Backup generators operate during short intervals, not 24/7 for years. Even the pollution created during backup testing runs get documented and is a real point of concern for hospitals. The benefit however of having consistent power outweigh the drawback of temporary pollution.

I don't understand this knee-jerk pro-fossil fuel arguments, using your words. Fossil fuels, especially those in backup generators, are very harmful if run long term. We are currently in a pandemic where one of the primary causes of death is the inability to take up oxygen, and in this context we want to add air pollution?