Mayor's Office memo re: DEP meeting, Mar 2002

NYC 9/11 Public Portal Document Friday 15 of Mar 2002, Mayor Office ->718 595 4544 Page 19 of 29

APPENDIX B: PERFORMANCE STANDARDS

Requirements and Performance Standards Cleaning Masonry Exteriors

I. Requirements

General: All work related to historic buildings shall comply with the Secretary of the Interior's Standards for the Treatment of Historic Pr;;perties. Treatment approaches will be in the "gentlest means possible," and all methods should be material and building specific. Programs for the cleaning of historic building facades shall be developed on a case-by-case basis with regard to each building and all associated building materials. Harsh treatments and inappropriate cleaning methods, including abrasive cleaning and certain chemical applications, can damage significant historic building fabric and character-defining features. Traditional abrasive applications such as "sand-blasting" and high-pressure water cleaning shall not de used.

II. Performance Standards

Qualified Contractor(s)/Consultant(s): A qualified professional such as a historic preservation or building conservation expert shall be consulted to develop an appropriate cleaning program for each building and to direct the work. A qualified contractor experienced in the cleaning of historic buildings shall perform the work.

Testing: Prior to cleaning a building, the source and type of soiling, dust, dirt, or debris shall be professionally tested. Identification of the type of soiling material, the type of building material (e.g. stone, cast stone, brick, terra cotta) combined with professional interpretation of test results will aid in the determination of the most appropriate cleaning method for a building. After a cleaning program is selected, the method shall be tested and evaluated by a professional prior to widespread application.

WTC Site Specific Considerations:

o It should be noted that post disaster cleaning of particulate soil and dust generated by the event should not be confused with cleaning of more persistent long term soiling that would require more aggressive methods.

o It is possible, based upon composition of the particulates generated by the event, that the dust and/or debris on the facade may chemically react with applications and masonry substrate during the cleaning process, creating deposits that will cau. problems to the building over time and that will be difficult to remove from building fabric. Dust and debris deposited on buildings should be tested for composition. If it is determined that a chemical reaction is possible, steps shall be taken to properly remove debris (from the projecting ledges or elements, sills, fire escapes) and dust from the horizontal and vertical surfaces of the building prior to the application of water or liquid cleaning agents. This may include vacuuming and/or gently brushing away dust from all horizontal and vertical

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