Field‑based Heatwave Risk Assessment of Outdoor Workers Measured by Wearable Sensors

김아라,유가영 한국기상학회 2023 Asia-Pacific Journal of Atmospheric Sciences Vol.59 No.4

Increasing heatwave frequency due to climate change threatens outdoor workers’ health. We aimed to assess the on-siteheat strain level of outdoor workers using wearable sensors and identify the factors for consideration in developing individual-based heat adaptation strategies. Seven road construction workers were recruited and asked to wear necklace-formtemperature loggers and smartwatches monitoring heart rate (HR). The questionnaire was delivered daily to ask about theirpsychological comfort level during work. Workers were exposed to up to 5.4 °C higher temperature than the official airtemperature, indicating that the national heatwave alarm does not reflect on-site heat conditions. Based on the measured HRdata, heat strain levels were defined. When HR exceeded the level of “180-age,” we assumed extreme heat strain occurred,which requires immediate cessation of work. When HR exceeded 40% of the individual heart rate reserve (the differencebetween the maximum and resting HR), we assumed high heat strain occurred, indicating a stressed condition. High heatstrain occurred in all workers on 9 of the 13 monitored days, whereas the official heatwave alarms were issued only on fourdates. Additionally, three workers experienced extreme heat strain on two dates. The main factor for workers experiencingextreme heat strain was age. Comparing the heat strain levels from HR with the survey results, we found that the olderworkers considered their condition comfortable even under extreme and high heat strain. Thus, an individual sensor-basedearly-warning system is needed to prevent heat strain not perceived by outdoor workers. The findings emphasize the need fora personalized adaptation strategy for heatwaves and will be a baseline for developing a new work manual that mainstreamsclimate change impacts.

An interpretable machine learning approach for forecasting personal heat strain considering the cumulative effect of heat exposure

서승원,최유진,구충완 한국건설관리학회 2023 한국건설관리학회 논문집 Vol.24 No.6

Climate change has resulted in increased frequency and intensity of heat waves, which poses a significant threat to the health and safety of construction workers, particularly those engaged in labor-intensive and heat-stress vulnerable working environments. To address this challenge, this study aimed to propose an interpretable machine learning approach for forecasting personal heat strain by considering the cumulative effect of heat exposure as a situational variable, which has not been taken into account in the existing approach. As a result, the proposed model, which incorporated the cumulative working time along with environmental and personal variables, was found to have superior forecast performance and explanatory power. Specifically, the proposed Multi-Layer Perceptron (MLP) model achieved a Mean Absolute Error (MAE) of 0.034 (℃) and an R-squared of 99.3% (0.933). Feature importance analysis revealed that the cumulative working time, as a situational variable, had the most significant impact on personal heat strain. These findings highlight the importance of systematic management of personal heat strain at construction sites by comprehensively considering the cumulative working time as a situational variable as well as environmental and personal variables. This study provided a valuable contribution to the construction industry by offering a reliable and accurate heat strain forecasting model, enhancing the health and safety of construction workers.

Effects of the strain rate on the tensile properties of a TRIP-aided duplex stainless steel

Choi, J.Y.,Lee, J.,Lee, K.,Koh, J.Y.,Cho, J.H.,Han, H.N.,Park, K.T. Elsevier Sequoia 2016 Materials science & engineering. properties, micro Vol.666 No.-

<P>Factors influencing the strain-rate dependence of the tensile properties of TRIP-aided lean duplex stainless steel were investigated by employing several characterization techniques of EBSD, TEM, and nanoindentation. The steel exhibited excellent tensile strength over 800 MPa and elongation, which exceeded 70% at a strain rate of 10(-3) s(-1) due to strain-induced martensitic transformation (SIMT), but both values decreased considerably with an increase in the strain rate. The hardness and the maximum shear stress for dislocation nucleation of the austenite were found to be higher than those of the ferrite by sub-grain scale nanoindentation tests. As a result, strain partitioning to the ferrite rather than the austenite was more significant from an early stage of deformation, suppressing the SIMT in the austenite. An EBSD strain analysis on the intra- and inter-grain scale revealed that this strain partitioning became more pronounced as the strain rate increased. Adiabatic heating, which induces austenite stabilization, also became more significant as the strain rate increased. Therefore, the present results indicate that the diminishing TRIP effects at high strain rates can be attributed to preferential strain partitioning to the soft ferrite phase from an early stage of deformation, as well as adiabatic heating. (C) 2016 Elsevier B.V. All rights reserved.</P>

