• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.1
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• pp.43-49
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• 2008

This study is about an influence of harmful factors of welding fumes such as Fe, Mn, Cu, Zn to workers who inhales them in welding sites. The influence can be measured with the density of heavy metals in blood after welding. The main factors of the measurement are TWA, a density of welding fume, and a level of heavy metals. The results indicate that there is a positive effect of moving fans as a way of improving the condition in welding workplaces. While welding was done, TWA exceeded the level of Fe 40% and Zn 10% and the level of heavy metals in blood was below the standard for the workers who were under the experiment. Also when the wind was applied on the front side by a fan, the welding fume significantly reduced. It can be concluded that wearing protection gears with safety devices is one of important factors.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.9 no.1
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• pp.87-98
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• 1999

The objectives of this study were to evaluate exposures to airborne methylene chloride and postshift carboxyhemoglobin (COHb) in blood of workers engaged in processes using blowing or cleaning agents, and to investigate correlation between methylene chloride concentrations and the blood COHb levels of workers. The geometric mean (GM) of workers' exposures (8 hour-time weighted averages, TWA) to airborne methylene chloride during cleaning molds using rags wetted with the solvent in the manufacture of flexible polyurethane foam (GM = 61.4 ppm), during operating the dip tank for cleaning molds in the manufacture of lens (GM = 61.0 ppm), and during cleaning the blowing nozzles by spraying the solvent in the manufacture of shoes (GM = 117.2 ppm) were exceeded the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value ($TLV^{(R)}$)-Time Weighted Average (TWA) (50 ppm). The COHb levels were significantly different among groups (p<0.05). The average COHh levels in blood of non-smoking workers were 2.0% in. low-level (<50 ppm) exposure group, and 3.9 % in high-level (>50ppm) exposure group. The average COHb levels in smoking workers were 3.1% in low-level exposure group, and 4.8% in high-level exposure group. The blood COHb levels of no-exposed workers to methylene chloride were 1.8% in non-smoking group, and 2.8% in smoking group. It was found that the COHb level dependeds on the methylene chloride concentration and smoking habit, and was highly correlated with methylene chloride concentration in air. The correlation coefficient was 0.81 among non-smoking workers. The estimated COHb level (3.6%) and 95% upper confidence limit (4.0%) corresponding to TLV-TWA of methylene chloride exceeded the current ACGIH Biological Exposure Index (COHb 3.5%) for carbon monoxide. The estimated COHb level (5.4%) at 100 ppm exceeded the standard (5%) recommended by National Institute for Occupational Safety and Health (NIOSH) for preventing adverse cardiovascular effect. The estimated COHb value and 95% upper confidence limit at 25 ppm of the Occupational Safety and Health. Adminstration (OSHA) Permissible Exposure Limit-TWA (PEL-TWA) were 2.6% and 3.0%, respectively. It is suggested that COHb in blood be kept below 3.0% to comply with OSHA PEL-TWA.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.25 no.2
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• pp.134-145
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• 2015

