When choosing a fortress purely for its safety, nothing on earth holds a candle to these artificial islands. Completely isolated from shore, with living and work spaces towering far above the waterline, even a bloated, floating zombie could never climb aboard. This makes security almost a non-issue, allowing you and your group to concentrate fully on the task of survival.
Offshore platforms also excel in self-containment, especially in the short term. As with ships, they carry their own living and medical facilities. Many are equipped to supply all their crew’s needs for up to six months. All have their own distilleries, so fresh water will never be a problem. Since all are equipped to mine either oil or natural gas, power will be unlimited.
Food is also plentiful, as the ocean provides a nutritious (and, some would argue, superior) diet of fish, kelp, and if possible, seaborne mammals. Unless the rig is extremely close to land, there is no danger of industrial pollution. People can, and do, live entirely, indefinitely from the riches of the sea.
This complete isolation, as attractive as it sounds, also presents its own brand of difficulties.
Anyone living near the beach will tell you what a killer salt air can be. Corrosion will be your number one enemy, eventually winning out against all preventative measures. Essential machines can be repaired. Cruder distilleries of steel pots and copper tubing work just as well as high-tech desalinizers. Wind- or tidal-powered dynamos could provide more than half the power of the fossil-fuel generators. Sensitive electronic gear, however, such as computers, radios, and medical machinery, will be the first to go and the hardest to replace. Eventually, the entire complex will deteriorate, from a cutting-edge industrial wonder to a crude and rusty albeit still serviceable hulk.
Unlike prisons and military bases, offshore oil rigs will be the first places abandoned. Within the first few days of an outbreak, workers will no doubt demand to get to their families, leaving the rig without a trained staff. If none of your group knows how to operate the machinery, learning might be difficult. Unlike prisons, there may not be a library with how-to books on every shelf. This may require a little creative improvisation, making do with what you can operate instead of, or until you can master, all the technology that can be found on most sophisticated rigs.
Industrial accidents-explosions of stored oil and gas-are bad enough on land. In the middle of the ocean, they have materialized into some of the worst disasters in history. Even with all the firefighting and rescue facilities of a living, functional world, entire crews have been killed when their rigs went up in flames. What would happen if a fire occurred and there was no one to cry to for help? This does not mean that oil rigs are sea-based bombs waiting to go off; it does not mean they should be avoided by all but the most foolhardy. What is recommended, however, is to shut down the drill. This may rob you of new petroleum but will work wonders for your life expectancy. Use already-stored fuel for the generator. As stated above, it will not give you the same amperage as the primary generator, but with the drill off and all industrial facilities closed, what will you need it for?
The ocean can be a source of life, but also a merciless killer. Storms, striking with a ferocity rarely seen on land, can smash even the sturdiest platforms. News tapes of North Sea rigs literally turning over, disintegrating to rubble, then sinking beneath the waves are enough to make anyone think twice about leaving shore. This is, unfortunately, a problem that cannot be remedied by humanity. Nothing in this or any other book can save you from nature when she decides to remove this hunk of steel from her ocean.