Heat Strain Index using Physiological Parameters while Wearing Personal Protective Equipment: Biomonitoring Technology

( Joo Young Lee ) 한국감성과학회 2015 추계학술대회 Vol.2015 No.-

The purpose of this lecture was to present and discuss about heat strain index using physiological parameters while wearing personal protective equipment (PPE) in terms of biomonitoring technology. Firefighters’ PPE was used as an example. Minimum requirements for next generation of PPE to alleviate the heat strain of firefighters in the field were discussed. Two performance levels were given for the performance requirements: (1) activity and (2) rest breaks. Regarding the activity level, two kinds of activities were given for the requirements: (1) running exercise on a treadmill, (2) a simulated mobility test. The simulated mobility test can be modified from US, Canadian or Japanese mobility test protocol. While firefighting wearing full PPE in hot environments, foot temperature can provide an early warning sign to avoid heat-related illness of firefighters: 38.0℃ of foot temperature (Attention), 38.5℃ of foot temperature (Warning), and 39.0℃ of foot temperature (Danger). The combination of foot temperature and heart rate can play a role as a physiological strain index to avoid heat-related illness of firefighters: PSIfoot = 5(Tfoott .37.0) / (39.5 .37.0) + 5(HRt-HR0) / (180-HR0). While resting between firefighting in the field, heart rate can provide safety limit duration to avoid overheating firefighters prior to the consecutive work, when the upper limit of rectal temperature is set at 39.0℃: Tre(t) = 0.035 HRrelative + 35.83 + (8·HRrelative-66)·10-4·t.

Determination of line heating conditions for plate forming using the strain directed boundary method based on deformation superposition

윤희찬,노홍준,Young-Hwan Han,Hun Bong Lim,양현익 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.11

This study proposes a method to determine the location, magnitude, and sequence of line heating to form a target shape using the strain directed as boundary (SDB) method. The analysis model was constructed by considering the phase transformation caused by line heating. The results of the analytical model were compared with the experimental results. The deformation at an arbitrary heating location and heating magnitude was calculated using a verified model. The locations and magnitudes were determined by optimization. The deformation reflecting the optimization result confirmed an error of 5.91 % compared to the experimental results. The scale factor for the optimal heating sequence was determined via optimization by line heating sequence. The deformations caused by the heating sequence of the concave and saddle shapes confirmed errors of 7.04 % and 8.59 %, respectively. The proposed method provides guidelines for heat forming.

