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An Engineer’s View of Human Error
Published in Philip D. Bust, Contemporary Ergonomics 2006, 2020
Do not assume that chemical engineers would not make similar errors. In 1989, in a polyethylene plant in Texas, a leak of ethylene exploded, killing 23 people. The leak occurred because a vessel was opened for repair while the air-operated valve isolating it from the rest of the plant was open. It was open because the two compressed air hoses, one to open the valve and one to close it, had been disconnected and then replaced wrongly. The accident, some might say, was due to an error by the person who re-connected the hoses. This is an error waiting to happen, a trap for the operator, a trap easily avoided by using different types or sizes of coupling for the two connections. This would have cost no more than the error-prone design (Figure 3) (Anon., 1990).
Concrete Technology in the Century of the Environment
Published in K. Sakai, Integrated Design and Environmental Issues in Concrete Technology, 2014
A form, 15m in length and with transparent sides as shown in Fig.7, was filled with water and the antiwashout underwater concrete was placed from the side to a depth of 1.5m using a tremie. The tip of the tremie was equipped with a compressed-air operated valve, by opening and closing which the placing speed was adjusted. The placing speed, V, of the concrete was made V=0.1m/h and V=0.4m/h to reflect actual construction data. After every one tenth of the total volume had been placed, the flow gradient of the concrete was measured.
Accidents caused by simple slips
Published in Trevor Kletz, An engineer’s view of human error, 2018
Do not assume that chemical engineers would not make similar errors. In 1989, in a polyethylene plant in Texas, a leak of ethylene exploded, killing 23 people. The leak occurred because a line was opened for repair while the air-operated valve isolating it from the rest of the plant was open. It was open because the two compressed air lines, one to open the valve and one to close it, had identical couplings, and they had been interchanged. As well as this slip there was also a violation, a decision (authorized at a senior level) not to follow the normal company rules and industry practice which required a blind flange or double isolation valve (Figure 2.14)29 (see also Section 5.2.5, page 105).
Production and characterization of ultrafine aspirin particles by rapid expansion of supercritical solution with solid co-solvent (RESS-SC): expansion parameters effects
Published in Particulate Science and Technology, 2020
Hossein Rostamian, Mohammad Nader Lotfollahi
The schematic diagram of experimental RESS-SC apparatus is shown in Figure 2. This apparatus was used for production of aspirin particles. In the present study, two separate units including extraction and expansion units were utilized to conduct RESS-SC experiments. A supercritical fluid extraction system (SITEC-Sieber Engineering Switzerland) (Baseri, Asl, and Lotfollahi 2010; Baseri, Lotfollahi, and Asl 2011) was used as an extraction unit. In this unit, carbon dioxide was liquefied by a refrigeration process. Subsequently, a metering pump (1.5kW, LEWA) and a pressure control valve (air operated valve) were used to compress carbon dioxide. The temperature of the extraction cell was controlled by a thermostatic bath up to 80 °C (with a readability of ±0.2 °C). The extraction column was packed by the pulverized glass with a mean particle size of 0.55cm and a mixture of 20g of aspirin and 15g of menthol. The role of glass particles was to increase the contact surface and to decrease the time required to achieve equilibrium. After adjusting the operating pressure and temperature for the extraction vessel, the supercritical solution was kept in the extraction vessel for about 8.5h to attain equilibrium. The equilibrium time was obtained by performing various experiments. Then, the supercritical solution was passed through the pre-expansion line (a high-pressure heated tube) and it was suddenly expanded through a nozzle. In this study, two kinds of nozzles – capillary and orifice – with various sizes and shapes were utilized. Temperature of the pre-expansion part was controlled by an electric heater up to 120 °C (with an accuracy of ±1 °C). The expansion unit (Baseri and Lotfollahi 2014) had a needle valve, a pre-expansion line, and an expansion chamber. The expansion vessel had a total capacity of 2000cm3. It was a steel cylindrical vessel (8cm ID and 40cm length), which was able to control the operating pressure and temperature. A back pressure regulator was used to control the pressure of expansion vessel (up to 16±1bar). In addition, a hot water jacket was applied to control the expansion vessel’s temperature. The particles produced in the expansion vessel were collected by a glass plate at a specific distance from the discharge of the nozzle (known as the spray distance). The spray distance could be in the range of 0.5–20 cm (with a readability of ±0.1cm). Menthol in final samples must be completely removed prior to any samples analysis. Therefore, all samples were maintained about 1 week at ambient temperature and pressure. In addition, all samples were kept under a vacuum pressure of 5 mbar for 4h to ensure the complete removal of menthol from the samples. No more weight reduction was observed when more vacuum was implemented for removing of menthol.