Thermal deflector units use a variant of force field technology to generate a barrier against heat. The units may be tuned for varying efficiency levels of heat dissipation and deflection. As with most force fields, generator efficiency varies inversely with the area of the field generated.
The units may be networked and cross-connected to generate a broader or stronger heat shield. Such a configuration requires the units to be very precisely calibrated. Due to radiation and subspace interference often found in the environments where these devices are used, remote calibration is often not possible, thus experienced technicians may need to operate the units on-site.
Thermal deflector units were successfully employed to protect a colony on Bersallis III from firestorms while colonists were evacuated. The thermal barrier field was ultimately unable to deflect the path of the firestorms, however, and the colony structures were lost. Away team leader Lieutenant Commander Nella Daren was able to reconfigure the deflector units to protect the team members by generating tightly focused, very intense deflection pockets reinforced with their hand phasers. Unfortunately, one of the units was unable to withstand the force of the firestorms and two team members were lost. (TNG: "Lessons")