you had to ask

Last evening, heard the phrase "blue air" in a technical conversation over the phone.

Wondered: What could that refer to -- "blue air"?

It must be a terminology specific to the area of expertise.
Cold air, maybe.
Special air that you pump from a can, mixed with some chemical. ...
Blue air.

So -- asked, after phone conversation finished:
"What is blue air?"

(The reply came with an energetic mix of aggravation and jubilance):
"BLEW air!
We BLEW air through it!
NOT 'blue air'!!!"

Hydraulics.
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Thank-you-and-good-night.

-30-