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... orate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302 Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. balance was developed to predict the extent to which ambient particles penetrate through vent holes and enter the interiors after the purge is off. This work describes the mathematical modeling analysis, supplementing with results from laboratory measurements using a cylindrical chamber as a simulated space telescope. It was found that the characteristic time for airborne particles to reach a saturation level, after the purge is off, can be characterized by the air-exchange rate and particle deposition rate inside the confined space volume. The air-exchange rate, measured using a tracer gas technique, is associated with the natural convection and air flow turbulence intensity adjacent to the chamber. During the purge outage, the steady-state airborne particle concentration inside the space telescope is governed by the ambient particle concentration, air-exchange rate, and particle deposition rate. SUBJECT TERMS Particulate infiltration, Intrusion, Purge outage 16. SECURITY CLASSIFICATION OF: a. REPORT UNCLASSIFIED b. ABSTRACT UNCLASSIFIED c. THIS PAGE UNCLASSIFIED 17. LIMITATION OF ABSTRACT 18. NUMBER OF PAGES 19 19a. NAME OF RESPONSIBLE PERSON De-Ling Liu 19b. TELEPHONE NUMBER (include area code) (310)336-0062 Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. 239.18