Objectives: An objective of this study was to perform a risk assessment and social cost-benefit analysis for revising permissible exposure limits for seven substances: Nickel(Insoluble inorganic compounds), benzene, carbon disulfide, formaldehyde, cadmium(as compounds), trichloroethylene, touluene-2,4-diisocyanate. Materials and Methods: The research methods were divided into risk and hazard assessment and cost-benefit analysis. The risk and hazard assessment for the seven substances consists of four steps: An overview of GHS MSDS(1st), review of document of ACGIH's TLVs (2nd), comparison between international occupational exposure limits and domestic permissible exposure limits(3rd), and analysis of excess workplace and excess rate for occupational exposure limits based on previous work environment measurement data(4th). Total cost was estimated using cost of local exhaust ventilation, number of excess workplace and penalties for exceeding a permissible exposure limit. On the other hand, total benefit was calculated using the reduction rate of occupational disease, number of workplaces treating each substance and industrial accident compensation. Finally, the net benefit was calculated by subtracting total cost from total benefit. Results: All the substances investigated in this study were classified by CMR(Carcinogens, Mutagens or Reproductive toxicants) and their international occupational exposure limits were stricter than the domestic permissible exposure limits. As a result of excess rate analysis, trichloroethylene was the highest at 11%, whereas nickel was the lowest at 0.5%. The excess rates of all substances except for trichloroethylene were observed at less than 10%. Among the seven substances, the total cost was highest for trichloroethylene and lowest for carbon disulfide. The benefits for the seven substances were higher than costs estimated based on strengthening current permissible exposure limits. Thus, revising the permissible exposure limits of the seven substances was determined to be acceptable from a social perspective. Conclusions: The final revised permissible exposure limits suggested for the seven substances are as follows: $0.2mg/m^3$ for nickel, 0.5 ppm(TWA) and 2.5 ppm(STEL) for benzene, 1 ppm(TWA) for carbon disulfide, $0.01mg/m^3$(TWA) for cadmium, 10 ppm(TWA) and 25 ppm(STEL) for trichloroethylene, 0.3 ppm(TWA) for formaldehyde, and 0.005 ppm(TWA) and 0.02 ppm(STEL) for toluene diisocynate(isomers).

• 월간산업보건
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• s.308
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• pp.52-54
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• 2013

Phenyl glycidyl ether의 직업적 노출기준 TLV-TWA는 0.1 ppm($0.6mg/m^3$)으로 권고되고 있다. TLV-TWA는 동물실험에서 고환(정소) 독성, 비암 그리고 감작반응에 대한 위험도를 줄일 수 있다고 증명된 수준이다. 또한 사람에서의 감작반응이 보고되고 흰쥐에서 비암이 입증되어 경고표시(notation)로 SEN과 A3(동물에서 발암성 물질)를 권고하였다. Phenyl glycidyl ether와 다른 glycidyl ether에 노출된 근로자들에서 평균 6.5개월 후에 감작반응이 발견되어, 교차 감작반응의 가능성을 인지하여야 한다. Phenyl glycidyl ether를 흰쥐와 토끼에게 급성으로 피부에 도포한 결과 빠르게 흡수되어 조혈독성이 유발되는 것을 확인하여 피부(Skin) 경고표시의 타당성을 입증하였다.

• 월간산업보건
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• s.371
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• pp.28-31
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• 2019

피부, 눈 및 상부 호흡기의 자극 가능성을 최소화하기 위해, 인산(Phosphoric acid)에 대한 직업적 노출기준 TLV-TWA를 $1mg/m^3$, 그리고 TLV-STEL을 $3mg/m^3$으로 권고하였다. 수분이 있는 상태에서 인산 먼지나 인산 케이크에 의한 피부 접촉은 특히 자극적이다. TLV-TWA의 권고수준은 산에 노출 경험이 없는 노동자들에게 인후염을 일으키는 인산의 공기 중 농도보다 낮은 수준이다. 또한 인산 노출에 순응된 노동자들에게 유발할 수 있는 농도보다는 훨씬 더 낮은 수준이다. 피부(Skin), 감작성(SEN) 또는 발암성 경고표지(Notation)를 권고하기에는 충분한 자료가 없다.

• Journal of the Korean Chemical Society
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• v.45 no.2
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• pp.177-182
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• 2001

An instructional model using multiple analogies according to component process (MACP) was designed on the vasis of schema theory and comornent process theory in analogical reasoning. This model has ？ phases: introducting multiple analsgs, extracting multiple analogs, extracting common attributes of analogs, introducing target conanother context. Te instructional effects of this model upon students' conceptual understanding and learning motivation were compared with those of the Teaching-With-Analogy (TWA) and non-analogy instructions. Three classes of 8th grade were randomly assigned to MACP, TWA, and control group, respectively, Subjects were taught about chemical changes and reactions for 10 class hours. The ANCOVA results indicated that the scores of the conceptions test for the MACP group were significantly higher than for the control graup. However, no significant differences were found among the three groups in the test scores of learning motivation.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.6_spc
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• pp.729-735
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• 2016

