Space Station Freedom (SSF) modules may be unattended for months during the Man-Tended Capability (MTC) phase of the program. The accumulation of airborne contamination from materials offgassing or contingency incidents (e.g., thermodegradation) raise concerns about crew health and safety from the first crew entry throughout the MTC phase. Computer modelling of the MTC phase, and experiences from previous space flight missions confirm that caution must be exercised during nominal first entry operations.This paper will describe first entry procedures used in the industrial setting and examples of the consequences when first-entry procedures were not followed. Experiences during the Skylab program will be presented to highlight the necessity for carefully planned operations. Anecdotal experiences from previous Spacelab missions and the results of first entry samples from the International Microgravity Laboratory (IML-1) will be detailed. Operational scenarios will be outlined for nominal first entry procedures, which will be used to verify air quality before the crew enters the module.Three components of the Environmental Health System (EHS) will provide the necessary monitoring capability to protect crew health and safety during the planned first entry procedures of the MTC phase of the SSF program. This paper will describe each instrument and its role in first-entry operations.