Boiling point: in Tucson, not everyone is equal in the face of heat

As summers get more intense, people who work outdoors, those on a low income and the elderly face imminent peril

To live in Tucson is to be exposed. The Arizona city unfolds beneath four mountain ranges and a gaping sky, welcoming relentless sunlight. Anything here can be sun-bleached - billboards, garden hoses, family photos near windows, laundry left out to dry. Most of the year it's a dry heat, and sweat evaporates off skin faster than it's produced.

Summertime is different. In monsoon season, heat and humidity steadily increase until a storm breaks. There is no other release. Heat cannot exit from the body, creating a claustrophobic feeling inside the skin. Sweat becomes a vital sign - its absence indicates heatstroke.