Applicable to cathode ray tubes and cathode ray tube assemblies which are intended for use as components in apparatus and which have integral protection with respect to the effects of implosion. A CRT covered by this standard is intended to be installed in an enclosure designed both to protect the rear of the CRT against mechanical or other damage under normal conditions of operation and to protect the user against particles expelled in a backwards direction from the CRT face in the event of implosion.