An oil buffer is a hydraulic energy-dissipation device installed in the pit that decelerates the car or counterweight if it travels past the lowest landing. Oil is forced through metering orifices, absorbing kinetic energy rather than returning it, which is why oil buffers are classed as energy-dissipation type and are required for rated speeds above 1.0 m/s. Stroke length is calculated from rated speed, and EN 81-20 requires the buffer to return to its normal position and the lift to remain inoperative until it does.