Trench Safety

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Excavations and Trenches are common on all construction sites.  Because of this, it is easy to lose sight of just how dangerous excavations and trenches can be.  But the thing is… they don’t have to be hazardous.  They do require planning, and execution of that plan, to ensure they are safe, but it is easy to keep everyone that works around or in an excavation or trench safe.

First, let’s clear up some definitions.  In construction the words excavation and trench tend to be used interchangeably.  However, from the perspective of safety, they are distinctly different words.  

Definition

  • Excavation – Any man-made cut, cavity, trench, or depression in an earth surface, formed by earth removal
  • Trench – A narrow excavation (in relation to its length) made below the surface of the ground.  In general, the depth is greater than the width, the the width of a trench (measured at the bottom) is not greater than 15 feet.  If forms or other structures are installed or constructed in an excavation so as to reduce the dimension measured from the forms or structure to the side of the excavation to 15 feet or less, the excavation is also considered to be a trench.

Real World Application

  • Take the shovel out of the back of your truck and dig a hole – Excavation
  • Take a backhoe and dig a hole 25′ x 25′ x 6″ deep – Excavation
  • Make that same hole 10′ deep – Excavation
  • Place forms in that Excavation to build a 20′ x 20′ basement – Excavation inside the forms & Trench outside the forms (between the forms and the dirt walls of the original excavation.
  • Take another backhoe and dig for some sort of utilities… total of 20′ long, 5′ wide, 8′ deep – Trench
  • Install those utilities and start back filling the trench to:
    • 6′ deep – Trench
    • 5′ deep – Trench
    • 4′ deep – Excavation

Explanation

By following the though process above it is easy to see why the words are used interchangeably, because one can easily transition to the other with just some minor changes.  But, regardless of what you call it, the ultimate goal and requirement is to make sure every employee that works in or around that excavation or trench is protected at all times and that they will go home safely at the end of the day!

There are several methods of protecting workers that are involved in this type of work, including but not limited to “Sloping”, “Benching”, “Trench Boxes”, “Trench Shoring”, etc.  

Hazardous Work

Construction inherently has “hazards” but that doesn’t mean it has to be “hazardous”.  Hazards can be anything that has the potential to cause harm: Medication, Hot Coffee, Gasoline…  These all have hazards.  Hazardous comes into play when you don’t take those hazards serious and you make risky decisions. 

To keep Excavations from becoming Hazardous it is important to:

  • Know the hazards associated with trenching and excavations. 
  • Understand the steps to address those hazards (sloping, benching, shielding, etc.)  
  • Take the necessary actions to abate those hazards (actually use what is available to address the hazards…sloping, benching, etc.)

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Excavation and Trenching

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One of the most dangerous types of construction work is excavation and trenching, which kills 40 construction workers every year. But these deaths can be prevented.

An excavation is defined as: any man-made cut, cavity, trench or depression in an earth surface, formed by earth removal.

A trench is defined as: a type of excavation or depression in the ground that is generally deeper than it is wide, and narrow compared to its length.

 Today we see OSHA inspectors assessing maximum fines to pressure employers into complying with the standard. Upon their inspection of a job site, these inspectors want to see that:

  • Employees are trained to safely perform their duties and they are involved in safety activities.
  • That a job safety program has been prepared and is effectively implemented.
  • That a Competent Person has been assigned to meet the requirements of the excavation standard.

 Every excavation must have a Competent Person.

The “Competent Person” is defined as one who is capable of identifying existing and predictable hazards in the surrounding or working conditions which are unsanitary, hazardous or dangerous to employees and who has the authorization to take prompt corrective measures to eliminate them.

Some of the responsibilities assigned to the competent person are:

  • Conduct tests for soil classification.
  • Understand standards and any data provided.
  • Determine the proper protective system.
  • Recognize and reclassify soil after changing conditions.
  • Determine if damage to trench safety equipment renders it inadequate for employee protection.
  • Conduct air tests for hazardous atmosphere.
  • Design of structural ramps.
  • Locate underground installations/utilities.
  • Monitor water removal equipment and the operation.
  • Perform daily inspections.

Always remember though, ALL employees must be trained to recognize and avoid hazards on site, as well as how to use protective systems properly.  Also, employees should never enter an excavation until the competent person has inspected and declared it safe for entry.

 Soil Types

OSHA’s classification system has 4 Types: Stable Rock, Type A, Type B, Type C.

  • Stable Rock: This is natural, solid mineral matter that can be excavated with vertical sides and remain intact.
  • Type A: This is a cohesive (clay  or clay  rich) soil with a compression strength of 1.5 tsf (tons per square foot) or greater. It is a hard soil that will bear a great load without failing.
  • Type B: This is a cohesive soil (medium to stiff clay) with an unconfined compressive strength between .5 and 1.5 tsf.
  • Type C: This is a cohesive soil (soft, wet clay) with an unconfined compressive strength below .5 tsf.

Most soils are either Type B or C. There is though, a C-60 Soil classification that was created by hydraulic shoring manufacturers, not OSHA. The competent person can only use this classification with a specific manufacturer’s tabulated data and equipment. (The worst flowing range of soil is C-80)

Protective Systems

The definition of protective systems means a method of protecting employees from cave-ins, from material that could fall or roll from an excavation face or into an excavation, or from the collapse of an adjacent structure. Protective systems include:

  • Hydraulic Shoring
  • Trench Boxes (Shielding)
  • Sloping
  • Benching
  • Sloping & Benching used in combination

According to the soil type, and depth of the excavation or trench, the competent person (or engineer, if depth of excavation is over 20 feet) will decide which of the above listed protective systems must be used.

Also, remember:

  • Always call 811 before you dig.
  • Ladders must be installed within 25′ of employees in trenches over 4′ deep.
  • Spoil piles must be a minimum of 2′ back from the edge of any excavation and …
  • NEVER enter an excavation or trench without the Competent Persons approval.

In closing, Ladies and Gentlemen, know that dirt is extremely heavy. One cubic yard of dry dirt is approximately 2000 pounds, or one ton – and this weight increases significantly when product is wet.

Be Safe! Be Aware!