0800054 - Hybla Fair - 1974 - 15:15 - Black&White and Color - HYBLA FAIR was an underground, horizontal line-of-sight (LOS) weapons-effects test conducted at the Nevada Test Site on October 28, 1974. The test had a relatively small design yield of less than 20 kilotons. This lower yield test was thought to be appropriate because an earlier, larger yield test caused loss of valuable data when the force of the detonation through the LOS pipe destroyed experiments. However, the HYBLA FAIR test had an insufficient yield to provide the amount of radiation necessary for the LOS experiments to perform as anticipated and the desired data was not obtained.

An LOS pipe allows scientists to take measurements of the effects of heat, blast and radiation. The pipe has a diameter ranging from a few inches to as much as 30 feet. Inside the pipe, with the nuclear device at the small end, experiments are set up to be exposed to the radiation effects, but not the shock and blast effects. These effects are prevented from rushing through the pipe by fast-closing steel doors. Radiation travels faster than blast and shock waves, thus allowing the doors to close and the radiation tests to be conducted.