콤솔 멀티피직스를 이용한 2차원 탄소성 인장 암석권 모형에서 발생하는 전단열에 관한 수치 모사 연구

조태환,소병달 한국지구물리.물리탐사학회 2020 지구물리와 물리탐사 Vol.23 No.1

In the development of geodynamic structures such as subduction and rift zones, a weakening mechanism is essential for localized weak zone formation in the lithosphere. Shear heating, a weakening mechanism, generates shortwavelength temperature elevation in the lithosphere; the increased temperature can reduce lithospheric strength and promote its breakup. A two-dimensional elastoplastic extensional basin model was used to conduct benchmarking based on previous numerical simulation studies to quantitatively analyze shear heating. The amount of shear heating was investigated by controlling the yield strength, extensional velocity, and strain- and temperature-dependent weakening. In the absence of the weakening mechanism, the higher yield strength and extensional velocity led to more vigorous shear heating. The reference model with a 100-MPa yield strength and 2-cm/year extension showed a temperature increase of ~ 50 K when the bulk extension was 20 km (i.e., 0.025 strain). However, in the yield-strength weakening mechanism, depending on the plastic strain and temperature, more efficient weakening induced stronger shear heating, which indicates positive feedback between the weakening mechanism and the shear heating. The rate of shear heating rapidly increased at the initial stage of deformation, and the rate decreased by 80% as the lithosphere weakened. This suggests that shear heating with the weakening mechanism can significantly influence the strength of relatively undamaged lithosphere. 섭입 및 열개와 같이 대변형을 수반하는 지구동역학적 현상 발생은 암석권의 국지적인 약대의 발달이 필요하다. 이러한 약화 기작 중 하나인 전단열은 암석권의 온도를 국부적으로 높여 강도를 낮추는 역할을 하여 암석권 파괴를 촉진시킬 수 있다. 본 연구에서는 전단열에 대한 정량적인 분석을 위하여 2차원 탄소성 인장 분지 모형을 제작하여 기존수치 모사 연구를 벤치마크하였다. 암석권의 항복강도, 인장 속도, 변형량- 및 온도-의존성 약화 현상 등을 조절하여 전단열 발생량에 미치는 영향을 분석하였다. 실험 결과, 약화를 고려하지 않은 경우 전단열의 발생량은 암석권의 항복강도및 인장 속도와 양의 상관관계가 있는 것으로 나타났다. 기준 모형인 항복강도 100 MPa, 인장 속도 2 cm/yr로 설정된 경우, 총 20 km 인장된 시점(0.025의 변형률)에서 ~ 50 K의 온도 상승을 보여주었다. 소성 변형 및 온도에 따른 약화가 포함된 경우에는, 더 효율적인 약화 기작이 더 강한 전단열의 생성으로 이어지는데 이러한 현상은 약화 기작과 전단열 발생 사이에 양성되먹임이 작용함을 지시한다. 또한 변형 초기에 급격한 전단열 발생량을 보여주지만, 변형이 지속되어 암석권의 강도가 약화되면 전단열 발생 속도가 최대 ~ 80% 감소했다. 이는 약화 기작이 포함된 경우 전단열은 비교적 손상되지 않은 상태인 암석권의 강도에 큰 영향을 미침을 시사한다.

Prediction of Welding Deformation of Hull Panel Blocks Using an Advanced Inherent Strain Analysis Method Considering the Heat Equivalent Layer Effect

Hyung-Suk Mun,Chang-Doo Jang 대한금속·재료학회 2011 METALS AND MATERIALS International Vol.17 No.6

When a large-scale structure is fabricated via a complex welding process, deformation and residual stress are challenges that must be resolved. In a thermo-elasto-plastic analysis, calculations are carried out from room temperature through the heating and cooling of the welded joint section where the base metal is melted by the welding heat. It is difficult to apply this type of analysis to large, complex structures due to the prolonged computational time and huge processing volume required. Inherent strain analysis is a more effective approach to analyzing welding strain, and enables the use of an elastic analysis instead of a thermo-elasto-plastic analysis to predict the strain residual stress that occurs in the welded part. This study compares an existing method that analyzes the strain in the welded part by using the correlation between the zone affected by the heat and the adjacent zone constraining the heat-affected zone, and an advanced analysis method that is intended to enhance the accuracy of the results by considering the heat equilibrium zone that exists between the adjacent regions constraining the heat-affected zone. The advanced inherent strain analysis method is applied to obtain more accurate results for a hull panel block model, which is one of the most complex welding structures, by considering a restraint diagram organized according to the welding and fabrication sequence of the members.

