Si Collection, Middle Volume
Radical: Fire (huǒ)
Page 668, Entry 13
Pronounced ba
According to the Discussion of Writing (Shuowen), it refers to the energy of fire.
Also, according to the Jade Chapters (Yupian) and the Collected Rhymes (Jiyun) and the Classified Chapters (Leipian), it is pronounced bie. According to the Jade Chapters, it means energy rising.