Measuring personal heat exposure in an urban and rural environment

Abstract

Previous studies have linked heat waves to adverse health outcomes using ambient temperature as a proxy for estimating exposure. The goal of the present study was to test a method for determining personal heat exposure. An occupationally exposed group (urban groundskeepers in Birmingham, AL, USA N=21), as well as urban and rural community members from Birmingham, AL (N=30) or west central AL (N=30) wore data logging temperature and light monitors clipped to the shoe for 7 days during the summer of 2012. We found that a temperature monitor clipped to the shoe provided a comfortable and feasible method for recording personal heat exposure. Ambient temperature (°C) recorded at the nearest weather station was significantly associated with personal heat exposure [β 0.37, 95%CI (0.35, 0.39)], particularly in groundskeepers who spent more of their total time outdoors [β 0.42, 95%CI (0.39, 0.46)]. Factors significantly associated with lower personal heat exposure include reported time indoors [β -2.02, 95%CI (-2.15, -1.89)], reported income>20K [β -1.05, 95%CI (-1.79, -0.30)], and measured % body fat [β -0.07, 95%CI (-0.12, -0.02)]. There were significant associations between income and % body fat with lower indoor and nighttime exposures, but not with outdoor heat exposure, suggesting modifications of the home thermal environment play an important role in determining overall heat exposure. Further delineation of the effect of personal characteristics on heat exposure may help to develop targeted strategies for preventing heat-related illness.

Keywords: Heat exposure; Occupational heat exposure; Outdoor versus indoor exposure; Personal exposure; Sunlight exposure.

Figure 1

Average (A, B) and maximum (C, D) daily personal heat exposure measurements (lines) compared to temperatures recorded at the closest weather station (circles). Average daily temperature exposure in 30 urban community members (A). and 21 groundskeepers (B). Maximum daily temperature exposure in 30 rural community members (C) and 30 urban community members (D). Each participant wore the monitor for 7 days and the study was conducted over a 3 week period during the Summer of 2012 (X axis).

Figure 2

Mean hourly outdoor and indoor heat exposure in urban groundskeeper, urban community and rural community participants. The median (25^th, 75^th percentiles) of the hourly mean temperatures recorded per participant on the data logging monitor when the daily log was marked outdoor or indoor (Groundskeepers =19, Urban =28, Rural =30). Notches represent 95% confidence intervals on median.

Figure 3

Outdoor, indoor, and nighttime heat exposure in obese (n=63) and non-obese (n=14) participants. The median (25^th, 75^th percentiles) of the hourly mean temperatures recorded per participant on the data logging monitor when the daily log was marked outdoor or indoor or during nighttime (12 AM to 5 AM) (Groundskeepers =19, Urban =28, Rural =30). Notches represent 95% confidence intervals on median.

Figure 4

Average daily light exposure in urban (Birmingham, AL-Bham) and rural (Southwest AL) community members and Birmingham (Bham) groundskeepers over the 3 week study period. Shaded areas indicate weekends