A seat for a vehicle. The seat includes an occupant support defining a support surface for an occupant of the seat, and a mounting assembly coupled to the occupant support and rigidly mounted to the vehicle. The mounting assembly resists non-vertical movement and guides vertical movement of the occupant support relative to the mounting assembly. The seat also includes a shear member having a first hardness and a sacrificial member have a second hardness lower than the first hardness. The sacrificial member is sheared by the shear member in response to a generally downward force on the occupant support arising from inertia of the occupant in the presence of a rapid upward movement of the vehicle. Shearing the sacrificial member absorbs energy associated with the rapid upward movement of the vehicle and accommodates downward movement of the occupant support relative to the mounting assembly, reducing acceleration of the occupant.