbon dioxide, FLACS v10.7 program was used, and the analysis of the oxygen concentration showed that it was 10% or less at the position of the operator at 25 seconds from the leakage of carbon dioxide and reduced to the minimum of 5.3% at 50 seconds when the leakage was completed, which was the concentration low enough to suffocate the operator.

2) As the asphyxiation accidents due to carbon dioxide has been continuing such as the accident at ○○Electronics in 2018 where the fire extinguishing agent, carbon dioxide, was leaked due to the damage of the selector valve of the fire extinguishing equipment, resulting in 3 casualties, the industrial distribution of carbon dioxide fire extinguishing equipment scattered across business sites, and the status of storage installation, inspection and management were investigated, and the safety measures for carbon dioxide extinguishing equipment suggested as follows.

(1) The number of business sites that have the carbon dioxide fire extinguishing equipment is 282, and the industrial distribution for 630 storages and 2,011 protected areas is as follows. In terms of the region, it was divided into 7 such as the Gyeongnam region, Gyeongbuk region, Seoul metropolitan region, Jeonnam region, Jeonbuk region, Chungnam region and Chungbuk region, and the Seoul metropolitan region has the most storages with 242, followed by the Gyeongnam region and the Chungcheong regions. In terms of the industrial sector, the manufacturing sector has the most storages with 441, followed by the service and other service sectors. Therefore, in terms of the region, intensive management needs to be centered on the Seoul metropolitan and the Gyeongnam regions while the manufacturing sector should be intensively managed in terms of industry.

(2) The number of installation of fire extinguishing agent storage facilities increased 12.7 times from 23 locations before the 1980s to 293 locations in the 1990s. Since the 2000s, the use of carbon dioxide, which accounts for most of the greenhouse gas reduction targets, has been slightly declining due to restrictions in the use of carbon dioxide following the international treaties on global warming. In addition, domestic fire regulations should be improved in line with global standards, where environmental concerns and regulations are being strengthened, and at the same time, new fire extinguishing equipment systems and fire extinguishing agents need to be developed.

(3) A number of accidents involving casualties occur in the carbon dioxide fire extinguishing equipment, which is gas-based fire extinguishing equipment. The toxicity of carbon dioxide itself is low, but it can reduce the oxygen concentration depending on the released carbon dioxide concentration, which leads to a high risk of an asphyxiation accident. Thus, the total number of protected areas responding to the leakage of carbon dioxide from the carbon dioxide fire extinguishing equipment is 2,011, and the average number of protected areas covered by one storage is 3. The number of the storages that cover 1 - 5 protected areas is 558 (89%), accounting for the most of storages, and the maximum number of protected areas covered by a single storage is 28. Therefore, a review to strengthen legal regulations is needed, which enforce the location where carbon dioxide fire extinguishing equipment is installed to be limited to the area where there are no people around, and the protected areas to be installed separately.

(4) In accordance with the 'High Pressure Gas Safety Control Act', carbon dioxide storage containers are managed by setting an inspection period so that those who store high-pressure gas and incombustible gas undergo regular inspections every two years. Accordingly, carbon dioxide fire extinguishing equipment storages are also undergoing regular inspections. Business sites outsourcing the inspection account for 568 (90%) of the total while 53 manufacturing sites (8%) and 2 non-manufacturing sites are conducting self-inspection. Most of the carbon dioxide fire extinguishing equipment storages (582 locations, 92%) have been inspected in the past two years, and thus the inspection cycle is good. However, the possibility of casualties due to the fire extinguishing agent is high, and as the inspection of facilities and containers that considers safety matters related to human casualties is insufficient with the design of fire extinguishing agents mainly focused on suppression of fires in the protected area or protected object even in the fire control, the regulations on the safety management of facilities and the maintenance of installed facilities should be devised.

(5) The location of most of fire extinguishing equipment storages is above the ground with 468 sites (74%). The safety device to minimize the human casualties includes ventilation equipment, and the number of the facilities with ventilation equipment is 461 (73%). Among them, 283 facilities have forced ventilation, which is less than half of the total, and due to the nature of the facilities, the ventilation equipment is installed at the upper position, which limits the release of carbon dioxide. Natural ventilation was found in 178 facilities, which turned out to be one of the ventilation methods not providing effective ventilation in the enclosed protected area, rather increasing the risk of accidents, and not having detailed regulations. The number of storage facilities without ventilation is 166 (27%). Specific standards for ventilation methods should be strictly set, and detailed regulations for installation of forced ventilation as well as natural ventilation be prepared.

(6) The investigation of the status of safety management found 100 (16%) storage sites where workers are directly exposed to the carbon dioxide extinguishing agent at its release, 515 sites (82%) that have not obtained approval for high-pressure gas safety control, 351 sites (56%) without a gas concentration meter and 56 sites (9%) without a firewall, indicating that safety control was partially substandard. When a worker enters a place where there is a carbon dioxide fire extinguishing system or a protected area where gas is released, a gas concentration meter capable of measuring the carbon dioxide or oxygen concentration should be provided, and a respirator that can be used in case of emergency should be ready in a nearby place. When working, in order to prevent the asphyxiation due to carbon dioxide before, during and after work, the carbon dioxide or oxygen concentration should be measured within the protected area and its surroundings, and only then, after ventilation if necessary, a worker should enter the protected area.

(7) In the selector valve installed in the fire extinguishing equipment storage, the screw (screw thread) type is the most common with 430 sites (68%) just as in the business site where the accident has occurred. Besides, the welding type is used in 109 sites (17%) and others in 91 sites (14%). The National Fire Safety Code (NFSC) 106 on carbon dioxide fire extinguishing equipment stipulates that a selector valve should be installed at every protected area or protected object, and each selector valve be marked with the protected area or protected object covered by it. However, as it lacks details such as the fastening method of the selector valve, the regulations such as the installation of safe devices and the method of fastening the selector valve should be established in order to reduce the human casualties caused by the leakage from the carbon dioxide fire extinguishing equipment.

(8) Carbon dioxide fire extinguishing facilities are installed and maintained on the basis of the National Fire Safety Code 106. However, by focusing on the facilities needed to extinguish fire based on the protected area or object, it relatively lacks the regulations on the life safety. Therefore, in order to prevent human casualties, the following countermeasures are needed. First, before commencement of work, by reviewing the work site drawings and conducting on-site inspection with the person in charge of operating fire safety facilities, the types of fire extinguishing equipment, their arrangement plan, types and forms of fire detectors, the risk of operating the carbon dioxide fire extinguishing equipment, operation of alarm devices, location of emergency exits, and safety measures should be checked. Second, when working in a place where a carbon dioxide fire extinguishing system is installed, the automatic and manual changeover switch must be switched to the 'manual' side (with interlocking with the solenoid valve of the control panel stopped) to prevent malfunction, and a locking device is used to prevent unwanted operation in advance. Furthermore, all people in the building are notified of the date, time, location and details of work through in-house broadcasting and bulletin boards, and a supervisor or watcher is deployed at the site to provide safety and health training regarding the harmful effects and danger of carbon dioxide. Third, how to evacuate before carbon dioxide is released within 30 seconds after the alarm system and the detector of carbon dioxide fire extinguishing equipment are activated should be learned in advance along with the evacuation route and assembly points. In addition, before entering the place where carbon dioxide is released, it should be ventilated completely, and if it is necessary to enter the place under the effect of carbon dioxide for the rescue of lives, a respirator must be worn.