MILWAUKIE, Ore. --
A chemical cloud in Milwaukie prompted crews to tell hundreds of people to stay inside Wednesday.
Firefighters say hydrofluoric nitric acid leaked from the titanium building at Precision Castparts on Johnson Creek Boulevard and the cloud drifted northwest, crews say.
The fumes formed when a power outage stopped the special filters that remove the hazardous chemical from the gas, a Precision Castparts spokesman says.
Clackamas Fire spokesman Steve McAdoo says the chemical can potentially irritate the respiratory system, but people shouldn't be in danger as long as they stay inside.
Four people -- two workers and two firefighters -- were taken to a hospital as a precaution and are OK.
The chemical is used in the casting process, authorities say.
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