D.C. Mun. Regs. tit. 24, r. 24-3201
In buildings having windows with sills ten feet (10 ft.) or more above the grade and constructed so that it is necessary for a person to clean the windows from the outside, approved safety devices for the protection of the window cleaner shall be provided and used.
In buildings where the window sill extends less than four and one-half inches (41/2 in.) from the window frame, an approved portable auxiliary sill or other approved device shall be provided and used, in addition to an approved safety belt.
Portable sills shall not be less than ten inches (10 in.) wide or less than thirty inches (30 in.) long.
Portable sills or other devices shall be designed and made so that they are safely held in place and can be readily put in position and removed.
The use of lag screws or expansion bolts as a means of fastening anchors is prohibited.
Window cleaners shall use safety devices provided for their protection.
Window cleaners shall not pass from window to window on the outside except where a railing is installed.
All anchor installations shall be maintained in a safe condition.
Where windows are constructed so that it is usual and practical to clean them from the inside, employers shall not allow any alterations, changes, or obstructions that will make it necessary to clean the windows from the outside, unless safety devices are provided.
D.C. Mun. Regs. tit. 24, r. 24-3201