title: Evaluation of physiological strain in hot work areas using thermal imagery.
abstract: BACKGROUND
  Monitoring core body temperature to identify heat strain in workers engaged in hot work in heat stress environments is intrusive and expensive. Nonintrusive, inexpensive methods are needed to calculate individual Physiological Strain Index (PSI).
  
  
  OBJECTIVE
  Thermal imaging and heart rate monitoring were used in this study to calculate Physiological Strain Index (PSI) from thermal imaging temperatures of human subjects wearing thermal protective garments during recovery from hot work.
  
  
  METHODS
  Ten male subjects were evaluated for physiological strain while participating in hot work. Thermal images of the head and neck were captured with a high-resolution thermal imaging camera concomitant with measures of gastrointestinal and skin temperature. Lin's concordance correlation coefficient (rho_c), Pearson's coefficient (r) and bias correction factor (C-b) were calculated to compare thermal imaging based temperatures to gastrointestinal temperatures. Calculations of PSI based thermal imaging recorded temperatures were compared to gastrointestinal based PSI.
  
  
  RESULTS
  Participants reached a peak PSI of 5.2, indicating moderate heat strain. Sagittal measurements showed low correlation (rho_c=0.133), moderate precision (r=0.496) and low accuracy (C_b=0.269) with gastrointestinal temperature. Bland-Altman plots of imaging measurements showed increasing agreement as gastrointestinal temperature rose; however, the Limits of Agreement (LoA) fell outside the ±0.25C range of clinical significance. Bland-Altman plots of PSI calculated from imaging measurements showed increasing agreement as gastrointestinal temperature rose; however, the LoA fell outside the ±0.5 range of clinical significance.
  
  
  CONCLUSIONS
  Results of this study confirmed previous research showing thermal imagery is not highly correlated to body core temperature during recovery from moderate heat strain in mild ambient conditions. Measurements display a trend toward increasing correlation at higher body core temperatures. Accuracy was not sufficient at mild to moderate heat strain to allow calculation of individual physiological stress.
authors.affiliation: Rocky Mountain Center for Occupational and Environmental Health, Department of Family and Preventative Medicine, School of Medicine, University of Utah, Salt Lake City, UT, USA. Electronic address: clint.holm@utah.edu.
authors.forename: Clint A
authors.initials: CA
authors.lastname: Holm
authors.affiliation: Rocky Mountain Center for Occupational and Environmental Health, Department of Family and Preventative Medicine, School of Medicine, University of Utah, Salt Lake City, UT, USA.
authors.forename: Leon
authors.initials: L
authors.lastname: Pahler
authors.affiliation: Rocky Mountain Center for Occupational and Environmental Health, Department of Family and Preventative Medicine, School of Medicine, University of Utah, Salt Lake City, UT, USA.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Thiese
authors.affiliation: Rocky Mountain Center for Occupational and Environmental Health, Department of Family and Preventative Medicine, School of Medicine, University of Utah, Salt Lake City, UT, USA.
authors.forename: Rodney
authors.initials: R
authors.lastname: Handy
mesh_terms: D000328:Adult; D001831:Body Temperature; D001833:Body Temperature Regulation; D003430:Cross-Sectional Studies; D041981:Gastrointestinal Tract / Q000503:physiopathology; D006339:Heart Rate; D018882:Heat Stress Disorders / Q000000981:diagnostic imaging* / Q000503:physiopathology; D006358:Hot Temperature; D006801:Humans; D008297:Male; D008875:Middle Aged; D016273:Occupational Exposure / Q000032:analysis*; D011481:Protective Clothing; D012881:Skin Temperature; D013312:Stress, Physiological; D013686:Telemetry / Q000379:methods; D013817:Thermography / Q000379:methods
keywords: Core temperature; Heat strain; Heat stress; Hot work; Physiological strain index; Thermal imaging