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!

 

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