Search Results (9)

Hazardous substances such as hydrogen and chlorine are used in semiconductor manufacturing. When these gasses are discharged, they are mixed with outside air and are connected to a treatment facility through a duct inside a gas box. This study investigated an optimal exhaust design to prevent fire explosions and toxic exposure by optimizing the exhaust volume when hazardous substances leak from the gas box of semiconductor manufacturing equipment. In this study, carbon monoxide was used for modeling. A 75 mm duct was used, and the tracer gas was released into the gas box at 15.4 LPM. The concentrations were measured at nine points inside and outside the gas box. According to the test results, in an experiment designed with 0% air intake, the internal leakage concentration was measured to be more than 25% of the LEL (lower explosive limit) for 10 min when leakage occurred due to stagnant flow, and the outside toxicity concentration was also measured to be more than 50% of the TWA (time-weighted average) value. When the air intake ratio was designed to be 100%, there was a point on the outside that exceeded 50% of the TWA, confirming that excessive air intake could also cause gas to leak outside. Finally, when the intake ratio was designed to be 50% in both directions, it was confirmed that the airflow was maintained smoothly, and the hazardous gasses were safely diluted and discharged through the duct. This study was conducted to improve the safety of workers in the field in the event of leakage of flammable and toxic gasses by testing the location and area of the air intake hole in the gas box exhaust port. Through this effort, the aim is to present specific standards for gas box design and to assist in establishing a legal framework or standardized guidelines. Full article

Current regulations mandate the monitoring of respirable coal mine dust (RCMD) mass and crystalline silica in underground coal mines to safeguard miner health. However, other RCMD characteristics, such as particle size and chemical composition, may also influence health outcomes. This study collected RCMD samples from two underground coal mines and performed detailed chemical speciation. Source apportionment was used to estimate RCMD and silica contributions from various sources, including intake air, fire suppression limestone dust, coal dust, diesel engine exhaust, and rock strata. The mine dust mass-based size distributions were comparable to those recorded over a decade ago, with a peak around 10 μm and the majority of the mass in the supermicron size range. The current mine conditions and mining practices do not appear to have significantly increased the generation of smaller particles. Limestone rock dust was prevalent in many locations and, along with coal dust, was the main contributor to RCMD at high-concentration locations. Silica accounted for over 10% of RCMD mass at several active mining locations, primarily from limestone and rock strata dust. Reducing the concentration of limestone dust and its silica content could reduce RCMD and silica levels. Further cleaning of the intake air could also improve the overall mine air quality. Full article

The air–fuel ratio is a crucial parameter in internal combustion engines that affects optimal engine performance, emissions, fuel efficiency, engine durability, power, and efficiency. Positive pressure ventilators (PPVs) create specific operating conditions for drive units, characterized by a reduced ambient pressure compared to standard atmospheric pressure, which is used to control carburetor-based fuel supply systems. The impact of these conditions was investigated for four commonly used PPVs (with internal combustion engines) in fire services across the European Union (EU), using a lambda (λ), carbon dioxide (CO₂), carbon monoxide (CO), and hydrogen carbon (HC) analyser for exhaust gases. All four ventilators were found to operate with lean and very lean mixtures, with their lambda coefficients ranging from 1.6 to 2.2. The conducted tests of the CO₂, CO, and HC concentrations in the exhaust gases of all four fans show dependencies consistent with theoretical analyses of the impact of the fuel–air mixture on emissions. It can be observed that as the amount of burned air decreases, the values of CO and HC decrease, while the concentration of CO₂ increases with the increase in engine load. Such an operation can accelerate engine wear, increase the emission of harmful exhaust gases, and reduce the effective performance of the device. This condition is attributed to an inadequate design process, where drive units are typically designed to operate within atmospheric pressure conditions, as is common for these engines. However, when operating with a PPV, the fan’s rotor induces significant air movement, leading to a reduction in ambient pressure on the intake side where the engine is located, thereby disrupting its proper operation. Full article

Polyamide-imide (PAI) is an exceptional polymer known for its outstanding mechanical, chemical, and thermal resistance. This makes it an ideal choice for applications that require excellent durability, such as those in the aerospace sector, bearings, gears, and the oil and gas industry. The current study explores the optimization of TORLON^® 4000 T HV polyamide-imide nanofibers utilizing needleless electrospinning devices, ranging from laboratory-scale to industrial-scale production, for the first time. The PAI polymer has been dispersed in several solvent systems at varying concentrations. The diameter of the electrospun PAI nanofibers ranged from 65.8 nanometers to 1.52 μm. Their filtering efficiency was above 90% for particles with a size of 0.3 microns. The TGA results proved that PAI nanofibers have excellent resistance to high temperatures up to 450 °C. The PAI nanofibers are ideal for hot air intake filtration and fire-fighter personal protection equipment applications. Full article

Highly flammable substances such as hydrogen and silane are used in the semiconductor manufacturing process. When gas leaks, it is mixed with outside air and connected to a treatment facility through the duct inside the gas box. This study investigated optimal exhaust design to prevent fire explosions and health problems by optimizing the exhaust volume when hydrogen leaks from the gas box of semiconductor manufacturing equipment. After selecting the leakage rate amount based on the KS C IEC 60079-10-1, SEMI S6-0707E, and SEMI F-15 standards, a gas box was manufactured. Subsequently, the fan speed required to ventilate the gas box more than five times per minute according to the SEMI standard and the opening area and location that can reduce the lower explosive limit (LEL) to less than 25% in the event of hydrogen leakage were determined. When the air intakes were placed on the left and right, the flow rate was measured at 32 L per minute (LPM), and the maximum concentration was measured at 9111 ppm. This is less than 25% of the LEL of hydrogen and is believed to be capable of preventing fire and explosion, even if a similarly flammable gas leaks inside the gas box. Full article