According to the survey for working environment of the cashiers in highway tollbooths, workers replied that noise was the most harmful substances next to air pollutant in the tollbooth. Researches on the noise levels exposed to cashiers in the highway tollbooth scarcely have been performed. Therefore, the aim of this study was to acquire baseline data to prevent health impairments of the cashiers by evaluating noise level exposed to them. Noise dosimeters were used for monitoring workers' noise exposure level in the tollbooths at 8 different highway tollgates. The noise levels of tollbooths did not exceed noise exposure limit of the ministry of labor, 90 dB(A). The average TWA inside of the tollbooths was 55.4 dB(A) and the average TWA outside of tollbooths was 58.3 dB(A). The average TWA outside of tollbooths was slightly higher than that of inside of tollbooths. However, the significance probability(p-value) was 0.255 which means statistically not significant. The noise levels inside and outside of tollbooth were statistically significant to both mean traffic volume per day and traffic volume of passenger car.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.31 no.3
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• pp.255-265
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• 2021

Objectives: The purpose of this study is to analyze the exposure characteristics of inorganic acids. Methods: We analyzed exposure data (n = 363,146) for six inorganic acids (hydrogen fluoride, hydrogen bromide, hydrogen chloride, phosphoric acid, nitric acid, and sulfuric acid) collected between 2017 and 2019 in South Korea. Measurement characteristics and exposure levels (ELs) were analyzed by inorganic acid, industry category, enterprise size, and measurement year. Results: Measurement percentage dominated in time-weighted average (TWA, 91%) compared to short term exposure limit (STEL) and Ceiling. Most of the measurements (79.7%) were collected from the manufacturing category of industry. Medians of ELs were mostly low (≤3% of the threshold limit), with the exception of sulfuric acid (4.6% of TWA and 10.5% of STEL). The percentages of exceeding 1% of the occupational exposure limits (OELs) in TWA were relatively high for sulfuric acid (35.8%) and hydrogen chloride (16.5%) compared to the other acids (4.2%-6.6%). In addition, the percentages of exceeding 1% of OELs in STEL or Ceiling were higher for sulfuric acid (22.9%), hydrogen chloride (12.3%), and nitric acid (8.2%) compared to the other acids (1.2%-1.9%). The small-sized enterprises showed higher ELs in TWA; contrarily, the large-sized enterprises had higher ELs in STEL or Ceiling. Conclusions: The measurement characteristics and ELs identified in this study could be useful for establishing safety and health policies for inorganic acids.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.5
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• pp.827-834
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• 2022

Recently, marine surveys using unmanned ships are attracting attention, and research on small unmanned ships using sails is on the rise. Sail drones can be used for marine surveys, monitoring, and pollution management. Therefore, in this study, using the method of estimating the ship speed for twin sail drones, the optimal conditions for sailing are checked, and the performance to be considered in the initial design stage, such as the motion performance and resistance of the sail drone. Consequently, the twin sail drone had a speed lower than 2.0 m/s, and the stability satisfied the rule by DNV. In addition, the maximum speed at an angle of attack of 20° at TWA 100° was 1.69 m/s and that at an angle of attack of 25° at TWA 100° was 1.74 m/s.

• Journal of The Korean Association For Science Education
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• v.27 no.9
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• pp.778-786
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• 2007

This study investigated the effects of analyzing mapping errors on conceptual understanding, mapping understanding and perceptions of the instructions in learning chemistry concept with analogy. Seventh graders (N=121) at two middle schools were assigned to the comparison and the treatment groups, and were taught about 'states of matter and arrangement of molecules.' The students in the comparison group were taught in the Teaching-With-Analogy (TWA) model, while those in the treatment group Were taught in the instructional model that changed 'mapping similarity' and 'indicating difference' of the TWA model into 'analyzing mapping errors.' Analysis of the results revealed that the scores of the conception test and the mapping test for the treatment group were significantly higher than those far the comparison group regardless of field dependence-independence. It was also found that most students in the two groups positively perceived the instructions with analogy, but the students in the treatment group had difficulties in analyzing mapping errors, Educational implications are discussed.