The proposed 50 kTon magnetised Iron Calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) aims to detect atmospheric neutrinos and study the effect of Earth matter on their propagation and determine neutrino mass hierarchy. In addition to performing standard oscillation studies, ICAL can probe exotic phenomena like neutrino decay. A study of the sensitivity of the 50 kTon to the invisible decay
of the mass eigenstate ν₃ is studied. A full three-generation analysis including earth matter
effects is performed in a framework with both invisible decay and oscillations. The wide energy range and baselines offered by atmospheric neutrinos are shown to be excellent for constraining the ν₃ lifetime. It is found that with an exposure of 500 kton-yr, ICAL will be able to constrain the ν₃ lifetime to τ₃/m₃>1.51x10¹⁰ s/eV at the 90\% C.L by analysing charged current ν_μ + anti-ν_μ events. This is two orders of magnitude tighter than the bound from MINOS. The effect of invisible decay on the precision measurement of θ₂₃ and Δm₃₂ is also studied.