National Institute of Occupation Safety and Health

Tokyo, Japan

National Institute of Occupation Safety and Health

Tokyo, Japan
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Choi K.S.,National Institute of Occupation Safety and Health | Mogami T.,Kasuga Denki Inc. | Suzuki T.,Kasuga Denki Inc. | Kim S.C.,Chungbuk National University | Yamaguma M.,National Institute of Occupation Safety and Health
Journal of Loss Prevention in the Process Industries | Year: 2013

As a method to prevent or mitigate electrostatic charge and/or discharges, we have developed a novel AC electrostatic ionizer. In this study, we evaluated experimentally the practical version of the novel AC electrostatic ionizer with a modeling test system and a pneumatic powder transport facility. In addition, electrostatic discharges generated inside a silo while loading polypropylene (PP, 3 mm) granules were observed visually with/without the novel AC ionizer. The specific charge was clearly decreased with the novel AC electrostatic ionizer. The specific charge obtained with the four arranged AC electrostatic ionizers used was approximately one eighth of that without the AC ionizer. The incendiary bulk surface discharges completely died out inside the silo by using the four arranged ionizers. © 2012 Elsevier Ltd.


Choi K.,National Institute of Occupation Safety and Health | Mogami T.,Kasuga Denki Inc. | Suzuki T.,Kasuga Denki Inc.
Review of Scientific Instruments | Year: 2014

To detect electrostatic discharges generated by polymer granules within a metal silo, we developed a novel and simple electrostatic discharge detector that utilizes a photosensor. The novel detector consists of a photosensor module in a metal cylinder, an optical band-pass filter, a quartz glass, a power supply, an amplifier for the photosensor module, and a digital oscilloscope. In this study, we conducted experiments at a real pneumatic powder transport facility that includes a metal silo to evaluate the novel detector using polypropylene granules. To determine the performance of the novel detector, we observed the electrostatic discharge within the metal silo using a conventional image intensifier system. The results obtained from the experiments show that the novel detector worked well in this study. The signals obtained with the novel detector were identical to the electrostatic discharges obtained with the conventional image intensifier system. The greatest advantage of this novel detector is that it is effective even when placed under external lights. In addition, the influence of various optical band-pass filters on the performance of the novel detector was discussed. Our study confirmed that an optical band-pass filter with a center wavelength of λ 330 nm (λ 1/2: 315-345 nm) was the best performer among the optical band-pass filters used in this study. © 2014 AIP Publishing LLC.


Pyrgiotakis G.,Boston University | Vedantam P.,Boston University | Cirenza C.,Boston University | McDevitt J.,Boston University | And 3 more authors.
Scientific Reports | Year: 2016

A chemical free, nanotechnology-based, antimicrobial platform using Engineered Water Nanostructures (EWNS) was recently developed. EWNS have high surface charge, are loaded with reactive oxygen species (ROS), and can interact-with, and inactivate an array of microorganisms, including foodborne pathogens. Here, it was demonstrated that their properties during synthesis can be fine tuned and optimized to further enhance their antimicrobial potential. A lab based EWNS platform was developed to enable fine-tuning of EWNS properties by modifying synthesis parameters. Characterization of EWNS properties (charge, size and ROS content) was performed using state-of-the art analytical methods. Further their microbial inactivation potential was evaluated with food related microorganisms such as Escherichia coli, Salmonella enterica, Listeria innocua, Mycobacterium parafortuitum, and Saccharomyces cerevisiae inoculated onto the surface of organic grape tomatoes. The results presented here indicate that EWNS properties can be fine-tuned during synthesis resulting in a multifold increase of the inactivation efficacy. More specifically, the surface charge quadrupled and the ROS content increased. Microbial removal rates were microorganism dependent and ranged between 1.0 to 3.8 logs after 45 mins of exposure to an EWNS aerosol dose of 40,000 #/cm3. © 2016, Nature Publishing Group. All rights reserved.


