1.   Air levels in the usually clear Bitterroot Valley have reached hazardous levels, prompting health officials to urge county school leaders to consider school closings if polluted air persists.

2.   Dozens of times every day, area firefighters speed to homes reporting hazardous levels of carbon monoxide.

3.   In addition, the laboratory found that some of the products when opened already had lead dust on their surfaces at potentially hazardous levels.

4.   The Coast Guard said the four proved that rear-mounted generator exhaust vents allowed carbon monoxide to collect at extremely hazardous levels around and under the swim decks.

5.   To prove the hazardous levels of arsenic in the surrounding area, Mark was overseeing testing for various lawyers and firms.

6.   A study by Harvard University researchers concludes that gasoline- and propane-powered ice surfacing machines may produce hazardous levels of nitrogen dioxide in rinks.

7.   An environmental group has sued to get warning labels slapped on chocolate products that caution sweet tooths about potentially hazardous levels of lead and cadmium.

8.   In recent months, schools and airports in several areas in eastern Malaysia, on Borneo island, were shut down as pollution levels soared to hazardous levels.

9.   In recent weeks, schools in Miri, Sipitang and other areas of Eastern Malaysia, on Borneo Island, were shut as pollution levels soared to hazardous levels.

10.   It was the second collision in the Strait of Malacca since hazardous levels of smog have blanketed Malaysia and other Southeast Asian nations in the last two months.