Machine-generated fog that&#039;s part of &quot;A Winter Landscape Cradling Bits of Sparkle&quot; by artist Jennifer Wen Ma, wafts over the installation in Pittsburgh&#039;s Market Square on Thursday, Feb. 26, 2015. The Pittsburgh Post-Gazette says firefighters have been called to the location at least twice, including once Thursday morning, by people who mistook machine-generated fog that&#039;s part of a new art installation for smoke. (AP Photo/Keith Srakocic)