Choi K.,National Institute of Occupation Safety and Health | Mogami T.,Kasuga Denki Inc. | Suzuki T.,Kasuga Denki Inc. | Yamaguma M.,National Institute of Occupation Safety and Health
Global Congress on Process Safety 2014 - Topical Conference at the 2014 AIChE Spring Meeting and 10th Global Congress on Process Safety | Year: 2014

This paper is a report on the relationship between the charge amount (charge to mass ratio) of polypropylene (PP) granules and the electrostatic discharges that occur while loading a metal silo. The feedback control system was used in order to control the charge to mass ratio of PP granules. The electrostatic discharges inside the silo were also observed using a conventional image-intensifier system. The results obtained from the experiments show that (1) two kinds of electrostatic discharges were clearly observed inside a metal silo while loading PP granules, i.e., brush discharges and incendiary bulk surface discharges; (2) the number of brush discharges and incendiary bulk surface discharges increased with the increase in the charge to mass ratio of PP granules, almost reaching saturation; and (3) brush discharges and incendiary bulk surface discharges began to occur at the -1.16 μC/kg and -2.33 μC/kg points in the charge to mass ratio, respectively, in this study.


Choi K.,National Institute of Occupation Safety and Health | Sakurai N.,Asahi Sunac Corporation | Yanagida K.,Asahi Sunac Corporation | Itoh H.,Asahi Sunac Corporation
Journal of Loss Prevention in the Process Industries | Year: 2010

Electrostatic Powder coating which is a surface finishing technique has widely been used in paint industry since its invention in the 1960s. However, so far, insufficient attention has been paid to the powder fires and/or explosion hazards caused by electrostatic spark during coating process. This paper is a report of the electrostatic spark ignitability of aluminous coating powders (dry blend-type) used in practical electrostatic powder coating. The Hartman vertical-tube apparatus was used for the minimum ignition energy (MIE) test. Various aluminous coating powders, different with respect to the amount of aluminum pigment, were used in this study. Experimental results obtained in this study are as follows: (1) The aluminous coating powder was so sensitive that even an electrostatic spark with an energy as low as 10 mJ could ignite it. (2) The particle size of aluminous coating powder has a considerable effect on the ignitability when the aluminum pigment concentration is within 6 wt% of the practical coating powder manufacturing standards. Thus, the conventional expression for estimating the MIE can be useful when assessing the electrostatic hazards associated with aluminum coating powders. © 2009 Elsevier Ltd. All rights reserved.


Mogami T.,Ibaraki University | Suzuki T.,Kasuga Denki Inc. | Choi K.S.,National Institute of Occupation Safety and Health | Ikehata T.,Ibaraki University
Journal of Loss Prevention in the Process Industries | Year: 2010

As a method to prevent or mitigate cone discharges in a specific section such as a large silo, we have developed a new feedback control-type ionizer system. The feedback control-type system is composed mainly of an ionizer, an electrostatic field strength meter, and computer control equipment. In this study, we evaluated experimentally the practical version of the feedback control-type ionizer system through several tests in a pneumatic powder transport facility. The specific charges of the falling pellets in the silo were also measured for 10 s using a Faraday cage. Polypropylene (PP) pellets with a mean particle size of 3 mm were used in this experiment. The results of the experiment revealed that the feedback control-type ionizer system had the following characteristics: (1) it is possible to control the performance of the ionizer with a supply current; (2) the electrostatic field strength in the loading pipe from the charged powder is reduced and maintained at near zero by using the feedback control-type system; and (3) the performance of the feedback control-type system is superior to that of others, such as the conventional AC- or DC-type ionizers. © 2009 Elsevier Ltd. All rights reserved.


Choi K.,National Institute of Occupation Safety and Health | Mogami T.,Kasuga Denki Inc. | Suzuki T.,Kasuga Denki Inc. | Yamaguma M.,National Institute of Occupation Safety and Health
Journal of Loss Prevention in the Process Industries | Year: 2016

As a method of preventing or mitigating explosion due to electrostatic discharges during the loading of polymer granules in a metal silo, we have developed a novel bipolar electrostatic ionizer. In this study, we investigated experimentally a practical version of the bipolar electrostatic ionizer with a modeling test device to measure the charge-neutralizing current, and a full-sized pneumatic powder transport facility. The electrostatic discharges generated inside a silo while loading polypropylene (PP) granules were also observed visually with/without the novel bipolar electrostatic ionizer. As a sample, 300 kg of polypropylene granules 2-3 mm in size was used in this study. The specific charge of the polypropylene granules was clearly decreased by approximately 85 percent with the novel bipolar electrostatic ionizer. The brush discharges, as well as the incendiary bulk surface discharges, completely died out inside the silo when the novel bipolar electrostatic ionizer used. © 2016 Elsevier Ltd.


