Safety Talks: Excavation Hazards and Risk Control

Excavation or trench is a manmade cavity required to perform various kind of jobs like building foundation, reservoirs, making roads in construction, oil and gas or in several other service industries however working in excavation is a hazardous job, workers working in excavation may face different risk factors an excavation is any man-made cut into the earth's surface formed by earth removal, a trench is a narrow excavation with a depth greater than its width but is no wider than 15 feet using protective systems and safe work practices can minimize trenching hazards for workers.

 

Picture: Excavation in progress at a Mining Site 

The biggest risk workers face during trenching and excavation work is the risk of death from soil caving in but other potential hazards do exist including workers falling into a trench hazardous atmospheres caused by toxic gases fumes or vapors entering the trench materials or objects falling into an excavation such as dirt removed from a trench or tools and materials damaged underground utilities that can expose workers to explosive or hazardous atmospheres or electrocution or even drowning and incidents involving mobile equipment such as being struck by an excavator to minimize these hazards pre-planning must take place prior to digging to ensure safe trenching and excavation operations before beginning any excavation a jobsite evaluation must be conducted by a competent person which includes evaluating soil conditions to determine their stability locating and marking existing underground utilities.   

 

Picture: a worker doing manual trenching on a site 

Before you dig service choosing the proper protective systems to prevent cave-ins providing a safe means of entering and exiting the trench or excavation testing for hazardous atmospheres inside the trench identifying overhead power lines and maintaining proper safe distances and planning for traffic control near the work area the competent person is responsible for the safety of workers in a trench or excavation and must inspect them daily to identify and eliminate any hazardous conditions before any worker can even enter this is because the conditions of the trench may change daily such as after a rainstorm weight of soil can vary but a good rule of thumb is that one cubic yard of soil can weigh approximately 3 000 pounds and dirt falling 6 feet can hit a worker with as much force as a pickup truck going 35 miles per hour therefore all workers who enter a trench or excavation more than five feet deep must be protected by sloping or benching of the earth or by shoring or shielding under the direction of the competent person.  

 

Let's take a look at each protective system sloping involves cutting back the trench wall at an angle inclined away from the excavation unless a trench is in solid rock the walls shouldn't be vertical without support if the dirt is granular and breaks up easily the trench wall needs to be sloped back farther than if the trench were in clay or more stable material for trenches up to 20 feet in depth you'll need a slope of one and a half feet back for every one foot down or 34 degrees in type c soil which is granular sandy and the least stable this includes most previously disturbed soils the maximum allowable slope is 1 to 1 or a 45 degree angle for soils that meet type b requirements and the maximum slope for type a soils such as clay is three quarters to 1 or an angle of 53 degrees benching is like sloping but the sides are vertical and then cut like steps just like sloping this method depends on the type and condition of the dirt you can sometimes use a combination of sloping and benching but benching cannot be done in type c soil a lot of jobs have very limited space and don't have room to slope or bench the sides of the soil back that's when protection like shielding or shoring should be used hydraulic shoring may be used on the job instead of sloping this pre-fabricated strut and whale system manufactured from aluminum or steel that supports the faces of the trench is designed to prevent cave-ins.

 

Picture: A Hyundai Excavator digging for deployment of underground telecom services 

All hydraulic shoring must be designed and set up in accordance with osha regulations manufacturer specifications or engineers designs if the trench is five feet or deeper hydraulic shores must be installed and removed without workers entering the trench a trench box or shield is another option to keep the walls from collapsing trench boxes are a frequently used protective system for utility line installations such as lateral lines they also provide protection to workers inside the trench when sloping cannot be used it's usually one piece so it's easier to install than other shoring systems once the trench is dug the box is placed in the hole and the sides of the box support the walls of the trench the box should be in good condition and be the right kind for the depth and soil type of the trench when they are used correctly the sides will be secure keep workers safe inside the protective system regardless of the type of trench or excavation following these additional work practices will help ensure the safety of workers provide a safe way to enter and exit a trench or excavation that is four feet or deeper such as with ladders steps or ramps.

 

If you use a ladder make sure it's no more than 25 feet away from you so you can get to it quickly when needed keep excavated dirt called spoils as well as materials and heavy equipment back a minimum of two feet from the edge of a trench to prevent anything from falling into it never enter a trench unless it has been inspected by a carpeted person or until there is a safe way to enter or exit other high visibility materials when working near moving equipment or vehicles and do not stand beneath loads handled by lifting or digging equipment keep heavy equipment away from trench edges and identify other sources that might affect trench stability locate and mark the exact location of underground utilities such as sewer water telephone or electric lines prior to digging keep a safe distance when working near overhead power lines and use a spotter for any hard to see separation distances or in tight areas install a barricade or fence around trenches or excavations that are left open to prevent unauthorized access remember incidents involving trench and excavation hazards can often be fatal so it's important to take all necessary precautions.