The South Coast Air Quality Management District conducted tests on the material released during Wednesday's blast.
PHOTOS: Explosion at Exxon Mobil refinery in Torrance
The results, released this week, found no arsenic in the material and only traces of toxic hexavalent chromium.
Exxon Mobil officials earlier said the material might cause skin, throat and eye irritation but wasn't expected to be hazardous.
The tests also found no serious air pollution from the explosion, which left four people with minor injuries and heavily damaged equipment at the refinery.
The blast remains under investigation.