In the 1890s, stages began to be equipped with drop curtains that had asbestos fibers woven into them and could be lowered as a fire barrier between the stage area and the auditorium. Unfortunately, most backstage fires could not be so easily contained. In Chicago's Iroquois Theatre fire of 1903, for example, the asbestos curtain snagged on some rigging and could not be lowered completely.
See also Theatre fires.
The Historical Dictionary of the American Theater. James Fisher.