Urban temperatures in Hong Kong: thermal environmental safety and implications for city planning.

Cutaneous thermal injury caused by direct contact with objects heated solely by sun exposure is rare. We undertook to investigate factors that may influence the temperature of sun-exposed objects at the ground level. Two clinical cases of burns caused by contact with sun-exposed objects are described. Surface temperatures on a citywide scale were determined from satellite thermal images. Ground level surface temperatures of a variety of objects were measured using an infrared thermometer. The satellite thermal image demonstrated local surface temperature differences (of more than 10.6 degrees C variation) and the temperature at the places of study (8.5-9.5 degrees C above background). Infrared thermometer readings demonstrated that the surface temperature of a sun-exposed black car could be as high as 75.0 degrees C (range, 71-78 degrees C) compared with 44.6 degrees C (42.2-47.3 degrees C) for a white car, and shading significantly reduced the surface temperatures of exposed objects (10.4-48.1%). The risk of injury is related to the effects of city planning on urban temperatures, of material color, composition, and shade on the ground level temperatures, and to the rise in global temperatures because of greenhouse-induced warming. The combined effect means that in a modern subtropical city such as Hong Kong, a substantial percentage of the urban area may have summertime surface temperatures that are high enough to constitute a health hazard. We recommend that this potential cause of harm to health be taken into account during urban planning.