The world's oldest trenches are found where few people can see them: at the bottom of the sea. Seventeen of the Earth's major undersea trenches are found in the Pacific basin; one, the Marianas Trench, has been measured at more than 28,000 feet deep.
More recently, trenches were a major component in combat during World War I. Both the allies and the Germans dug trenches in which troops and supplies were held and moved around.
Even today, man-made trenches are a major component of construction and excavation sites. Injuries and deaths of entrenched workers can be caused by either natural disaster or human error.
According to PBS.org, each side had dug at least 12,000 miles of trenches by the end of World War I. The allied forces used four types of trenches: front line, support, reserve and communication.
Front-line trenches could be as close as 50 yards from a German trench. Supporting trenches contained troops and supplies for immediate movement to the front. Reserve trenches were several hundred yards farther back and held men and supplies for use when the front trenches were overrun. The communication trenches connected to many of the other trenches and facilitated movement of messages and supplies.
The Germans, by contrast, constructed bunkers with deep tunnels that frequently included underground living quarters with electricity, beds and toilets.
Digging trenches is one of the oldest forms of work and includes everything from cemetery application to construction and excavation. After World War I, developments in new equipment permitted the rapid digging of trenches and eliminated the need for back-breaking hand-digging.
But even today, before a trench is dug, soil must be tested to determine what is known as the "stand-up time," or how long the trench will function before its walls cave in. Soil type, weather conditions, and even the depth needed for the trench must all be considered before using the backhoe.
A trench box, or trench shield, is now often used to protect workers inside the trench. Made of steel plates, the shield is placed against the wall of the trench to prevent collapse.
Between 100 and 300 people are killed each year in trench collapses, and they remain among the most dangerous work sites in the construction industry. Though trench construction is monitored by the Occupational Safety and Health Association (OSHA), trench collapse is commonly caused by such factors as apparatus resting too closely to the trench, poor weather conditions, improper shoring or defective equipment.
Workers can fall into a trench or be struck by an object that falls in while they are working. Also, construction crew members can be electrocuted or burned if a pipe or wire ruptures during a dig. Entrenched workers are also at risk of suffocation from the release of gases, whether naturally occurring in such material as manure, or from a ruptured gas line.
Finally, trench collapse occurs when the ground materials of a trench collapse and bury a worker. The weight of soil can suffocate a worker or cause severe injuries such as broken bones and collapsed lungs.