Comparison of the Impact of an Optimized Ice Cooling Vest and a Paraffin Cooling Vest on Physiological and Perceptual Strain

Mansoor zare,Habibollah dehghan,Saeid yazdanirad,Amir hossein khoshakhlagh 한국산업안전보건공단 산업안전보건연구원 2019 Safety and health at work Vol.10 No.2

Background: Ice cooling vests can cause tissue damage and have no flexibility. Therefore, these two undesirable properties of ice cooling vest were optimized, and the present study was aimed to compare the impact of the optimized ice cooling vest and a commercial paraffin cooling vest on physiological and perceptual strain under controlled conditions. Methods: For optimizing, hydrogel was used to increase the flexibility and a layer of the ethylene vinyl acetate foam was placed into the inside layer of packs to prevent tissue damage. Then, 15 men with an optimized ice cooling vest, with a commercial paraffin cooling vest, and without a cooling vest performed tests including exercise on a treadmill (speed of 2.8 km/hr and slope of %0) under hot (40 C) and dry (40 %) condition for 60 min. The physiological strain index and skin temperature were measured every 5 and 15 minutes, respectively. The heat strain score index and perceptual strain index were also assessed every 15 minutes. Results: The mean values of the physiological and perceptual indices differed significantly between exercise with and without cooling vests (P < 0.05). However, the difference of the mean values of the indices except the value of the skin temperature during the exercises with the commercial paraffin cooling vest and the optimized ice cooling vest was not significant (P > 0.05). Conclusions: The optimized ice cooling vest was as effective as the commercial paraffin cooling vest to control the thermal strain. However, ice has a greater latent heat and less production cost.

Comparison of the Impact of an Optimized Ice Cooling Vest and a Paraffin Cooling Vest on Physiological and Perceptual Strain

zare, Mansoor,dehghan, Habibollah,yazdanirad, Saeid,khoshakhlagh, Amir hossein Occupational Safety and Health Research Institute 2019 Safety and health at work Vol.10 No.2

Background: Ice cooling vests can cause tissue damage and have no flexibility. Therefore, these two undesirable properties of ice cooling vest were optimized, and the present study was aimed to compare the impact of the optimized ice cooling vest and a commercial paraffin cooling vest on physiological and perceptual strain under controlled conditions. Methods: For optimizing, hydrogel was used to increase the flexibility and a layer of the ethylene vinyl acetate foam was placed into the inside layer of packs to prevent tissue damage. Then, 15 men with an optimized ice cooling vest, with a commercial paraffin cooling vest, and without a cooling vest performed tests including exercise on a treadmill (speed of 2.8 km/hr and slope of %0) under hot ($40^{\circ}C$) and dry (40 %) condition for 60 min. The physiological strain index and skin temperature were measured every 5 and 15 minutes, respectively. The heat strain score index and perceptual strain index were also assessed every 15 minutes. Results: The mean values of the physiological and perceptual indices differed significantly between exercise with and without cooling vests (P < 0.05). However, the difference of the mean values of the indices except the value of the skin temperature during the exercises with the commercial paraffin cooling vest and the optimized ice cooling vest was not significant (P > 0.05). Conclusions: The optimized ice cooling vest was as effective as the commercial paraffin cooling vest to control the thermal strain. However, ice has a greater latent heat and less production cost.

A study on the simulation of water cooling process for the prediction of plate deformation due to line heating

Nomoto, Toshiharu,Jang, Chang-Doo,Ha, Yun-Sok,Lee, Hae-Woo,Ko, Dae-Eun Korean Society of Ocean Engineers 2011 International journal of ocean system engineering Vol.1 No.1

In a line heating process for hull forming, the phase of the steel transforms from austenite to martensite, bainite, ferrite, or pearlite depending on the actual speed of cooling following line heating. In order to simulate the water cooling process widely used in shipyards, a heat transfer analysis on the effects of impinging water jet, film boiling, and radiation was performed. From the above simulation it was possible to obtain the actual speed of cooling and volume percentage of each phase in the inherent strain region of a line heated steel plate. Based on the material properties calculated from the volume percentage of each phase, it should be possible to predict the plate deformations due to line heating with better precision. Compared to the line heating experimental results, the simulated water cooling process method was verified to improve the predictability of the plate deformation due to line heating.