"The CE- Standard for Half- and Twin Ropes is different regarding the testing: twin ropes are always tested both pairs clipped into one biner (80kg mass, 12 falls), half ropes are... tested as a single rope with a 55kg mass (5 falls required). So the standard for half ropes is tougher than the one for twin ropes as half ropes also offer a great safety margin as a single rope (only to be used to belay two second climbers from an anchor). Therefore, half ropes can always be used in twin rope technique as well (whereas the other way round, twin ropes can not be used in half rope technique). The impact force is not affected by clipping one or two half ropes through the same biner."