Is this an idiom?
"that would only add fuel to the flames" - catching fire

if it isn't then is it another literary device?

In at least 150 words, discuss the comparison described in the figurative language and how the connotative language reinforces the symbol. certainly the utmost rim of my first dome was filled with the tumultuous impression of soldiers marching to death for freedom's sake, of pioneers streaming westward to establish self-government in yet another sovereign state. only the great dome of st. peter's itself has ever clutched my heart as did that modest curve which had sequestered from infinitude in a place small enough for my child's mind, the courage and endurance which i could not comprehend so long as it was lost in "the void of unresponsible space" under the vaulting sky itself.