The first use of the term “pyrotechnics” for explosive and propellant-actuated devices in the aerospace field was by Harry Lutz of McDonnell Aircraft Company during the Mercury program.
In response to a concern voiced by program management about using explosive devices in close proximity to the astronaut, Harry said, “Don’t call them explosives, call them pyrotechnics.”
This was quickly shortened to “pyros,” which sounded evenless threatening.