A force field is an energy barrier with many applications and varying degrees of strength. Although force fields had been in use for many years, Starfleet did not begin research on such a device until 2147, then referred to by Malcolm Reed as a "stable EM barrier." He made use of such a barrier to save several crewmembers, including Jonathan Archer. (ENT: "Vox Sola") By the 24th century, Federation Starfleet force fields were commonplace and were rated by intensity, ranging in strength from level 1-10. A level 10 force field is the strongest and would be used, for example, during a scientific experiment of which the outcome was unknown, or known to be explosive in nature. Applications range from creating holograms to sealing a hull breach to personal force fields designed to keep potential assailants at bay. (TNG: "Realm of Fear", "The Most Toys"; Star Trek Generations; Star Trek: Insurrection; DS9: "Playing God", "Starship Down"; VOY: "State of Flux", "Course: Oblivion")
During preproduction of Star Trek: The Next Generation, a type of device called a "landing envelope" would have placed "a protective power field envelope around a person or landing party, allowing away teams to visit planets with much more hostile environments than was possible in the past." The reference book Star Trek: The Next Generation 365 (p. 004) hypothesizes that the exclusion of this concept from the series may have been due to the strain it would have put on both the effects budget and, by lowering the amount of peril typically encountered on away missions, the writing staff. (Star Trek: The Next Generation 365, p. 004)
Sisko forcefieldJoran Dax in control of Benjamin Sisko bangs his head against a force field
The effects of a force field on its surroundings vary greatly. Contact with a force field may cause anything from a slight tingle to death. Most force fields are non-lethal, although some civilizations such as the Dominion prefer the lethal variety. If a force field is active, an object or transporter beam generally cannot pass through it, although this is not always the case. The Borg are known to not be hindered by most force fields; they can adapt and simply walk through the field. However, a Borg drone can be cut off from the Borg Collective if it is surrounded by a Starfleet level 10 force field. (DS9: "The Jem'Hadar"; TNG: "I Borg")
Force fields could be activated from various locations. On Starfleet starships there were emitter points at almost every junction along every corridor. The computer could be programmed to run a series of force field activations and deactivations within the ship, effectively creating a protected corridor which could follow a person. Commander Data used this technique with great control when he commandeered the USS Enterprise-D on stardate 44085.7. He also demonstrated another technique involving instructing the computer to implement a scan-series of force field activations, activated by his movements along a short distance of corridor, thus forcing the security team to back away from him. (TNG: "Brothers")
Soran's forcefield, Veridian IIITolian Soran's large force field active on Veridian III
If part of a humanoid body is caught in a force field while it is activated, the person may suffer second-degree burns on the affected area. (DS9: "Civil Defense")
Tolian Soran's force field on Veridian III generated an output of fifty gigawatts. (Star Trek Generations)
When various security measures left over from the Cardassian occupation came on-line on Deep Space 9, Elim Garak was recognized as a person of sufficient importance by the computer to have the force fields dividing the station drop when he approached. (DS9: "Civil Defense")
If necessary, a transporter platform can be completely enclosed within a force field, to, for example, contain an alien subject or prisoner during transport. (TNG: "The Hunted", "Realm of Fear"; VOY: "Death Wish", "Demon")
Force fields are also capable of selective positioning, allowing the majority of it to cover a secure location, while a smaller portion is deactivated to allow transport of food, drinks, and other items; particularly used when it would be considered dangerous to deactivate the entire force field. (VOY: "Repentance")