The objective of this study was to quantify the degradation of neck muscle fatigue and its affect on subjective comfort associated with the prolonged wear of head-borne personal protective equipment (PPE) with modified mass properties for durations up to 4 h. A National Institute of Occupational Safety and Health approved chemical biological radiological nuclear modified air-purifying respirator (APR) and military ballistic helmet were worn. Neck fatigue was measured as a function of neck muscle activity, neck strength, and neck strength stamina/endurance. Comfort was measured through a subjective comfort/fatigue survey. During the 4 h wear trial, volunteers were required to complete typical first responder tasks, perform a visual search task, and walk on a treadmill. Seventeen volunteers completed the study. These volunteers tested eight different respirator and helmet equipment configurations of varied mass properties. The configuration head-borne weight ranged from 2.25 to 6.05 lb. Also, the configuration center of gravity and moments of inertia covered a broad range. PPE wear time was shown to be a significant variable with regard to neck fatigue and discomfort responses. Differences associated with APR and helmet mass property variations were not found to be significant. However, significant effects were seen when compared to the no APR/no helmet configuration.