The plasma fire effect was created by filming a clear glass tray with hot water and granules of dry ice. This was then lit from the back and tinted green.
For the scene in which La Forge and Crusher evacuate the air from the cargo bay, miniature barrels were constructed and attached with pins to a vertical miniature floor. The pins were then removed, with the barrels falling against a blue screen. By shooting at a high frame rate, the desired effect was achieved.
The last episode aired before Gene Roddenberry's death on 24th October 1991. Unification I (1991) and Unification II (1991) began with the simple credit: Gene Roddenberry (1921-1991).
The song that Geordi sings is the opening lines of the Major General's Song from the W.S. Gilbert and Arthur Sullivan opera 'The Pirates of Penzance': "I am the very model of a modern Major-General, I've information vegetable, animal, and mineral." Another Gilbert and Sullivan tune, "A British Tar," is featured in Star Trek: Insurrection (1998) as Picard and Worf attempt to distract a malfunctioning Data.
Ronald D. Moore noted that the episode was The Next Generation's homage to The Poseidon Adventure (1972). To this end, Moore half-jokingly proposed casting Shelley Winters in the episode, but the idea was rejected.