HERMISTON -- A monitoring crew at the Umatilla Chemical Depot detected trace amounts of mustard blister gas inside a depot igloo during routine monitoring Tuesday.

The igloo stores the chemical agent in ton containers.

A team of workers will enter the igloo to isolate the suspected container that has leaked and determine what to do, depot officials said Tuesday afternoon. A powered filtration system has been installed in the igloo as a precaution in addition to its passive filtration system that prevents mustard gas from escaping the igloo.

The amount of mustard gas detected was too small to be harmful to the public or the environment, depot officials said. The Umatilla Chemical Agent Disposal Facility plans to start incinerating the mustard gas this spring.