at 3-40 kilovolts depending on size, making them the main concern among household appliances. historically, concern has focused less on the cathode ray tube, since its thick glass envelope is impregnated with several pounds of lead for shielding, than on high voltage (hv) rectifier and voltage regulator tubes inside earlier tvs. in the late 1960s it was found that a failure in the hv supply circuit of some general electric tvs could leave excessive voltages on the regulator tube, causing it to emit x-rays. the models were recalled and the ensuing scandal caused the us agency responsible for regulating this hazard, the center for devices and radiological health of the food and drug administration (fda), to require that all tvs include circuits to prevent excessive voltages in the event of failure. the hazard associated with excessive voltages was eliminated with the advent of all-solid-state tvs, which have no tubes other than the crt. since 1969, the fda has limited tv x-ray emission to 0.5 mr (milliroentgen) per hour. with the switch from crts to other screen technologies starting in the 1990s, there are no vacuum tubes capable of emitting x-rays at all.