Federal inspectors have found no signs of indoor air pollution at a Waterloo school. Earlier this month, a strange odor at Logan Middle School sickened about 30 people and forced the district to cancel classes for all or part of three days.

Investigators with the Environmental Protection Agency were asked to check the school after tests by local and state officials couldn’t find the source of the smell. Four federal inspectors were at the school two days last week, collecting air-quality samples.

The results of those tests have now been made public. E-P-A officials say the results show no evidence of anything that poses a threat to human health or the environment.

Audio: Elwin Huffman report. :30 MP3