BEHIND-THE-SCENES : LIQUID NITROGEN

Dan Curry began using liquid nitrogen extensively on Star Trek after watching Dick Brownfield, the series' special effects co-ordinator (which means physical/mechanical effects), using it on earlier Star Trek for warp core breaches and general mayhem. Dan Curry: I watched how it flowed around and realized it had other applications. I noticed that liquid nitrogen could look and behave much like fire. If you think of fire as a substance, it moves very quickly and disspates with sharp blades of flame. So if you have liquid nitrogen running down on a slanted black velvet surface, gravity will pull it one way; and then, if you blow it back with air guns the other way, it breaks up and looks like flame, especially if you overcrank the camera, shooting at 120 frames per second.

Dan Curry, [Star Trek Voyager]'s visual effects producer, as pictured on 30th July 2003 If you are thinking of using liquid nitrogen yourself, see Dan Curry's important warning and safety advice at the bottom of the page.

The operation requires several people to man the nitrogen air gets, and the fans. Curry gained valuable experience in the use of liquid nitrogen in [TNG: Lessons]. Dan Curry: We created huge banks of flame coming across the horizon using liquid nitrogen. His use of liquid nitrogen to create flame effects helped him win an Emmy Award for his visual effects in [TNG: A Matter Of Time], and an Emmy Award nomination for [#103 Thirty Days] in which he used liquid nitrogen to produce effects portraying the Moneans' contained water 'world' in space.

Dan Curry: We made a vat of liquid nitrogen about four inches deep. We were toying around with it and swatted it with some cardboard, and saw that the liquid nitrogen billowed out and then came back in an increasing tidal wave. By wrapping it around a digital sphere we were able to get the illusion that gases were being sucked into space. We actually used a vacuum cleaner and drew the nitrogen vapour out of the tank then, because it was heavier than air, it would fall back in. By placing a garbage-can lid on this vat and quickly pulling it up, the natural suction of the lifting lid created these wonderful tendrils of nitrogen vapour."

The VFX team on [Star Trek Voyager] received an Emmy nomination for their work on [#103 Thirty Days] but did not win the Emmy Award....because they won it for [#109 and #110 Dark Frontier]! Details of Emmy Awards nominations and wins for work on [Star Trek Voyager] are here.

Liquid nitrogen was used to create flame effects for the Kazon battle cruiser which is heavily damaged when Chakotay crashes his Maquis raider into it and which then crashes into part of the Caretaker's Array. For how the overall effect was done, including the liquid nitrogen part, see BEHIND-THE-SCENES: [CARETAKER] VISUAL EFFECTS: The Kazon Battle Cruiser.

From the crashing Kazon ship sequence:

[#1 and #2 Caretaker]

[#1 and #2 Caretaker]

See also Slideshow: 20 screenshots: Crash of the Kazon ship.

Liquid nitrogen elements are archived onto tape reels and have been employed on three Star Trek series ([TNG], [DS9] and [Star Trek Voyager]), and no doubt on [Enterprise] too. Dan Curry and other visual effects staff use them for nebulas, heat ripples, blowing dust, volcanic smoke, waterfalls, and flowing rivers.

The filmed nitrogen footage requires additional treatment. By its nature, liquid nitrogen is white and is usually filmed over black. During digital compositing, Dan Curry manipulates the white-on-black footage to achieve greater realism in his visual effects.

Dan Curry: With filmed liquid nitrogen footage, whether using it for fire or time-space anomalies, if you just tint it with the color of fire it always looks like you colorized a white element. I airbrush tonalities, whether it is in the orange or the red or the purples, and prevuild dissolves between these subtle forms that are airbrushed to suit the shapes of the phenomena we are trying to create. Keying [matte-ing] that prebuilt dissolve through the liquid nitrogen footage gives a much more natural luminescence than if you just make it a solid color.

When asked why he does not use CGI for organic effects: Dan Curry: Computer animation is wonderful and has given us a lot of freedom, but soe things it doesn't do all that well. Certain kinds of organic things are not completely convincing. There are compute procedurals that create wonderful moving textures and have nice kinetic properties, but computer fire, for example, still does not look real. So when we have something that calls for that kind of organic effect, we still like to rely on liquid nitrogen. Even the Badlands in the [Star Trek Voyager] pilot, which a lot of people think was pure CGI, really was not. We shot a lot of liquid nitrogen elements that we then gave to Amblin Imaging; they assembled them into layers and that became one of the building blocks of the Badlands sequence.

From the Badlands sequence:

[#1 and #2 Caretaker] the Maquis raider flees the Cardassian starship

[#1 and #2 Caretaker] the Cardassian ship is hit by a plasma storm

See also Slideshow: 14 screenshots from the Badlands sequence.

Behind-the-scenes: Flashback to [#44 Flashback] includes details of Sulu's reveal using liquid nitrogen

Dan Curry: Safety precautions are very important. It should be understood that liquid nitrogen is a dangerous material if mishandled. It is an extremely low-temperature substance, so if it drips on you it can burn your skin very severely. You should always wear very heavy gloves, and eye protection, because if it splashed in your eye you would be looking for a scholarship to the Braille school. Liquid nitrogen is not a toy. You really need somebody who knows how to handle it. I can't emphasize enough that it is something that should be used with great caution and with respect for its danger. Another thing, when people get into a cloud of nitrogen vapor it is cold and you can move around in it, but understand that you are inside a dense inert gas and there is no oxygen. It is safe to breathe it, recognizing that our atmosphere is made primarily of nitrogen, but it won't sustain your body. You could be asphyxiated.