Now that the four-day fire is out at a Houston-area chemical storage complex, the real danger has emerged.

Cancer-causing benzene is wafting across the eastern suburbs of the fourth-largest U.S. city, shutting roads, schools and industrial plants, and disrupting everyday life. A major oil refinery in the heart of North America's most important fuel-producing region told workers to stay home and the cities of Deer Park and Galena Park told everyone to shut their windows and stay inside. The Texas National Guard deployed about 20 troops to assist with air monitoring, Maj. Joshua Amstutz said in an email.

Toxic fumes detected hours before dawn have panicked Houstonians normally accustomed to orange flares from the warren of refinery and chemical plant smokestacks that stretch to the eastern horizon. Even when the chemical fire erupted Sunday and sent a black anvil of smoke a mile above the city, many residents were nonchalant.