Photo: Mason Trinca, Special To The Chronicle Photo: Santiago Mejia, The Chronicle

Cracked windows have been discovered at another San Francisco high-rise. And this time, it’s the big one — Salesforce Tower.

San Francisco’s Department of Building Inspection confirmed that the two windows — one facing south at the 12th floor and another facing east at the 14th floor — have cracked. The reasons are unknown.

The cracks are on the interior panes of double-paned windows, said Helen Han, a spokeswoman for Boston Properties, which owns Salesforce Tower, so “there was never any danger of glass falling to the street.”

Boston Properties discovered the cracks “within the last several weeks,” Han said in an email, and the panes should be replaced “in the next couple of weeks.”

DBI was made aware of them after an inquiry from The Chronicle.

In September, news that a cracked window had been found at a residence on the 36th floor of the sinking, tilting Millennium Tower — less than a block away from Salesforce Tower — kindled anxieties about whether the building’s structural problems were putting stress on that tower’s curtain wall — the layer of the building that includes its windows. Since it opened in 2009, the Millennium Tower has sunk by around 18 inches and tilted to one side, giving rise to a flurry of lawsuits over who is to blame.

Millennium’s window prompted officials to put up safety barriers around the building for weeks to prevent splintered glass from raining on the busy Mission Street sidewalk below. The crack was eventually determined to have been caused by some kind of external impact, but exactly what hit the window was never ascertained.

Neither DBI officials nor Boston Properties knows what caused the cracks at Salesforce Tower, but Han said the company had retained “top glass-safety consultants to help us determine the cause of these isolated failures and to take all necessary preventative steps. Working with our team of experts, we will also closely evaluate and monitor the condition of the glass throughout the building, with safety as our paramount concern.”

DBI spokesman Bill Strawn said Thursday that inspectors saw no indications that Salesforce Tower’s cracked windows were related to bigger structural problems.

Dominic Fracassa is a San Francisco Chronicle staff writer. Email: dfracassa@sfchronicle.com Twitter: @dominicfracassa