Green’s Dictionary of Slang

asbestos n.

an asbestos-coated theatre safety curtain.

[US]W. Winchell Your Broadway & Mine 16 Dec. [synd. col.] There were some cheers, too, when the last asbestos dropped on the [...] mellow drama.

In compounds

asbestos time (n.)

(US) the shutting of a theatre after the performance [the lowering of the safety curtain over the stage; note synon. UK theatre sl. the iron].

[US]W. Winchell Your Broadway & Mine 15 June [synd. col.] [She] appears in ‘Peggy Ann’ [...] at the Vanderbilt, and after asbestos time, works for La Guinan.