Cable fail-safe redundancy: Based on the proper setting of the drums on the torsion shaft, the two lift cables divide the lifting force equally to keep the door level as it rises. This not only levels the door, but also provides a fail-safe mechanism. If one of the cables should fail, such as from breaking or losing its end attachment, the other cable will then carry the full weight of the door. This will pull the door up on one side with twice the normal force, while the other side falls from its now unsupported weight, tending to make the door bind in its tracks and jam. Although not foolproof, this is a safety feature of the design which keeps the door from falling catastrophically if a cable were to fail while the door was traveling. The jammed condition also prevents a lowered door from opening with the hazard of a single broken cable, further minimizing the chances of both cables failing. Since if one cable fails the other must sustain the full weight of the door, the cables and attachments are rated many times the normal working load of half the door weight. A proper safety inspection of the door should include a critical look at the cables and their attachments.
Carter door: Garage doors in Florida come with extra bracing on the back and are wind-loaded to protect against hurricanes. The average with is 350 lbs. but some can weigh as much as 800 lbs. It can cost up to $1,000 dollars to replace a steel two-car garage door and if it's made of wood it can cost you up to $5,000 dollars. Some customized doors can be as much as 20 - 30k.
The material and style of your door as well as the replacement parts needed will impact the total cost of your project. It would cost less to install a steel door with no opener then it would to install a wood door with an opener etc... High tech doors come with enery-effecient glaze and thick insualation as well as finshed interiors and other upgrades. These doors are more expensive but are more reliable and durable.
First and foremost, a garage door, by design, contains springs designed to balance your door and make it easier to lift. Those springs are under incredible amounts of tension. If a spring breaks or is improperly released, it can cause incredible and potentially fatal injuries. Keep in mind, when working on a garage door spring, it is likely that your face and head will be close to it, meaning that your most sensitive area will be in the direct path of the released spring.