N.Y. Comp. Codes R. & Regs. tit. 12, § 21.6 – Working from window sills or ledges.

(1) A cleaner shall not be suffered or permitted to clean a window from the outside by this method except a window which is so constructed, equipped and maintained as to be safe for cleaning by the use of anchors and safety belts (herein called a safe window) and certain other windows below described.
(2) A safe window is one which complies with all of the following requirements:
1. (i) It shall not be horizontally pivoted.
2. (ii) If it is vertically pivoted or hinged it shall afford an unobstructed passage space to the exterior sill at least 16 inches wide and 40 inches high, and it shall be so constructed that when it is open it does not interfere with the attachment of the safety belt terminals to the anchors.
3. (iii) If it is double-hung or counterbalanced it shall afford an unobstructed passage space to the exterior sill not less than 21 inches wide and 30 inches high from the sill.
4. (iv) It shall afford a safe way of approach from an interior floor level to the passage space.
5. (v) It shall have an unobstructed sill or ledge providing a footing at least four inches wide for the full width of the window frame.
6. (vi) It shall have its movable parts readily operable and in good condition.
7. (vii) It shall be structurally adapted to an authorized installation of anchors.
  (b) Special windows.
(1) Where three windows with two separating mullions are set in the same wall opening, and the center window is a safe window and the sash openings of the two outer windows are less than 21 inches wide, this method may be used to clean the outer windows from a position on the sill or ledge of the safe window.
(2) Where three windows with two separating mullions are set in the same wall opening, and the two outer windows are safe windows, and the center window is not a safe window, this method may be used to clean the center window from a position on the sill of either safe window or astride either mullion.
(3) Where a single fixed sash window has adjacent thereto a safe window on either side with separating pilasters 16 inches or less in width and six inches or less in depth from their face to the glass and the fixed sash window has a sill at least three inches deep, this method may be used to clean the fixed sash window from a position on the sill of either safe window or astride either pilaster.
(c) Anchors required.
A window cleaned by this method shall be equipped with approved anchors, installed as authorized, and so maintained.
Exception:
A window having the sill or sills from which the cleaning is done not more than six feet above the ground, the floor or an equivalent surface.
(d) Safety belt required.
The cleaner shall be provided with an approved safety belt.
Exception:
When working from a sill or ledge not more than six feet above the ground or an equivalent surface.
(e) Attaching safety belt.
The cleaner shall attach one belt terminal to an anchor without extending more than one arm beyond the window sash before climbing out, and the other terminal to the opposite anchor before or immediately upon climbing out. When cleaning is done from an interior sill six feet or more high both terminals shall be attached to anchors before work is begun.
(f) Keeping both terminals attached.
The cleaner shall keep both belt terminals attached to separate anchors during the cleaning operation.
(g) Keeping one terminal attached.
The cleaner shall keep one belt terminal attached to an anchor until he has returned inside the window.
(h) Passing.
The cleaner shall not pass from one window to another or from one part of a multiple window to another at a level more than six feet above the adjoining floor or ground surface.
(i) Slippery sills.
The cleaner shall not work on a sill or ledge on which there is snow, ice or other slippery substance.
(j) Objects on sills.
The cleaner shall not stand or support himself on any object placed on a sill or ledge.
(k) Using defective anchor.
The cleaner shall not be suffered or permitted to use an anchor which is inaccessible, loose, damaged, deteriorated or altered.
(l) Using defective safety belt.
The cleaner shall not be suffered or permitted to use a safety belt which has been used for testing purposes or which is materially damaged, deteriorated or excessively worn in any part. A terminal slot is excessively worn if any point accommodates a nine-sixteenths inch plug gauge.

(a) Use of method.