We will be having a power outage in our building soon and our fridges are pretty full. The power will be off for about 10 hours. Will our food last safely during this time?
[Edited] I think 10 hours would be safe enough for most food: the first couple of hours the fridge will still be quite cold, and after that it takes more than a few ours for most food to spoil. When I leave milk out of the fridge for three hours at room temperature (say, 20 °C), nothing happens. I do this often. And the temperature inside the fridge will never reach room temperature in those 10 hours. When it is really hot in summer, it might spoil after 2 hours outside the fridge, but otherwise it takes much longer.
Cheese, food in jars, sauces, leftover cooked food: none of these are more sensitive to spoiling than milk. Fresh herbs are probably equally sensitive. Eggs are much less sensitive. The most sensitive kinds of food I can think of are probably raw meat and raw fish without preservatives. Smoked or salted meat and fish do not count: they can be kept much longer. I think even raw meat and fish will pull through, but you might want to apply the following tips to be sure.
Tip 1: put as much material in your fridge as possible, a day before the outage. That will "absorb the cold" that your fridge feeds it while power is still on. Then, once power goes out, the "cold reserve" in your fridge will be significantly increased, so that the average temperature of the interior will stay colder for a much longer time. The higher the volumetric heat capacity, the better. See this table ('volumetric heat capacity') for the best material; water probably wins. So stuffing bags of water in every nook and cranny would seem like a good idea. Or else bottles.
Tip 2: if you have a freezer, stuff it with bags and/or bottles of water, and put most of those in the fridge once power goes out (swap with some of the bags/bottles that were in the fridge). The freezer will probably do better, because it has much better insulation than the fridge. And put the most sensitive foods in the freezer maybe a few hours after power goes out (or maybe later—lest they freeze after all).
Actually, start putting as much water bags/bottles in the freezer as you can several hours before power goes out, and move them to the fridge once frozen. They will remain half-frozen for hours and hours in the fridge, so they will add extra coolness to the fridge. This way you're "saving up" cold from the freezer and increasing your cold reserve even more.
Tip 3: most refrigerators have a temperature slide/wheel/thing, which determines what temperature the thermostat aims at. You could set the slide to maximum power (so lowest temperature) a few hours before the power outage. Most people, including me, have the slide somewhere in the middle normally. The slide usually doesn't mark the exact temperature, but rather some symbols. It is usually found inside the refrigerator.
Tip 4: cook and/or eat any raw fish and meat before the outage. I think it would not be necessary at all if you follow the above tips, but cooking your meat now may just be simpler. Then either store the cooked meat or eat it. Incidentally, I wouldn't half-cook any meat: that may actually increase the rate of bacterial growth if it doesn't kill the bacteria completely. But something like salmon can be (fully) cooked first, reheated later.
As others have mentioned, it depends a lot on the efficiency of your fridge, how much or little food there's in, the temperature of the room the fridge is in and so on. The USDA has a whole page about “Keeping Food Safe During an Emergency.” A power outage of 10 hours seems rather long though considering they state you can expect the fridge to keep the food safe for about 4 hours (without any further preparations). Check the page for additional advice.
Keep the refrigerator and freezer doors closed as much as possible to maintain the cold temperature. The refrigerator will keep food safely cold for about 4 hours if it is unopened. A full freezer will hold the temperature for approximately 48 hours (24 hours if it is half full) if the door remains closed. Obtain dry or block ice to keep your refrigerator as cold as possible if the power is going to be out for a prolonged period of time. Fifty pounds of dry ice should hold an 18-cubic foot full freezer for 2 days. Plan ahead and know where dry ice and block ice can be purchased.
Ziplock bags of water in the freezer work great as ice-packs- for both the fridge and freezer.
Also, once my apartment was due to get hit by a hurricane when I would be gone for the weekend. I was concerned that the power might go out for an extended period of time and I'd have no idea how long the fridge was without power. Since I would be gone for several days, the fridge would easily have enough time to refreeze potentially spoiled food.
So to see if items in the fridge had melted and later refrozen, I left a frozen tray of ice cubes upside down in the freezer.
With this tip, if power is restored when you're away (or just during the night when you're asleep), then check to see if the ice cubes separated from the tray. If they're just loose, you're probably okay. But if they have melted at all then you know the freezer dropped below freezing long enough for items to melt. The size and shape of the melted ice cubes can also be a good indicator of how much melting occurred.