Disable the turbine. Kill AC power (turn off all the rectifiers and HVAC) and let the office run on battery for a while. Closely monitor the batteries, and the temperature in critical areas.
After a good while on battery (an hour or two, if I recall), walk leisurely over to the turbine and enable it. Let it start and warm up, then transfer the rectifiers and HVAC over to generator power.
Closely monitor the turbine while the batteries recharge, the HVAC while on unusual power, and the humans who are really glad to have air conditioning back.
When satisfied that all is copacetic, transfer things back to utility AC, shut down the turbine, and call the fuel company to top off the tank.
Most of the batteries in these offices were between 10 and 20 years old, with a couple instances of the beautiful cylindrical "Bell Cells" still in service. They were sized to not break a sweat running the whole building, and impeccably maintained, so they didn't tend to fail prematurely.
Once a quarter we'd do a live load transfer, and watch all the PDUs and UPS systems do their thing. Those could be stressful...