In this study, the operating processes of a four-stroke diesel marine engine from the intake valve closing (IVC) to the exhaust valve opening (EVO) at numerous different charge air conditions were simulated with the AVL FIRE code. The CFD models were validated with engine shop-test technical data. The results showed that increasing the charge air pressure without cooling decreased the actual amount of air supplied to the cylinder. As a result, the combustion process was suboptimal, resulting in a reduction in engine power and an increase in specific fuel oil consumption (SFOC). In addition, less air to cool the combustion chamber coupled with elevated charge air temperatures increased the in-cylinder peak temperature, leading to a significant increase in thermal nitric oxide (NO) emissions. In contrast, by cooling the charge air after turbocharging, the actual amount of air entering the engine cylinders was increased. The abundant charge air helped to cool the combustion chamber better, significantly reducing the in-cylinder peak temperature and then the thermal NO formation. Better combustion also increased engine power, which, in turn, reduced SFOC. In addition, carbon dioxide (CO₂) and soot emissions were also reduced. Full article

Air-doors are important facilities for regulating the air flow in a mine ventilation network. It is of value to study the influence of air-doors, which are adjacent to a fire source on smoke back-layering in order to build a rational ventilation system. By regulating air-doors in a mine ventilation network test platform, two typical mine ventilation networks, with parallel branches and a diagonal branch, were constructed. During the study, into the closing degree of the air-doors adjacent to a fire source in a ventilation network with parallel branches, the back-layering length is up to 3.70 m when the ventilation velocity is 1.40 m/s. When the air-door on the return side of the adjacent branch is closed, the back-layering subsides within 1 min and the upstream temperature drops rapidly to normal. When the air-door is half closed, there is still a back-layering flow within 5 min. Smoke control, with the air-door is closed, is better than when the air-door is half closed. Based on this, tests into the influence of the closing position of air-doors, which are adjacent to a fire source, were carried out in a ventilation network with a diagonal branch. Results indicate that when the ventilation velocity is 1.70 m/s, the back-layering flow spreads to the diagonal branch, and the air flow velocity of both the adjacent branch and the diagonal branch increases. When closing the air-door on the return side of the adjacent branch, the back-layering rapidly subsided. The wind velocity on the intake side of the adjacent branch is stabilized after a rapid decrease, and the wind velocity of the diagonal branch is stabilized after a rapid increase. When closing the air-door on the intake side of the adjacent branch, the smoke from the diagonal branch spreads. Compared with closing the intake side air-door, closing the air-door on the return side of the adjacent branch is more effective in preventing back-layering. This work provides a reference for preventing back-layering and guiding the evacuation of people from the upstream of a fire source. Full article

In September 2020, a fire at a liquefied natural gas (LNG) plant in the Arctic areas of Norway received national attention. In an unengaged air intake, the heat exchanger designed to prevent ice damage during production mode, was supplied hot oil at 260 °C. In sunny weather, calm conditions, and 14 °C ambient temperature, overheating of the unengaged air intake filters (85% glass fiber and 15% polyester) was identified as a possible cause of ignition. Laboratory heating tests showed that the filter materials could, due to the rigid glass fibers carrying the polymers, glow like smoldering materials. Thus, self-heating as observed for cellulose-based materials was a possible ignition mechanism. Small-scale testing (10 cm × 10 cm and 8 cm stacked height) revealed that used filters with collected biomass, i.e., mainly pterygota, tended to self-heat at 20 °C lower temperatures than virgin filters. Used filter cassettes (60 cm by 60 cm and 50 cm bag depth) caused significant self-heating at 150 °C. At 160 °C, the self-heating took several hours before increased smoke production and sudden transition to flaming combustion. Since the engaged heat exchanger on a calm sunny day of ambient temperature 14 °C would result in temperatures in excess of 160 °C in an unengaged air intake, self-heating and transition to flaming combustion was identified as the most likely cause of the fire. Flames from the burning polymer filters resulted in heat exchanger collapse and subsequent hot oil release, significantly increasing the intensity and duration of the fire. Due to firewater damages, the plant was out of operation for more than 1.5 years. Better sharing of lessons learned may help prevent similar incidents in the future. Full article

This paper presents a method for determining the sensitivity of the main air flow directions in ventilation subnetworks to changes in aerodynamic resistance and air density in mine workings. The authors have developed formulae for determining the sensitivity of the main subnetwork air flows by establishing the degree of dependency of the air volume stream in a given working on the variations in resistance or air density of other workings of the network. They have been implemented in the Ventgraph mine ventilation network simulator. This software, widely used in Polish collieries, provides an extended possibility to predict the process of ventilation, air distribution and, in the case of underground fire, the spread of combustion gasses. The new method facilitates an assessment by mine ventilation services of the stability of ventilation systems in exploitation areas and determines the sensitivity of the main subnetwork air flow directions to changes in aerodynamic resistance and air density. Recently in some Polish collieries new longwalls are developed in seams located deeper than the bottom of the intake shaft. Such a solution is called “exploitation below the level of access” or “sublevel”. The new approach may be applied to such developments to assess the potential of changes in direction and air flow rates. In addition, an interpretation of the developed sensitivity indicator is presented. While analyzing air distributions for sublevel exploitation, the application of current numerical models for calculations of the distribution results in tangible benefits, such as the evaluation of the safety or risk levels for such exploitation. Application of the Ventgraph computer program, and particularly the module POŻAR (fire) with the newly developed options, allows for an additional approach to the sensitivity indicator in evaluating air flow safety levels for the risks present during exploitation below the level of the intake shaft. The analyses performed and examples presented enabled useful conclusions for mining practice to be drawn. Full article