Fire-suppression foam accidentally spread over a wide area at the Oklahoma Army National Guard base in Tulsa on Tuesday morning, covering several helicopters, CBS News affiliate KOTV reported.
The foam caused no injuries and no damage to the helicopters.
The emergency foam was released during a test of the base's alarm and safety system by a civilian contractor. It filled the hangars and surrounded 10 Black Hawk helicopters.
Will Kavanagh, who flies Black Hawks at the base and is also a helicopter pilot for KOTV, said the contractor tests the safety system periodically. Only one of the base's 11 Black Hawks escaped being coated with foam, he said.
"It's hard to get to the shut-off valve when you have 15 feet of foam in the hangar," Kavanagh said. "Imagine being in the middle of the foam and trying to find your way around. It's like being in a fog bank without being to see in front of you."
He said because the copters are made for harsh conditions, the foam had no effect. Three of them were on the base's ramp outside the hangars and no foam got inside. The others were in the hangars undergoing maintenance and were exposed to the chemical, which is not harmful to the environment.
The contractor, SimplexGrinnell, cleaned up the foam at the ramp and the hangar, Kavanagh said.