(CN) - Denver airport's use of de-icing fluid does not present a hazardous waste threat, the 10th Circuit ruled.
Airplane de-icing fluid, comprised mostly of propylene glycol, degrades into hydrogen sulfide gas, which has a rotten-egg smell and can have harmful health effects at concentrations starting around 5 parts per million.
Two United Airlines employees sued the city and county of Denver in 2005 after toxic levels of the gas were found in the basement of the airport's Concourse B, used almost exclusively by United.
After these incidents, the airport restricted full-plane de-icing at the gate, taking measures to better seal the building and tarmac, and performing full-plane de-icing on special pads farther away from the concourse.
But the airline employees proceeded with their lawsuit, arguing that without an injunction, full-plane de-icing at the gate would likely resume.
The district court denied their claims.
The 10th Circuit affirmed, saying the plaintiffs' claims under the Resource Conservation and Recovery Act were limited by the tentativeness of the word "may" in the statute's phrase "may present an imminent and substantial endangerment to health."
The gas would only be a problem if Denver's protective measures were proven ineffective, the Denver-based appellate court wrote.
"Nothing going on at the airport at the time of trial, or expected in the immediate future, would, even without remedial measures, present a prospect of harm to human health," Judge Harris Hartz wrote.
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