Wet synthetic air presents a challenge in the context of hydrogen leak detection due to overlapping of humidity loading, catalytic production and reabsorption of water in the near-field optical environment. An evaluation of the record of Pt nanodisk localized surface plasmon resonance (LSPR) with respect to a 215±10 nm diameter and 25 nm height nanoparticles, wideband resonance around 710 nm, synthetic air consisting of 20.5% O2 in N2 flowing at 200 mL min−1, temperatures of 33, 50, 80 and 100∘C, relative humidities of 0, 20, 50 and 80%, water feed rates of 0.081, 0.206 and 0.333 g h−1 at the humid levels, hydrogen concentrations of 0.06 to 1.26 vol%, 30–50 ppm low-concentration detection capability and a 143 h operation schedule with 114 h at 80% RH is presented. The issue of concern is whether a particular humid condition could enhance hydrogen readability without disrupting alarm reserve, recovery and order of appearance of the pulse. The concepts of signed spectral contrast, reservoir–thermal compatibility, sequence verification and alarm-recovery gating are applied to the present operational range. The 80∘C–80% RH level presents the strongest wet-air condition in terms of 𝒞RT = 1.000, alarm reserve of 0.950 for the 50 ppm detection limit and qualitative sequence agreement during the humid stretch.humidity does not have a positive effect in all cases; it is advantageous for Pt nanodisk LSPR in particular when near-field water, catalytic clearance, low detection limit, recovery and sequence persistence are correlated.