WikipediaのWARC Bandsには Due to their relatively small bandwidth of 100 kHz or less, there is a gentlemen's agreement that the WARC bands may not be used for general contesting. This agreement has been codified in official recommendations, such as the IARU Region 1 HF Manager's Handbook, which states: "Contest activity shall not take place on the 5, 10, 18, and 24 MHz bands."
とあり、摘示された後の方のIARUのリンクには Contest activity below 30 MHz should be restricted to the160 m, 80 m, 40 m, 20 m, 15 m and 10 m bands.