Active Isolation for Seismic Protection of Operating Rooms

Keywords: Hospitals, Critical Facilities, Human Factors, Human Response, Isolation Devices, Vibration, Microtremors, TACMI, Weak Ground Motion, Active Isolation Devices, Control Algorithms, Floor Isolation, Computer Programs, and Computer Models.

Abstract: An evaluation of the protection of operating rooms from microtremors and frequent low-level earthquakes must take into consideration the threshold limits of the human response to vibration. In this paper, these threshold limits are adopted from a 1978 International Organization for Standardization (ISO) Standard on human response to vibration and are used as maximum limits for the evaluation of the performance of an active isolation device. The active isolation device, which is used to minimize the effects of the input vibration on the operating room, is an actual 6DOF combined passive and active floor isolation unit designed by the Takenaka Corporation and known as TACMI. An idealized SDOF computer model of the TACMI device was tested using the accelerogram of the NS component of the 1940 El Centro earthquake. The active control is based on an open-closed loop instantaneous optimal control algorithm which was found to be more effective than either an open loop or a closed loop algorithm. The responses of the uncontrolled and controlled systems are compared to the human vibration perception levels in the ISO Standard, showing that the active isolation model is able to reduce RMS acceleration to a level close to that of the human perception threshold. Based on these tests, it is proposed that active isolation devices like TACMI which, until now, have only been used to protect equipment or manufacturing processes, may also be installed in operating rooms or other areas where humans must perform delicate tasks.