As a door expert witness, I'm called upon many times a year to gauge garage door injuries. Garage doors can be found in many shapes and sizes. Their functions range from basic security of an area to cosmetic concealment. Most doors could be broken on to a couple of basic styles or categories. Typical modern garage doors for residential applications tend to be predominantly of the overhead sectional variety. That type of door comes in many configurations, materials, levels of insulation, and a wide selection of appearance possibilities. They are available as a prefabricated kit, or built as a custom design to check the decor of any building. Commercial warehouse type installations often dictate higher security requirements. The ideal choice for this security kind of door may be the "roll-up" style that resembles a spin top desk kind of door. This door could be manufactured with many different materials that is as strong as the adjacent walls, making forced entry through this opening very difficult. Other common commercial installations include light weight aluminum single or sectional panel doors. These doors function more for closing off a currently secured area than for assuring point security.
In the past, the biggest concern with operating an overhead garage door was the potential risks related to the springs employed for balancing the door weight. Pre mid 1960's garage door installations typically relied upon a pair of stretched (tensioned) springs to assist the operation of the garage door pivoting hinges. These springs became loaded (tensioned) as the door was moved in to the closed position. Unloading (releasing) of the stored spring energy occurred as the door was opened to the horizontal overhead position. One of the very dangerous facets of these spring systems was that after a time frame, often without the maintenance or inspection, the points of attachment of these springs would rust or become weak. This weakening of the springs or points of attachment would often result in an inadvertent explosive failure flinging the broken spring components throughout the garage, embedding the spring or steel components in to the garage walls, cars or other items in the path of travel. Unfortunately, sometimes everyone was in the path of travel of these explosive occurrences. As these springs failed, being an attempted safeguard, some manufacturers devised a "caging" system for the springs. These cages were retrofitted onto the stretched springs in an endeavor to recapture the parts that will release in case a failure occurred. While these caging devices were helpful, these were not completely effective. Several of those spring devices are still in use today. Whenever this disorder exists or the caliber of garage components is questionable, a qualified professional service technician must certanly be consulted.
In response to the inherently dangerous old-style garage spring issues as above, a more recent and safer system for opening the overhead garage door was created. The theory was to transfer the load or weight of the door via a cable and pulley system to a vertical rod now equipped with a torsion (twisted) spring. This sort of spring is installed with specialty hardware and bolts to a fixed plate at one end, while the whole spring is installed around an outside pipe. This load balancing device is usually installed directly on the header of the garage opening. Using appropriate cables, connectors and pulleys, the weight of the garage door is transferred in to the torsion spring system. The difference involving the old-style stretched spring and the newer torsion spring is the way that the spring energy is stored. With the old-style stretched spring, the vitality is stored and released by pulling on the spring or returning the spring to its un-stretched condition. With a torsion kind of spring, the vitality is imparted or removed by rotating the spring clockwise or counter clockwise depending upon the direction of usage. With professional installation, the whole loading of the torsion spring is controlled by the garage installer, and is decided by the weight and size of the garage door that it's operating. When this type of torsion spring fails, it remains attached and intact to the place on the horizontal control rod where it had been mounted. I haven't been aware of or seen any torsion spring fly across a storage, creating injury from failed components just like the stretched older style garage door springs. That is not saying that injuries haven't occurred with the torsion style spring. The installing of this type of spring is generally safe when left to a trained garage door installation professional. Severe and serious injuries have occurred when untrained, unqualified individuals have attempted to set up or service this type of spring.