Choi K.,National Institute of Occupation Safety and Health | Mogami T.,Kasuga Denki Inc. | Suzuki T.,Kasuga Denki Inc. | Yamaguma M.,National Institute of Occupation Safety and Health
Journal of Loss Prevention in the Process Industries | Year: 2014

This paper is a report on the relationship between the charge amount (charge to mass ratio, q/. m) of polypropylene (PP, 2-3mm) granules and the frequency of electrostatic discharges that occur while loading a metal silo. The feedback control system was used in order to control the q/. m of PP granules. The electrostatic discharges inside the silo were also observed using a conventional image-intensifier system. The charging control range for PP granules was from 0 to-12μC/kg in the q/. m. The results obtained from the experiments show that (1) two kinds of electrostatic discharges were clearly observed inside a metal silo while loading PP granules, i.e., brush discharges and incendiary bulk surface discharges; (2) the number of brush discharges and incendiary bulk surface discharges increased with the increase in the q/. m of PP granules, almost reaching saturation; and (3) brush discharges and incendiary bulk surface discharges began to occur at the-1.16μC/kg and-2.33μC/kg points in the q/. m, respectively, in this study. © 2014 Elsevier Ltd.


Choi K.,National Institute of Occupation Safety and Health | Kim S.,Chungbuk National University | Chung J.,Seoul National University of Science and Technology
Advanced Science Letters | Year: 2013

This paper reports on electrostatic hazards related to the freeboard region of a powder fluidized bed reactor. The electrostatic field strength E (kV/cm) was monitored over the fluidizing time. A powder fluidized bed system and four kinds of sample powders-polyvinyl chloride (PVC), methyl methacrylate butadiene styrene (MBS), polyamide11 (PA11), and cellulose (CL)) were used in the experiments. The superficial air velocity, Ug, with zero relative humidity, was mainly 0.53 m/s to facilitate stable fluidization. Results obtained from the experiments show that MBS, PA11, and CL (except PVC) have large E values, far from safe in electrostatic hazards, during operation. The E in the freeboard region was significantly affected by powder adhering to the inner wall, as well as by the amount of suspended fine powders. CL of the poor flowability showed the highest potential of electrostatic hazards among the sample powders used in this paper. © 2013 American Scientific Publishers All rights reserved.


PubMed | Boston University, National Institute of Occupation Safety and Health and European University Cyprus
Type: | Journal: Scientific reports | Year: 2016

A chemical free, nanotechnology-based, antimicrobial platform using Engineered Water Nanostructures (EWNS) was recently developed. EWNS have high surface charge, are loaded with reactive oxygen species (ROS), and can interact-with, and inactivate an array of microorganisms, including foodborne pathogens. Here, it was demonstrated that their properties during synthesis can be fine tuned and optimized to further enhance their antimicrobial potential. A lab based EWNS platform was developed to enable fine-tuning of EWNS properties by modifying synthesis parameters. Characterization of EWNS properties (charge, size and ROS content) was performed using state-of-the art analytical methods. Further their microbial inactivation potential was evaluated with food related microorganisms such as Escherichia coli, Salmonella enterica, Listeria innocua, Mycobacterium parafortuitum, and Saccharomyces cerevisiae inoculated onto the surface of organic grape tomatoes. The results presented here indicate that EWNS properties can be fine-tuned during synthesis resulting in a multifold increase of the inactivation efficacy. More specifically, the surface charge quadrupled and the ROS content increased. Microbial removal rates were microorganism dependent and ranged between 1.0 to 3.8 logs after 45 mins of exposure to an EWNS aerosol dose of 40,000 #/cm(3).

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