It would be the 100/300 mA RCD.
The AFCI contains and RCD but also an electronic circuit that compares the waveform to known types of faults. It is therefore safer than an ordinary breaker, UL or IEC, if the electronic works. It might take them some time to fine tune the technology, but the manufacturers will sooner or later do it.
Owain is a bit harsh in his comments, but his reasoning is basically right. I wouldn't dare say there are big differences between UL and IEC breakers, but there are differences in the testing standards.
Another factor is what you blame fires on. It seems fires are started by arsonists in Sweden and electrons in America. (Exaggeration!)
[This message has been edited by C-H (edited 11-10-2005).]
