Editing Trench (section)

== Safety ==
Trenches that are deeper than about 1.5 [[meter|m]] present safety risks arising from their steep walls and confined space. These risks are similar those from pits or any steep-walled excavations. The risks include falling, injury from [[cave-in]] (wall collapse), inability to escape the trench, drowning and [[asphyxiation]].<ref name="OSHAtrenching">{{cite web |title=eTools:Trenching and Excavation |url=https://www.osha.gov/etools/construction/trenching |publisher=Occupational Safety and Health Administration (OSHA)}}</ref><ref name="NIOSHTrenching">{{cite web |title=Trenching and Excavation |url=https://www.cdc.gov/niosh/topics/trenching/ |publisher=The National Institute for Occupational Safety and Health (NIOSH)}}</ref>
* '''Falling''' into the trench. Mitigation methods include barriers such as railings or fencing.
* '''Injury from cave-in''', meaning collapse of a steep wall. Mitigation includes construction of sloped walls (''sloped trench'') or stepped walls (''benched trench''). For vertical walls, [[trench shoring]] stabilizes the walls, and [[trench shielding]] provides a barrier against collapsed material. The risk of cave-in increases from ''surcharge load'', which is any weight placed outside the trench near its edge. These loads include the ''spoil pile'' (soil excavated from the trench) or heavy equipment. These add extra stress to the walls of the trench.
* '''Inability to escape''' the trench because of steep and unstable walls, which may be difficult to climb. Ladders, stairs, or ramps allow exit. [[Crane (machine)|Cranes]] may assist rescue. 
* '''Drowning''' in water or mud that has accumulated in the trench from rain, seepage, or leaking water pipes.
* '''Asphyxiation, poisoning, fire and explosion''' from gasses that are denser than air that have settled in a trench. These may come from nearby industrial processing of these gasses, intentional use within the trench, or leakage from nearby plumbing. These present an [[asphyxiation]] hazard and may also be toxic. Burnable gasses such as [[natural gas]] present a fire and explosion risk. Oxidizers such as pure oxygen increase the risk of fire from other fuels present in the trench. Gasses such as pure [[nitrogen]] and [[natural gas]] have densities similar to pure air but are denser when cold, for example when they have evaporated from liquid form, and may creep along the ground and fill the trench. Ventilation fans and [[Duct (flow)|ducts]] reduce the risk. [[Oxygen]] sensors and other gas sensors detect the danger; alarms from the sensors can warn the occupants.