Depends on the fridge, type of food, etc. 4hrs is on the reg safe side, but I might not trust raw chicken by that time. Cured meats, hard cheese, veggies, most condiments, etc, should be good for much longer. We recently had an outage that started at 730pm planned for 7hrs (Ha!), started the genny at 7am before leaving for work for the fridge and freezers, and we lost nothing. Outage lasted until about 2pm. House was about 65F overnight, with no opening the fridge of course. The outage hurt the commercial guys cause of regs(similar to USDA), but most at home did alright if they had a full freezer and kept the fridge closed.